Alabama Lake Levels

Lake Name Current Level Full Pool +/- Full Pool Reading Date - Time
Andrews (AL) 76.76105-28.248/26/2015 7:00
Bankhead (AL) 254.5255.1-0.68/26/2015 8:03
Claiborne (AL) 34.55??? 8/26/2015 8:00
Demopolis (AL) 757328/26/2015 8:03
Eufaula (AL GA) 187.96188-0.048/26/2015 0:00
Goat Rock (AL GA) 401.28404-2.728/25/2015 9:49
Guntersville (AL) 594.9595.44-0.548/25/2015 11:30
Harding (AL GA) 519.9521-1.18/25/2015 9:49
Holt (AL) 186.3187-0.78/26/2015 8:03
Jordan (AL) 251.41252-0.598/26/2015 8:00
Lay (AL) 395.87396-0.138/26/2015 8:00
Logan Martin (AL) 464.8465-0.28/26/2015 8:00
Martin (AL) 488.43490-1.578/26/2015 7:00
Mitchell (AL) 311.94311.90.048/26/2015 8:00
Neely Henry (AL) 507.9508-0.18/26/2015 8:03
Pickwick (AL TN MS) 413.5414-0.58/25/2015 11:30
R.E. Bob Woodruff (AL) 125.41250.48/25/2015 8:14
Smith (AL) 505.24510-4.768/26/2015 4:00
Tallassee (AL) 287.2288.8-1.68/26/2015 8:03
Tuscaloosa (AL) 223.5229.96-6.468/26/2015 0:00
Wedowee (AL) 792.05793-0.958/26/2015 8:00
Weiss (AL GA) 563.84564-0.168/26/2015 8:00
West Point (AL GA) 633.93635-1.078/26/2015 9:15
Wheeler (AL) 555.8556.28-0.488/25/2015 11:30
William 'Bill' Dannelly (AL) 87.6807.68/25/2015 18:00
William Baker Oliver (AL) 124.6??? 8/26/2015 8:03
Wilson (AL) 507.5507.88-0.388/25/2015 11:30
Yates (AL) 343.03344-0.978/26/2015 8:00

There were some states this past summer of 2012 that were grossly affected by the worst drought conditions seen in years. One of these states was Alabama. The state of Alabama is releasing waters from the dams at intervals as lake levels were and continue to be at an all-time low. While there is a schedule for water released, this schedule can change at any time. The state of Alabama is asking people to enjoy the beauty of the lakes, but to use caution when on the water. Lakes that are situated in near proximity to the dams are dangerous, because when waters are released from the dams they become hazardous. Changes in water levels can also cause concern for people’s safety. Alabama’s rainy season is during the winter and spring, and weather changes can cause water changes very suddenly.

When the dams are opened more frequently during these times, it causes changes in the lakes that people need to be aware of and stay on alert if they are on the lake. They will need to do all they can to protect themselves and their property such as boats, water equipment and home properties. Because of the drought conditions the state of Alabama is trying to build up water levels in its reservoirs. If these droughts continue to increase Alabama will continue to try to conserve as much water as possible, and then release reservoirs into the lakes to help raise lake levels.

The state has provided citizens with an informational phone number for citizens to call and keep up on the changing Alabama lake levels. This important phone number to keep handy is as follows:
Alabama Power’s automated information system-800–Lakes11 (525-3711)
This number will give residents and tourists all the information that they will need on Alabama lakes, streams and river levels. It will also inform residents just when hydroelectric facilities will open spill gates. This will rapidly churn up the waters and make lake waters near dam sites very dangerous. Read schedules and know when spill gates will open. Better yet, do not take boats or swim near these spill gates, in order to practice safety first.

When Alabama weather changes and rain does come in access it can change Alabama lake levels quickly. Their lakes can rise quickly, so the state continues to caution it residents to practice safety at all times. Alabama has numerous lakes, streams, and rivers that tourists and residents flock to every year. People enjoy the water activities in Alabama, but one must read the news provided by the state about their water conditions, and how the rain can cause serious concerns on the water, and just how their hydro-generation plants work in regards to lake levels. Alabama is doing all they can in order provide tourists and residents a safe and fun Alabama holiday.

The water in Alabama is one of the state’s greatest natural commodities. The state emphasizes respect to their water systems, and wants everyone to understand that their waters provide transportation needs, food, recreations and energy needs to the state. The state of Alabama provides hydroelectric power to residents. The water in Alabama provides economic opportunity, plus recreation adventures. The waters supply irrigation to neighbors, and fresh clean drinking water for residents, tourists, water life, and wildlife. Alabama Power utilizes flood control to residents and tourists alike. Alabama says that it relies on their lake levels to sustain life of everyone in their state.

If you are a tourist or a resident wanting to participate in water activities, know the Alabama lake levels, and the levels of streams, and rivers before going out on the water. Know the schedule of the spill gates, and beware of lake areas adjacent to the dams. Don’t be caught off guard and get hurt, injured or become a casualty of death while enjoying your time on any of Alabama water systems.


Page 1  |  Page 2  |  Page 3

Layer Groups - viewed 98,465 times

Let me start by telling you that before Photoshop CS2 was introduced Layer Groups were called Layer Sets. The tutorial was written before Photoshop CS2 was released, so some of the screenshots are still based on Photoshop CS and you will read "Layer Set" in some of those.

Layer Groups are a great way to get your layers organized. The following image contains about 115 layers. Most of these layers however are hidden inside 11 Layer Groups . This has several advantages and some of which might not all be that obvious. For one thing it makes it easier to get things organized. Your layers palette will look less cluttered and there will be less need to scroll. But above all there are several interesting things you can do with layer groups. The more and more you use layer groups, the less you use linked layers.

You create a new Layer Group by clicking on the Layer Group icon Layers Palette at the bottom of your layers palette. It's important that you name your layer groups, otherwise you will get confused when you have a few of them.

Halloween image

In Photoshop CS2 you can select multiple layers (or a single one) and press Ctrl + G (Command + G on the Mac) to group them or you can drag and drop the layers on the Create a new group icon Layers Palette:

Move layers into Layer Group

A layer group allows you to turn off several layers all at once. The candle on the left is made out of 7 layers. To make the candle invisible, you just need to make the layer invisible (1 , bottom left, in front of the bowl).

Hiding or moving a Layer Set

It's easy to move layer groups. To move the candle on the right to a different spot, I just need to activate the layer that contains the candle and then I can use the move tool to move the candle to the background (2).
You might want to move the candle in front of the pumpkin, in that case your layer group with the candle will be higher in the layers palette than the the pumpkin layer group. It's the other way around if you want to move the candle behind the pumpkin.

It's easy to duplicate objects by dragging and dropping a layer group on the New Layer icon New Layer at the bottom of the layers palette. In this example I dragged the left candle layer and dropped it on the New Layer icon (3) and as a result a new layer was created with the name left candle copy. In this example I moved the layer group that contains the copy to the right using the Move Tool Move Tool, so that you can see that I now have two identical candles.

Duplicating a Layer Set

You can add a layer mask to mask parts of a layer group. In this example I've masked the stand of the candle (4).

Masking a Layer Set

You'll probably know that you can change the opacity of a layer. You can however also change the opacity of a layer group once activate it. This will change the opacity of the complete layer group.

Pass Through

A layer group has its own blending mode. By default the blending mode is Pass Through (6). This means that all the adjustment layers or layer blending modes inside the layer group will affect all layers below and outside the group.
In our example the green circle turned into olive. Once we change the blending mode to anything different than Pass Through, in our example Normal, then we see how the Hue & Saturation adjustment only effects the layers inside the layer group; the yellow square turned into olive, but the square kept its green color.

Layer Set's 'Pass Through' blending mode

You can also lock complete layer groups. Once you lock a layer group, all layers inside the layer group will be locked too (7).
This will also lock the layer group's opacity as you can see in this example.

Locking a Layer Set

Nested Layer Groups

Photoshop CS introduced nested layer groups, which means that you can have a layer group inside a layer group.
You can drag & drop a layer group on a another layer group or you can create a new one inside an existing group.

Menu options

You can click on the little triangle in the layers palette (5) to view a menu that has all kind layer groups related options that you can use.

Layer Set menu options

New Group From Linked
Layer Group properties
Merge Layer Group
: create a new layer group and moves all linked layers into this new group
: turn on/off specific channels or color your layer group inside the layers palette
: this merges all layers of any kind inside the layer group to a single layer.

Final words

Some people ignore the power of layer groups, thinking that it just about grouping layers and that's about it. You've learned by now that grouping layers is just part of the power of layer groups. It's what you can do with them what makes them really useful.
It's not always necessary to use layer groups, but once you're scrolling through 100 layers, you might consider to use them!

For more help with Photoshop check out ourPhotoshop Trainingsection.

Partner Sites
W3C XHTMLW3C CSSExplorerFirefoxOperaRSSRSS Valid


OUP user menu

ADAM15 regulates endothelial permeability and neutrophil migration via Src/ERK1/2 signalling

Chongxiu Sun, Mack H. Wu, Mingzhang Guo, Mark L. Day, Eugene S. Lee, Sarah Y. Yuan
DOI: http://dx.doi.org/10.1093/cvr/cvq060 348-355 First published online: 26 February 2010

Aims Endothelial barrier dysfunction is a key event in the pathogenesis of vascular diseases associated with inflammation. ADAM (a disintegrin and metalloprotease) 15 has been shown to contribute to the development of vascular inflammation. However, its role in regulating endothelial barrier function is unknown. The aim of this study was to examine the effect of ADAM15 on endothelial permeability and its underlying mechanisms.

Methods and results By measuring albumin transendothelial flux and transendothelial electric resistance in cultured human umbilical vein endothelial cell monolayers, we found that depletion of ADAM15 expression via siRNA decreased endothelial permeability and attenuated thrombin-induced barrier dysfunction. In contrast, endothelial cells overexpressing either wild-type or catalytically dead mutant ADAM15 displayed a higher basal permeability and augmented hyperpermeability in response to thrombin. In addition, ADAM15 knockdown inhibited whereas ADAM15 overexpression promoted neutrophil transendothelial migration. Further molecular assays revealed that ADAM15 did not cleave vascular endothelial-cadherin or cause its degradation. However, overexpression of ADAM15 promoted extracellular signal-regulated kinase (ERK)1/2 phosphorylation in both non-stimulated and thrombin-stimulated endothelial cells in a protease activity-independent manner. Pharmacological inhibition of Src kinase or ERK activation reversed ADAM15-induced hyperpermeability and neutrophil transmigration.

Conclusion The data provide evidence for a novel function of ADAM15 in regulating endothelial barrier properties. The mechanisms of ADAM15-induced hyperpermeability involve Src/ERK1/2 signalling independent of junction molecule shedding.

  • Endothelial permeability
  • Metalloproteinase
  • Vascular inflammation
  • Signal transduction

1. Introduction

Vascular endothelial (VE) cells constitute a semi-permeable barrier that controls the transport of fluid, solutes, and cells across the vessel wall. Endothelial hyperpermeability is considered one of the most important cellular processes in the development of inflammatory disorders, such as sepsis,1 atherosclerosis,2 and diabetic complications.3 The mechanisms underlying permeability regulation have been the subject of extensive investigation. It is commonly recognized that cell–cell adhesion and integrin-mediated cell–matrix interactions play a critical role in the maintenance of barrier function as well as in the mediation of responses to inflammatory stimuli such as thrombin.4

As an important type of cell–cell junctions in the peripheral vascular endothelium, the adherens junction is mainly composed of VE-cadherin and catenins. VE-cadherin mediates homophilic binding of adjacent cells via its extracellular domain and associates with catenins via its cytoplasmic tail, thereby linking the junction complex to the cytoskeleton.5 Disruption of the junction leads to increased vascular permeability; an effect seen in diseased vasculature with elaborated inflammatory mediators, including thrombin,6 cytokines, and VE growth factor.7 Moreover, the adherens junction participates in the regulation of leucocyte extravasation. For example, VE-cadherin disruption has been shown to facilitate monocyte transendothelial migration.8 Likewise, blocking VE-cadherin with antibodies promotes neutrophil migration.9 In addition to cadherin-mediated cell–cell interactions, integrin binding to the extracellular matrix strengthens endothelial barrier function. Competitive disruption of integrin-matrix interactions with RGD peptides causes endothelial hyperpermeability.10

ADAMs (a disintegrin and metalloprotease) are a family of type I transmembrane glycoproteins that have been implicated in inflammation, angiogenesis, and cancer growth and metastasis.11,12 Structurally, each ADAM molecule consists of a prodomain, a metalloproteinase domain, a disintegrin domain, a cystein-rich domain, an epidermal growth factor-like domain, a transmembrane domain, and a cytoplasmic tail.13 The metalloproteinase domain has a consensus HEXXGXXH sequence capable of degrading matrix14 and shedding cytokines,15 growth factor and growth factor receptors,16,17 and cadherins.18,19 The disintegrin domain of human ADAM15 contains an RGD sequence that can regulate integrin binding and subsequent cell–cell and cell–matrix adhesions. In addition to the proteolytic and adhesive properties, ADAM15 possesses a cytoplasmic tail with potential recognition sites for several protein kinases20 that are known to be major players in signal transduction. These unique features provide a structural basis for ADAM15 to exert pleiotropic functions via distinct mechanisms. In this study, we tested whether protease shedding of VE-cadherin, disintegrin-mediated disruption of focal adhesion, or intracellular signal transduction via Src and extracellular signal-regulated kinase (ERK) 1/2 played a relatively important role in ADAM15-induced permeability responses in human endothelial cells in the presence and absence of inflammatory stimulation by thrombin.

We also examined the effect of altered ADAM15 expression on endothelial permeability because recent studies indicate that ADAM15 upregulation is functionally involved in pathological angiogenesis21 and tumour metastasis.22 Moreover, ADAM15 is upregulated in cells treated with pro-inflammatory cytokines23 and in tissues of inflammatory diseases such as atherosclerosis,24 rheumatoid arthritis,25 and irritable bowels,26 indicating the possibility that increased ADAM15 serves as an inflammatory mediator.11 However, the specific role of ADAM15 in regulating VE permeability has not been established, and even less is known about its mechanism of action. Therefore, characterization of the molecular basis underlying ADAM15-induced permeability responses would be important for a further understanding of inflammatory diseases.

2. Methods

2.1 Transfection

Plasmid pcDNA/human WT ADAM15 with haemagglutinin tag at the C-terminus was generated as previously described.18 Mutant ADAM15 cDNA producing a catalytically dead metalloproteinase was constructed by mutating the glutama into alanine at 350 (E350A).18 Human umbilical vein endothelial cells (HUVECs) (Combrex, MD, USA) were maintained in endothelial growth medium (Lonza, NJ, USA). Transient transfection of siRNA (Santa Cruz, CA, USA) or pcDNA constructs was achieved by using Nucleofector II (Amaxa Biosystems, Cologne, Germany).

2.2 Cell treatment and immunoblotting

All measurements were made 72 h post-transfection. To examine the signalling role of ERK1/2 or Src, cells were starved overnight and treated with vehicle, 10 µM U0126, or PP2 (Calbiochem, CA, USA) for 1 h. Then phospho (Thr202/Tyr204)- and total ERK1/2 were monitored with specific antibodies (Cell Signaling, MA, USA). To test VE-cadherin shedding, cells were treated with the γ-secretase inhibitor DAPT (10 µM) for 16 h followed by western blotting using an anti-VE-cadherin C-terminus antibody (Santa Cruz, CA, USA). Cells were lysed with RIPA buffer and protein concentration determined by BCA assay. Cell lysates corresponding to 20 µg protein were submitted to western blotting as previously described.27 When necessary, stripping buffer (Thermo, VT, USA) was applied to the same membrane for reprobing.

2.3 Albumin transendothelial flux

Albumin flux across cultured HUVEC monolayers was measured as previously described.27 Briefly, 105 HUVECs were grown to confluence on a transwell membrane (Corning, NY, USA). FITC-labelled albumin (15 µM) was added to the top chamber in the presence or absence of 25 nM thrombin. After 1 h incubation, concentrations of albumin in the top and bottom chambers were monitored with a fluorescence microplate reader (BioTek, VT, USA). The permeability coefficient of albumin (Pa) was determined as Pa = [A]/t × 1/A × V/[L], where [A] is the bottom chamber concentration, t the time (s), A the area of the membrane (cm2), V the bottom chamber volume, and [L] the top chamber concentration. At the same time, parallel wells were submitted to MTT (Roche, CA, USA) assay and Calcein AM (Invitrogen, CA, USA) staining to confirm cell quantity and confluence of the monolayers.

2.4 Transendothelial electrical resistance (TER)

As an indicator of cell–cell and cell–matrix adhesive barrier properties, transendothelial electrical resistance (TER) was measured as previously described.27 Briefly, 105 cells were seeded onto ECIS electrode arrays (Applied Biophysics, NY, USA) and grown overnight. With a 1 V, 4000 Hz alternating current signal supplied through a 1 MΩ resistor to a constant-current source, in-phase voltage, and out-of-phase voltage were recorded with ECMS 1.0 software (CET, IA, USA). Endothelial barrier function was expressed as TER normalized to the baseline and the time when thrombin added was set at 0. Only endothelial monolayers with a baseline TER of 5000 Ω or higher were used for experiments in this study.

2.5 Neutrophil transmigration

HUVECs (5 × 104) were seeded onto a 96-well transwell membrane (Millipore, CA, USA) and grown overnight to confluence. Human neutrophils were isolated from peripheral blood based on approval by the University of California at Davis Institutional Review Board and the investigation conforms to the Declaration of Helsinki. Neutrophils were separated with histopaque (Sigma, MO, USA) gradient centrifugation followed by negative selection (Stem Cell, BC, Canada) which yielded a purity >90%. 5 × 104 neutrophils were added to the top well with or without 10 nM fMLP (Sigma, MO, USA) in the bottom well. After a 2 h incubation, 5 × 104 polystyrene beads (Polysciences, PA, USA) were added to the bottom well and then migrated neutrophils were counted using FACS and normalized to 5000 beads. In parallel, the wells were submitted to MTT assay and Calcein AM staining to confirm cell quantity and confluence.

2.6 Conditioned medium analysis

Serum-free medium was collected and processed as described previously.18 The level of soluble VE-cadherin was detected using western blotting with an antibody against the extracellular domain of VE-cadherin (R&D, MN, USA).

2.7 Statistical analysis

For each intervention, multiple experiments were performed and data presented as mean ± SD. The number of samples (n) indicates the number of experiments done in separate days using different cells. Two-tailed unpaired Student's test was used for comparison between two groups and one-way analysis of variance used for multiple groups to evaluate the level of difference. Significance was accepted at P ≤ 0.05.

3. Results

3.1 ADAM15 is a regulator of endothelial permeability

Since ADAM15 is upregulated in several inflammatory settings2426 that are associated with endothelial hyperpermeability, we aimed to determine the causal relationship between ADAM15 expression and endothelial permeability in HUVECs. We first verified that pcDNA/ADAM15 transfection increased ADAM15 expression by ∼60% and siRNA/ADAM15 knockdown reduced its expression by ∼85% (Figure 1A). Next, albumin permeability and electric resistance were measured in ADAM15-overexpressing or knockdown HUVECs. Thrombin, a permeability-increasing agonist contributing to vascular inflammation,28 was used to stimulate the endothelial monolayers. In non-stimulated monolayers, ADAM15 overexpression resulted in a 35% increase, whereas knockdown caused a rather small (16%) decrease, in albumin permeability (Figure 1B), supporting the possibility that ADAM15 contributes to vascular barrier dysfunction under conditions where this molecule is upregulated. Furthermore, when thrombin was added, augmented hyperpermeability was observed in ADAM15-overexpressing cells (37% increase). Accordingly, ADAM15 knockdown caused a 20% decrease in Pa in the presence of thrombin (Figure 1B), indicating a role for ADAM15 in mediating thrombin-induced hyperpermeability. Consistent with the albumin permeability assay, the TER dynamics showed a rapid drop in resistance (indicative of barrier dysfunction) upon thrombin. Overexpression of ADAM15 augmented the decrease in TER (maximal resistance −0.39 in mock-transfected control vs. −0.48 in ADAM15 overexpression) (Figure 1C). In contrast, ADAM15 knockdown attenuated thrombin-induced decreases in TER (−0.40 in scrambled siRNA control vs. −0.26 in siRNA ADAM15) (Figure 1C). These results demonstrate that ADAM15 overexpression increases endothelial permeability and it also contributes to thrombin-induced hyperpermeability.

Figure 1

ADAM15 regulates endothelial permeability. (A) Western blot analysis of ADAM15 expression in HUVECs non-tranfected (NT) or transfected with empty vector (mock), ADAM15 siRNA (siADAM15), scrambled siRNA (siScam), pcDNA/WT ADAM15 (ovrexp/WT). Top, representative blots; bottom, quantitative protein levels (n = 8). *Indicates P < 0.05 vs. mock or NT. (B) Albumin permeability (Pa) measured by the ratio of transendothelial flux to concentration difference in ADAM15-overexpressing (ovrexp/WT) or knockdown (siADAM15) HUVECs in the absence (solid) or presence (open) of thrombin (25 nM, 60 min) (n = 3). *P < 0.05 vs. mock or NT (right) without thrombin; #P < 0.05 vs. mock or NT with thrombin. (C) Transcellular electric resistance (TER) was measured in HUVECs as indicator of adhesive barrier function before and after thrombin (25 nM). Top, averaged peak response (n = 4). *P < 0.05 vs. mock or NT. Bottom, individual tracings showing the TER dynamic. Time 0 indicates the time when thrombin was added.

3.2 ADAM15 does not cause VE-cadherin shedding

It has been shown that ADAM15 and ADAM10 shed E- and N-cadherins on the surface of epithelial and neuronal cells.18,29 In endothelial cells, ADAM10 cleaves VE-cadherin thus facilitating T-cell transmigration.19 These findings along with the suggestion that ADAM15 co-localizes with VE-cadherin30 promoted us to test whether ADAM15 affected endothelial permeability by digesting VE-cadherin. We transfected cells with a cDNA mutant that produces dominant expression of a catalytically dead metalloproteinase.18 Our data, however, suggested that the protease activity was not involved in VE-cadherin shedding or degradation. As shown in Figure 2A, expression of either WT or catalytically incompetent ADAM15 did not alter the level of soluble VE-cadherin in the extracellular medium (indicator of ectodomain shedding). Likewise, ADAM15 knockdown and overexpression produced the same level of soluble VE-cadherin. Further, there was no difference in the production of the C-terminal fragment (CTF) of VE-cadherin in cells expressing WT and mutant ADAM15 or depleted of ADAM15 after treatment with the γ-secretase inhibitor DAPT which prevents secondary degradation and CTF removal (Figure 2B). Consistently, the functional assays showed that the expression of WT ADAM15 with intact protease function or ADAM15 mutant lacking protease activity increased albumin permeability and TER response to thrombin to a similar extent (Figure 2C), indicating that the protease activity is not required for ADAM15-induced hyperpermeability.

Figure 2

ADAM15-induced permeability is independent of its proteolytic effect on VE-cadherin shedding. (A) The level of soluble VE-cadherin measured by immunoblotting with an antibody against the extracellular domain of VE-cadherin in conditioned media. Full-length VE-cadherin (FL VE-cad) was measured in cell lysate as control. No difference detected in cells overexpressing ADAM15 wild-type (ovrexp/WT) and its mutant lacking protease function (ovrexp/mut) (n = 3). (B) Detection of VE-cadherin shedding products by immunoblotting with an antibody specific to the C-terminal fragment (CTF) of VE-cadherin in cells treated with the γ-secretase inhibitor DAPT. There is no difference in CTF production from cells expressing wild-type and catalytically dead ADAM15 (n = 3). (C) Comparison of ADAM15 level and permeability in HUVECs overexpressing ADAM15 wild-type (ovrexp/WT) and its mutant lacking protease function (ovrexp/mut). Left column shows consistent levels of ADAM15 expression regardless of mutation (n = 6). *P < 0.05 vs. mock cells. Middle column shows that ADAM15 WT or mutant increases albumin permeability and enhances thrombin-induced barrier dysfunction. *P < 0.05 vs. mock; #P < 0.05 vs. mock with thrombin (n = 3). Right column shows representative TER dynamics from three experiments.

3.3 ADAM15 affects neutrophil transendothelial migration

We further determined the effect of endothelial ADAM15 on neutrophil transendothelial migration in the absence and presence of a chemoattractant, fMLP. In the absence of fMLP, expression of either WT or mutant ADAM15 in HUVECs increased neutrophil transmigration by two- to three-folds. In the presence of fMLP, WT and mutant ADAM15 caused a further increase in transmigration by more than 30% (Figure 3A). Knockdown of ADAM15 produced an opposite effect, reducing neutrophil transmigration with or without fMLP (Figure 3B).

Figure 3

ADAM15 promotes neutrophil transendothelial migration with and without chemoattractant. HUVECs expressing ADAM15 WT or mutant were grown on transwell membrane with neutrophils added to the top chamber and fMLP or vehicle added to the bottom. Transmigrated neutrophils were counted using FACS and normalized to the mock or non-treated condition. Top, transmigration across ADAM15 WT and mutant expressed HUVECS without (−) and with (+) fMLP (n = 3). Bottom, transmigration across ADAM15 knockdown and control siRNA treated HUVECs with or without fMLP (n = 3). *P < 0.05 vs. mock or NT cells without fMLP. #P < 0.05 vs. mock or NT with fMLP.

3.4 ADAM15 activates ERK1/2 signalling independently of its protease activity

Because ERK1/2 phosphorylation is involved in permeability regulation by thrombin31 and other inflammatory mediators like histamine,32 we assessed whether ERK1/2 signalling contributed to the ADAM15 effect. In the absence of thrombin, overexpression of either WT or mutant ADAM15 increased ERK1/2 phosphorylation by nearly two-fold, whereas knockdown of ADAM15 decreased the phosphorylation by 30% (Figure 4A). When cells were stimulated with thrombin, overexpression (WT or mutant) further elevated ERK1/2 phosphorylation and knockdown produced an opposite effect (Figure 4A). The experiment using U0126, which blocks ERK1/2 activation, further supports the involvement of ERK1/2 signalling in ADAM15-mediated permeability. As shown in Figure 4B, while U0126 had no effect on the basal barrier properties of mock-transfected endothelial monolayers, it prevented ADAM15-induced increase in albumin permeability. Furthermore, U0126 pre-treatment inhibited thrombin-induced hyperpermeability; the inhibitory effect was more significant in ADAM15-overexpressing cells than in seen mock-transfected cells (Figure 4C). These data demonstrate an important role of ERK1/2 signalling in ADAM15 regulation of endothelial barrier function.

Figure 4

ADAM15 causes ERK1/2 phosphorylation coupled with hyperpermeability. (A) ERK1/2 phosphorylation (pERK1/2) was measured by blotting with anti-phospho ERK1/2 (T202/Y204) in HUVECs expressing ADAM15 WT or mutant in the absence and presence of thrombin (25 nM, 5 min). Total ERK1/2 (tErk1/2) was probed as control. Top, representative blots. Bottom, ratio of phosphorylated to total ERK1/2 (n = 5). *P < 0.05 vs. mock or NT without thrombin; #P < 0.05 vs. mock or NT with thrombin. (B) ERK1/2 phosphorylation (top) and albumin permeability (bottom) in ADAM15-overexpressing HUVECs during inhibition of ERK activation with UO126 (10 µM, 60 min). The inhibitor blocks ADAM15-induced increase in Pa (n = 3). *P < 0.05 vs. mock with vehicle; #P < 0.05 vs. ovrexp with vehicle. (C) ERK1/2 phosphorylation (top) and thrombin-induced TER changes (bottom) in ADAM15-overexpressing HUVECs with or without inhibition of ERK activation. ADAM15 overexpression enhances the TER decrease by thrombin and the effect is inhibited by UO126 (n = 3). *P < 0.05 vs. mock with vehicle; #P < 0.05 vs. ovrexp with vehicle.

3.5 ADAM15-induced ERK1/2 activation requires Src but not focal adhesion kinase

ERK1/2 phosphorylation has been shown as a downstream event of focal adhesion kinase (FAK) or Src signalling.33,34 With an RGD sequence in its disintegrin domain, ADAM15 can bind αvβ3 and α5β1 integrins35 triggering outside-in signalling via FAK phosphorylation. We tested whether this pathway was responsible for ADAM15-induced ERK1/2 activation and barrier dysfunction. When adhered to collagen, fibronectin, or vitronectin (via different integrins), endothelial cells overexpressing WT or mutant ADAM15 displayed a slightly higher level of FAK phosphorylation at tyrosine 925 compared with mock-transfected cells (data not shown). However, depletion of FAK using siRNA had no effect on ADAM15-induced ERK1/2 activation (Figure 5A), indicating that FAK is not required for the response. In contrast, when Src activity was inhibited by PP2, a significant attenuation in ERK1/2 phosphorylation was observed (Figure 5B). Similar to U0126, PP2 was able to block the hyperpermeability induced by ADAM15 overexpression (Figure 5B).

Figure 5

ADAM15-induced ERK1/2 activation is not dependent on FAK but involves Src signalling. (A) siRNA knockdown (siFAK) depletes total FAK expression (tFAK) but fails to alter ADAM15-induced ERK phosphorylation. Top, representative blots of ERK phosphorylation, total ERK, and total FAK. Bottom, ratio of phospho-ERK to total ERK (n = 3). *P < 0.05 vs. mock. (B) The effect of Src inhibition by PP2 (10 µM, 60 min) on ERK1/2 phosphorylation and hyperpermeability in HUVECs overexpressing ADAM15. Top, representative blots of ERK1/2 phosphorylation. Middle, ratio of phospho- to total ERK1/2 (n = 3). Bottom, albumin permeability (n = 3). *P < 0.05 vs. mock with vehicle; #P < 0.05 vs. ovrexp with vehicle.

3.6 Src and ERK1/2 are involved in ADAM15-facilitated neutrophil transmigration

Pre-treatment of endothelial cells with PP2 reduced neutrophil transmigration and the inhibitory effect was more significant in ADAM15 overexpressing cells than in mock-transfected cells (50 vs. 22% reduction). Pre-treatment of HUVECs with U0126 also attenuated the migration response but the effect was relatively modest (reduction by 10% in mock-transfected and 22% in ADAM15-expressing cells) (Figure 6).

Figure 6

Src and ERK1/2 mediate ADAM15 effect on neutrophil transmigration. Neutrophil chemotactic migration across HUVEC monolayers is enhanced during ADAM15 overexpression compared with mock expression; this effect is greatly attenuated by the Src inhibitor PP2 (10 µM, 60 min) and the ERK pathway inhibitor UO126 (10 µM, 60 min) (n = 3). *P < 0.05 vs. mock with vehicle; #P < 0.05 vs. ovrexp with vehicle.

4. Discussion

ADAM15 is upregulated in endothelial cells treated with pro-inflammatory cytokines23 and in tissues under various inflammatory settings, including atherosclerosis, rheumatoid arthritis, and irritable bowels.2426 In this study, we report that overexpression of ADAM15 in endothelial cells increases endothelial permeability and promotes neutrophil transmigration. Furthermore, ADAM15 enhances endothelial hyperpermeability to thrombin, and ADAM15 depletion attenuates thrombin-induced barrier dysfunction. The mechanism by which ADAM15 regulates permeability is not dependent on its proteolytic domain-mediated shedding of VE-cadherin or its disintegrin effect on cell–matrix focal adhesion; rather, it involves activation of Src and ERK1/2, perhaps via intracellular signalling. Our results have characterized ADAM15 as a novel endothelial barrier regulator and a potential therapeutic target of vascular inflammation.

This study indicates a role of ADAM15 in the pathological regulation of endothelial permeability in diseased vasculature where ADAM15 is upregulated or inflammatory mediators such as thrombin are elaborated. In particular, ADAM15 overexpression was capable of increasing albumin flux and augmenting thrombin-induced barrier dysfunction in endothelial cells. While alterations in the basal barrier property can contribute to enhanced or attenuated response to a stimulus, the effect of ADAM15 on resting endothelial cells was relatively modest compared with that seen with thrombin. In other words, altered basal permeability did not fully account for the altered thrombin response. Alternatively, ADAM15 may serve as a signalling molecule that mediates the permeability response under stimulated conditions. Such a condition is often seen in diseases associated with vascular inflammation or thrombosis where thrombin metabolism or signalling is altered. For example, in atherosclerosis, ADAM15 upregulation in the vascular endothelium may lead to endothelial hyperpermeability and augmented response to thrombin, contributing to the development of lesions. Further investigation with in vivo models of disease or genetically altered mice would provide physiologically significant information.

Based on the complex structure of the ADAM family, multiple molecular pathways have been proposed to explain their effects, of which the best recognized mechanism is proteolytic cleavage or ectodomain shedding of transmembrane molecules via its metalloproteinase domain. We first tested the hypothesis that ADAM15 induced hyperpermeability by shedding of VE-cadherin. Supporting this is that shedding of membrane-anchored VE-cadherin by metalloproteinases, measured as increased soluble fragments corresponding to the extracelluar domain of VE-cadherin, is detected in vascular inflammatory disease.36 As a member of the metalloproteinase family, ADAM15 sheds E-cadherin on the epithelial cell surface generating soluble fragments that trigger ErbB activation.18 ADAM10, a close relative of ADAM15, cleaves VE-cadherin in association with endothelial permeability.19 To our surprise, however, the data from the current study challenges the conventional concept that ADAMs act mainly through proteolysis. We found that ADAM15 with or without protease activity caused barrier responses to a similar extent, and they did not alter the level of soluble VE-cadherin or its degradation products, indicating that VE-cadherin shedding is not involved in ADAM15-induced permeability.

We then examined the potential importance of integrin-mediated focal adhesion in the ADAM15 effect. The extracellular part of ADAM15 contains an RGD sequence that binds to different integrins mediating heterotypic cell interactions.23,35 Overexpression of ADAM15 in epithelial cells facilitates leucocyte adhesion by mechanisms involving its RGD motif.37 Loss of ADAM15 in prostate tumour cells reduces their ability to adhere and migrate.22 In agreement with these studies, we found increased neutrophil transmigration across ADAM15-overexpressed endothelial cells. However, our results do not support the disintegrin effect (disruption of focal adhesion) as a critical step in the endothelial response to ADAM15, since ADAM15 overexpression did not alter integrin expression or cell attachment to different matrix proteins (data not shown). More importantly, siRNA depletion of FAK, a major mediator of integrin signalling, did not significantly alter ADAM15-induced endothelial responses, indicating that FAK is dispensable. Indeed, both RGD-dependent and -independent pathways have been proposed for ADAM15 action. An earlier study with NIH3T3 cells38 suggests that ADAM15 does not alter cell–matrix interactions but functions as a cell–cell adhesive molecule to decrease cell permeability. The discrepancy in the data on permeability is not surprising given the pleiotropic functions and heterogeneous effects of ADAM15 in different cells or tissues. Its effect on the endothelial barrier may not be the same as that seen with cells that do not form barriers or cells connecting to each other via other adhesion molecules than VE-cadherin, which is predominantly expressed in endothelial cell–cell junctions and serves as an important regulator of vascular permeability.

The negative finding about VE-cadherin shedding and focal adhesion disruption promoted us to explore the potential mechanism of intracellular signal transduction. ADAM15 possesses a cytoplasmic tail containing SH3/SH2 binding sequences and putative recognition sites for protein kinases20 capable of transducing complex signals or serving as molecular scaffold to recruit signalling components with kinase activity, such as Src, which in turn act on the endothelial barrier structure.39 In haematopoietic cells, the cytoplasmic tail of ADAM15 binds to Src in a phosphorylation-dependent manner.40 Mutation studies demonstrate the involvement of this cytoplasmic domain in homotypic aggregation of T cells as well as in heterotypic adhesion between lymphocytes and epithelial cells.37 Moreover, several isoforms of ADAM15 have been classified based on splicing variants of the cytoplasmic domain. One variant containing Src binding site with a high catalytic activity dependent on Src has been associated with malignant tumour behaviour.41 While these findings support in general the role of Src in the ADAM15 pathway, our data characterize the specific contribution of Src to endothelial responses to ADAM15. In another study, we found that truncation of its intracellular domain blocked ADAM15-induced increase in permeability, further supporting that intracellular signal transduction as an important mechanism underlying the endothelial effect of ADAM15.

ERK1/2 signalling has long been implicated in endothelial responses to growth factors and inflammatory mediators.31,32 In breast cancer cells, ADAM15 deletion decreases ERK1/2 phosphorylation impairing migration and proliferation.18 In this study, we demonstrate that ADAM15 overexpression stimulates ERK1/2 phosphorylation, an effect responsible for altered barrier function in the presence or absence of inflammatory stimulation. Furthermore, ADAM15-induced ERK1/2 activation is involved in neutrophil transendothelial migration, consistent with a previous observation.42 While ERK1/2 is known to be activated downstream from FAK33 and Src,34 we show that ADAM15-induced ERK1/2 activation is not dependent on FAK but largely through Src. This finding supports our hypothesis that the Src-binding cytoplasmic domain of ADAM15 serves as a triggering factor in the transduction of permeability responses. Further, additional signalling molecules may be involved in the ADAM15 pathway because Src inhibition did not completely block the phosphorylation response.

The precise mechanisms by which Src or ERK1/2 regulates permeability remain to be elucidated. We hypothesize that these kinases can target the endothelial barrier structure for phosphorylation rendering weakened cell–cell adhesion. Our previous studies suggest that Src causes β-catenin tyrosine phosphorylation leading to intercellular gap formation,39 and that the ERK1/2 pathway mediates microvascular hyperpermeability by activating endothelial contractile cytoskeleton and altering cell–cell and cell–matrix interactions.32 A search of potential ERK targets using the consensus phosphorylation motif TXY produces several proteins that are known to be essential to endothelial barrier function, including FAK, VE-cadherin, catenins, actin, and actin-binding proteins.32 Although siRNA knockdown of FAK did not effectively abolish the permeability effect of ADAM15, we cannot rule out the possibility that post-translational modification of FAK activity or perturbation of integrin signalling contributes to the ADAM15 action. Some studies have shown a link between integrin activity and Src kinases.43,44 Likewise, while VE-cadherin shedding was not detected, it is possible that ADAM15 induce phosphorylation or conformational changes of the junction complex.

We also examined the effect of endothelial ADAM15 on neutrophil transendothelial migration because neutrophil diapedesis often occur in parallel with endothelial barrier dysfunction during vascular inflammation. Neutrophils migrate across the endothelium via paracellular pathways maintained by junctional molecules including VE-cadherin, PECAM-1, and JAM-A.4 Despite the current focus on VE-cadherin, we recognize the role of PECAM-1 and JAM-A in regulating endothelial integrity and neutrophil transmigration and their potential involvement in the ADAM15 pathway. Additionally, the relative contribution of endothelial barrier properties vs. neutrophil activities to the transmigration process requires further studies. Within this context, the result that ADAM15 greatly increased neutrophil transmigration without a chemoattractant indicate the possibility that endothelial activation is sufficient to open or loosen the barrier for transmigration. Further stimulation or activation of neutrophils can augment the migration response but may not a prerequisite for the overall process. This may explain why the chemotactic migration to fMLP was not increased much more than the non-chemotactic migration. The data support an active role of endothelial ADAM15 in vascular inflammation.

In conclusion, our study has identified ADAM15 as a novel endothelial barrier regulator especially under inflammatory stimulation. The effects of ADAM15 on endothelial hyperpermeability and neutrophil transmigration are not dependent on the catalytic activity of the metalloproteinase but are mediated by intracellular signalling involving Src and ERK1/2 activation.

This work was supported by the National Institutes of Health grants HL61507, HL84542, and HL96640.

We thank Chris D. Pivetti, Robert L. Pitts, Olesya P. Litovka, and Bert J. Frederich for excellent technical assistance.

Conflict of interest: none declared.

View Abstract


CHE University Ranking 2015/16

Germany's largest University Ranking

Register free of charge

More than 30
subject areas
More than 300 universities
Individual Ranking
To use the ranking, a registration is required.
  • FAQ

    Simply click on the most frequently asked questions regarding the ranking to get the answers.

    Which subjects were examined and when?
    The data for the single subjects are actualised in a three-year circle: natural sciences, mathematics, computer science, medicine, nursing, sports 2015. Law, economics, social sciences, social work 2014; humanities, psychology, peadagogy 2013.
    Why is the data not updated every year?
    The enormous amount of work necessary for such a complex ranking makes a yearly update of the data for all subjects impossible. This would be beyond our capacities and the capacities of the universities, which assist with a considerable amount of preparatory work for the ranking project. Except for a few individual cases, changes at universities do not take place with the speed that would make an annual update necessary. In addition, most cases do not show any values referring to one year, but average values across several years (e.g. publications, study time). The figure-work of these values is unlikely to seriously change within one year. In addition, it is extremely unlikely that there would be substantial changes, e.g. for publications or the duration of studies within one year. The time comparison in the different subjects, which was possible for the first time in the 2003 ranking, also shows that important changes, which really result in a change to the ranking groups, are more an exception than a rule.
    Why is my subject not included?
    The subjects included in the ranking cover the degree courses of around 80% of first-year students. The subjects that are not included are, for the most part, subjects that are only offered at a few universities, or for which only a relatively small number of students per university have enrolled.
    When will the new ranking be available?
    The CHE UniversityRanking 2015/16, for which the natural sciences, mathematics, computer sciences, medicine, nursing and sports were examined was published in the spring of 2015. For further information on this project see
    What does Research Reputation / Reputation for Academic Studies and Teaching tell?
    Currently, the CHE Ranking includes the indicator "Research Reputation" and "Reputation for Academic Studies and Teaching" only for a few subjects. The indicator is displayed for the following subjects: Business Administration, Civil Engineering, Bioengineering, Chemical Engineering, Electrical Engineering and Information Engineering, Facility Management, German Language and Literature, Law, Mechanical Engineering, Medicine, Psychology, Romance Studies, Environmental Engineering, Economics, Mechanical-, Process- and Chemical Engineering and Material Engineering. The indicator reflects the faculties' reputation among the professors of the subject. For the Reputation for Academic Studies and Teaching, the CHE asks the professors which universities in their opinion are best for studying their subject, if only the quality of the education was of importance. For the Research Reputation the professors are asked, which universities they consider as "leading" in their subject. Within the subject community, there is, as a rule, a clear picture about the standing or the reputation of the individual faculties. Even if the professors do not know all the faculties of their subject in detail, there is nevertheless this reputation hierarchy in their heads. This indicator reflects the opinion of the professors; it is not an indicator of the universities' efficiency! A faculty's reputation may, but does not have to, match its factual achievements in research and teaching. There may be faculties, which still live off achievements from the past; but vice versa, there are also faculties, whose achievements are not yet recognised among the professors. Nevertheless, this indicator may be meaningful information - not least as the reputation of a university is also linked to the graduates.
    Does the ranking only cover subjective opinions about the universities?
    Why does the ranking not include any survey of employers?
    Which indicators are selected for the "Compact Ranking"?
    Are students' opinions soft indicators?
    In addition to facts about various areas, the higher education ranking contains a number of student opinions. In contrast to the frequently uttered opinion that they are purely "Well-being indicators", they are perfectly meaningful, provided the questions are asked with sufficient detail. On the one hand, previous years have shown that students and professors judge at different levels of grades - professors usually around one grade better than students - but the relative order of faculties is not very different, the correlation of opinions is - according to indicator and subject - at around 0.5 to 0.8. Therefore, a library regarded as poor in the eyes of students is usually also given poor assessments by professors. On the other hand, repeated examinations of the same subject show that students' opinions hardly change at most universities. Actual improvements, however, such as a faculty moving into new premises, are clearly reflected here; a sign that students do assess according to objective criteria.
    What are bibliometrics and how does CHE do it?
    Can research achievement be measured?
    Where in Germany can I study which course?
    In the Compact Ranking, all universities offering a course in a certain subject are listet. You may also use the search-fuction.
    Courses and subjects not listed can be found at the DAAD University Guide published in cooperation with the German Rectors'' Conference
    Can conclusions be drawn from the results of the CHE UniversityRanking student questionnaires regarding the quality of the graduates from a HEI?
    Why is there no ranking of master programmes?
    In Master programs the number of enrolled students is often too small to achieve an adequate return rate. Nevertheless, it is possible to survey the Master students in some fields. Master students in Electrical Engineering and Information Engineering and Mechatronics have been surveyed in 2013 and students in Business Administration and Economic Sciences in 2014. The results of the Masters student's survey in Computer Sciences will be published in autumn 2015.


Figure 2: TLC/FID chromatograms of lipid classes in a standard and as part of a study of the effects of produced water from oil and gas production on cod [17]. Lipid class composition was determined after a three-step development on Chromarods (Figure 1). Lipid extracts were applied to the Chromarods and focused to a narrow band using 100% acetone. The first development system was hexane : diethyl ether : formic acid (98.95 : 1.0 : 0.05). The rods were developed for 25 min, removed from the solvent system for 5 min, and replaced for 20 min and then partially scanned in the Iatroscan. The second development was for 40 min in hexane : diethyl ether : formic acid (79 : 20 : 1) after which the rods were partially scanned. The final separation had two steps, the first was development in 100% acetone for two 15 min time periods, then two 10 min periods in chloroform : methanol : chloroform-extracted water (5 : 4 : 1), after which the rods were dried and their entire length scanned. Before using each solvent system the rods were placed in a constant humidity chamber. The Chromarods were calibrated using standards (e.g., Figure 1) from Sigma Chemicals (Sigma Chemicals, St. Louis, MI, USA).


5 questions for Transformers leader Optimus Prime

Optimus Prime

By Michelle Mills

As Transformers fans flooded onto the floor of BotCon 2014, the official Hasbro Transformers’ collection convention, at the Pasadena Convention Center last weekend, we wrangled a few minutes with the leader of the Autobots, Optimus Prime. Actually, our interview was with John Barber, editor of IDW Publishing and writer of “Transformers: Robots in Disguise” and other comic books, who offered to speak for the character he knows so well.

Q: Why are the Autobots mad at humans?

A: As much as we try to protect the humans, they see all of us as one group and it’s important to understand that everyone is an individual and the choices we make are the choices that define us.

Q: Will you accept the artificial Transformers the humans have created?

A: As with anyone, those Autobots will have to prove themselves. I hold nothing against where someone came from or how they were created. It depends again, as I said, on the choices they make and the life they decide to lead.

Q: Does it hurt to transform from robot to car and vice versa?

A: Not at all, it feels great. If you’re tired or have been in a fight, it might hurt a little bit, but first thing in the morning, it’s nice.

Q: What do Transformers eat?

A: Energon is our sustenance and our lifeblood. It’s a pure form of energy found on Cybertron and rarely in other places in the galaxy... We’re fuel-efficient and we’re green.

Q: What advice would you give humans?

A: The most important thing is to remember that freedom is the right of all sentient beings, and to allow everyone to live the life that they choose to live and not force your will on others.


Aaron Hernandez filed a grievance to get $6 million plus in salary from the New England Patriots. But his being indicted for a July 2012 double murder on Thursday means that grievance no longer holds much water.

Because that incident happened before Hernandez signed his mega contract extension later in '12, it goes against language in his contract regarding "existing circumstances". That's according to's Joel Corry, a former NFL agent who detailed the cap situation with Hernandez and the Patriots in January.

It would give the New England organization grounds to recoup what they owed Hernandez, including a $3.25 million singing bonus that was deferred and paid only in March of this year. That matches the minimal extra salary-cap relief the Patriots would get, too.


What is Electricity?

Contributors: Jimb0
Favorited Favorite 5

Getting Started

Electricity is all around us–powering technology like our cell phones, computers, lights, soldering irons, and air conditioners. It’s tough to escape it in our modern world. Even when you try to escape electricity, it’s still at work throughout nature, from the lightning in a thunderstorm to the synapses inside our body. But what exactly is electricity? This is a very complicated question, and as you dig deeper and ask more questions, there really is not a definitive answer, only abstract representations of how electricity interacts with our surroundings.

Public domain NOAA lightning picture

Electricity is a natural phenomenon that occurs throughout nature and takes many different forms. In this tutorial we’ll focus on current electricity: the stuff that powers our electronic gadgets. Our goal is to understand how electricity flows from a power source through wires, lighting up LEDs, spinning motors, and powering our communication devices.

Electricity is briefly defined as the flow of electric charge, but there’s so much behind that simple statement. Where do the charges come from? How do we move them? Where do they move to? How does an electric charge cause mechanical motion or make things light up? So many questions! To begin to explain what electricity is we need to zoom way in, beyond the matter and molecules, to the atoms that make up everything we interact with in life.

This tutorial builds on some basic understanding of physics, force, energy, atoms, and fields in particular. We’ll gloss over the basics of each of those physics concepts, but it may help to consult other sources as well.

Going Atomic

To understand the fundamentals of electricity, we need to begin by focusing in on atoms, one of the basic building blocks of life and matter. Atoms exist in over a hundred different forms as chemical elements like hydrogen, carbon, oxygen, and copper. Atoms of many types can combine to make molecules, which build the matter we can physically see and touch.

Atoms are tiny, stretching at a max to about 300 picometers long (that’s 3x10-10 or 0.0000000003 meters). A copper penny (if it actually were made of 100% copper) would have 3.2x1022 atoms (32,000,000,000,000,000,000,000 atoms) of copper inside it.

Even the atom isn’t small enough to explain the workings of electricity. We need to dive down one more level and look in on the building blocks of atoms: protons, neutrons, and electrons.

Building Blocks of Atoms

An atom is built with a combination of three distinct particles: electrons, protons, and neutrons. Each atom has a center nucleus, where the protons and neutrons are densely packed together. Surrounding the nucleus are a group of orbiting electrons.

Rutherford atom model

A very simple atom model. It’s not to scale but helpful for understanding how an atom is built. A core nucleus of protons and neutrons is surrounded by orbiting electrons.

Every atom must have at least one proton in it. The number of protons in an atom is important, because it defines what chemical element the atom represents. For example, an atom with just one proton is hydrogen, an atom with 29 protons is copper, and an atom with 94 protons is plutonium. This count of protons is called the atom’s atomic number.

The proton’s nucleus-partner, neutrons, serve an important purpose; they keep the protons in the nucleus and determine the isotope of an atom. They’re not critical to our understanding of electricity, so let’s not worry about them for this tutorial.

Electrons are critical to the workings of electricity (notice a common theme in their names?) In its most stable, balanced state, an atom will have the same number of electrons as protons. As in the Bohr atom model below, a nucleus with 29 protons (making it a copper atom) is surrounded by an equal number of electrons.

Copper Bohr model

As our understanding of atoms has evolved, so too has our method for modeling them. The Bohr model is a very useful atom model as we explore electricity.

The atom’s electrons aren’t all forever bound to the atom. The electrons on the outer orbit of the atom are called valence electrons. With enough outside force, a valence electron can escape orbit of the atom and become free. Free electrons allow us to move charge, which is what electricity is all about. Speaking of charge…

Flowing Charges

As we mentioned at the beginning of this tutorial, electricity is defined as the flow of electric charge. Charge is a property of matter–just like mass, volume, or density. It is measurable. Just as you can quantify how much mass something has, you can measure how much charge it has. The key concept with charge is that it can come in two types: positive (+) or negative (-).

In order to move charge we need charge carriers, and that’s where our knowledge of atomic particles–specifically electrons and protons–comes in handy. Electrons always carry a negative charge, while protons are always positively charged. Neutrons (true to their name) are neutral, they have no charge. Both electrons and protons carry the same amount of charge, just a different type.

Lithium atom with particle charges labeled

A lithium atom (3 protons) model with the charges labeled.

The charge of electrons and protons is important, because it provides us the means to exert a force on them. Electrostatic force!

Electrostatic Force

Electrostatic force (also called Coulomb’s law) is a force that operates between charges. It states that charges of the same type repel each other, while charges of opposite types are attracted together. Opposites attract, and likes repel.

Charges attract/repel

The amount of force acting on two charges depends on how far they are from each other. The closer two charges get, the greater the force (either pushing together, or pulling away) becomes.

Thanks to electrostatic force, electrons will push away other electrons and be attracted to protons. This force is part of the “glue” that holds atoms together, but it’s also the tool we need to make electrons (and charges) flow!

Making Charges Flow

We now have all the tools to make charges flow. Electrons in atoms can act as our charge carrier, because every electron carries a negative charge. If we can free an electron from an atom and force it to move, we can create electricity.

Consider the atomic model of a copper atom, one of the preferred elemental sources for charge flow. In its balanced state, copper has 29 protons in its nucleus and an equal number of electrons orbiting around it. Electrons orbit at varying distances from the nucleus of the atom. Electrons closer to the nucleus feel a much stronger attraction to the center than those in distant orbits. The outermost electrons of an atom are called the valence electrons, these require the least amount of force to be freed from an atom.

Copper atom with valence electron labeled

This is a copper atom diagram: 29 protons in the nucleus, surrounded by bands of circling electrons. Electrons closer to the nucleus are hard to remove while the valence (outer ring) electron requires relatively little energy to be ejected from the atom.

Using enough electrostatic force on the valence electron–either pushing it with another negative charge or attracting it with a positive charge–we can eject the electron from orbit around the atom creating a free electron.

Now consider a copper wire: matter filled with countless copper atoms. As our free electron is floating in a space between atoms, it’s pulled and prodded by surrounding charges in that space. In this chaos the free electron eventually finds a new atom to latch on to; in doing so, the negative charge of that electron ejects another valence electron from the atom. Now a new electron is drifting through free space looking to do the same thing. This chain effect can continue on and on to create a flow of electrons called electric current.

Simple electron flow

A very simplified model of charges flowing through atoms to make current.

Some elemental types of atoms are better than others at releasing their electrons. To get the best possible electron flow we want to use atoms which don’t hold very tightly to their valence electrons. An element’s conductivity measures how tightly bound an electron is to an atom.

Elements with high conductivity, which have very mobile electrons, are called conductors. These are the types of materials we want to use to make wires and other components which aid in electron flow. Metals like copper, silver, and gold are usually our top choices for good conductors.

Static or Current Electricity

Static Electricity

Static electricity example

Spark gap igniter static shock

Current Electricity

Electric Fields

We have a handle on how electrons flow through matter to create electricity. That’s all there is to electricity. Well, almost all. Now we need a source to induce the flow of electrons. Most often that source of electron flow will come from an electric field.

What’s a Field?

A field is a tool we use to model physical interactions which don’t involve any observable contact. Fields can’t be seen as they don’t have a physical appearance, but the effect they have is very real.

We’re all subconsciously familiar with one field in particular: Earth’s gravitational field, the effect of a massive body attracting other bodies. Earth’s gravitational field can be modeled with a set of vectors all pointing into the center of the planet; regardless of where you are on the surface, you’ll feel the force pushing you towards it.

Earth gravity field

The strength or intensity of fields isn’t uniform at all points in the field. The further you are from the source of the field the less effect the field has. The magnitude of Earth’s gravitational field decreases as you get further away from the center of the planet.

As we go on to explore electric fields in particular remember how Earth’s gravitational field works, both fields share many similarities. Gravitational fields exert a force on objects of mass, and electric fields exert a force on objects of charge.

Electric Fields

Electric fields (e-fields) are an important tool in understanding how electricity begins and continues to flow. Electric fields describe the pulling or pushing force in a space between charges. Compared to Earth’s gravitational field, electric fields have one major difference: while Earth’s field generally only attracts other objects of mass (since everything is so significantly less massive), electric fields push charges away just as often as the attract them.

The direction of electric fields is always defined as the direction a positive test charge would move if it was dropped in the field. The test charge has to be infinitely small, to keep its charge from influencing the field.

We can begin by constructing electric fields for solitary positive and negative charges. If you dropped a positive test charge near a negative charge, the test charge would be attracted towards the negative charge. So, for a single, negative charge we draw our electric field arrows pointing inward at all directions. That same test charge dropped near another positive charge would result in an outward repulsion, which means we draw arrows going out of the positive charge.

Electric fields of single charges

The electric fields of single charges. A negative charge has an inward electric field because it attracts positive charges. The positive charge has an outward electric field, pushing away like charges.

Groups of electric charges can be combined to make more complete electric fields.

Bigger e-field

The uniform e-field above points away from the positive charges, towards the negatives. Imagine a tiny positive test charge dropped in the e-field; it should follow the direction of the arrows. As we’ve seen, electricity usually involves the flow of electrons–negative charges–which flow against electric fields.

Electric fields provide us with the pushing force we need to induce current flow. An electric field in a circuit is like an electron pump: a large source of negative charges that can propel electrons, which will flow through the circuit towards the positive lump of charges.

Electric Potential (Energy)

When we harness electricity to power our circuits, gizmos, and gadgets, we’re really transforming energy. Electronic circuits must be able to store energy and transfer it to other forms like heat, light, or motion. The stored energy of a circuit is called electric potential energy.

Energy? Potential Energy?

To understand potential energy we need to understand energy in general. Energy is defined as the ability of an object to do work on another object, which means moving that object some distance. Energy comes in many forms, some we can see (like mechanical) and others we can’t (like chemical or electrical). Regardless of what form it’s in, energy exists in one of two states: kinetic or potential.

An object has kinetic energy when it’s in motion. The amount of kinetic energy an object has depends on its mass and speed. Potential energy, on the other hand, is a stored energy when an object is at rest. It describes how much work the object could do if set into motion. It’s an energy we can generally control. When an object is set into motion, its potential energy transforms into kinetic energy.

Gravitational potential energy

Let’s go back to using gravity as an example. A bowling ball sitting motionless at the top of Khalifa tower has a lot of potential (stored) energy. Once dropped, the ball–pulled by the gravitational field–accelerates towards the ground. As the ball accelerates, potential energy is converted into kinetic energy (the energy from motion). Eventually all of the ball’s energy is converted from potential to kinetic, and then passed on to whatever it hits. When the ball is on the ground, it has a very low potential energy.

Electric Potential Energy

Just like mass in a gravitational field has gravitational potential energy, charges in an electric field have an electric potential energy. A charge’s electric potential energy describes how much stored energy it has, when set into motion by an electrostatic force, that energy can become kinetic, and the charge can do work.

Like a bowling ball sitting at the top of a tower, a positive charge in close proximity to another positive charge has a high potential energy; left free to move, the charge would be repelled away from the like charge. A positive test charge placed near a negative charge would have low potential energy, analogous to the bowling ball on the ground.

Potential Energy in a field

To instill anything with potential energy, we have to do work by moving it over a distance. In the case of the bowling ball, the work comes from carrying it up 163 floors, against the field of gravity. Similarly, work must be done to push a positive charge against the arrows of an electric field (either towards another positive charge, or away from a negative charge). The further up the field the charge goes, the more work you have to do. Likewise, if you try to pull a negative charge away from a positive charge–against an electric field–you have to do work.

For any charge located in an electric field its electric potential energy depends on the type (positive or negative), amount of charge, and its position in the field. Electric potential energy is measured in units of joules (J).

Electric Potential

Electric potential builds upon electric potential energy to help define how much energy is stored in electric fields. It’s another concept which helps us model the behavior of electric fields. Electric potential is not the same thing as electric potential energy!

At any point in an electric field the electric potential is the amount of electric potential energy divided by the amount of charge at that point. It takes the charge quantity out of the equation and leaves us with an idea of how much potential energy specific areas of the electric field may provide. Electric potential comes in units of joules per coulomb (J/C), which we define as a volt (V).

In any electric field there are two points of electric potential that are of significant interest to us. There’s a point of high potential, where a positive charge would have the highest possible potential energy, and there’s a point of low potential, where a charge would have the lowest possible potential energy.

One of the most common terms we discuss in evaluating electricity is voltage. A voltage is the difference in potential between two points in an electric field. Voltage gives us an idea of just how much pushing force an electric field has.

With potential and potential energy under our belt we have all of the ingredients necessary to make current electricity. Let’s do it!

Electricity in Action!

After studying particle physics, field theory, and potential energy, we now know enough to make electricity flow. Let’s make a circuit!

First we will review the ingredients we need to make electricity:

  • The definition of electricity is the flow of charge. Usually our charges will be carried by free-flowing electrons.
  • Negatively-charged electrons are loosely held to atoms of conductive materials. With a little push we can free electrons from atoms and get them to flow in a generally uniform direction.
  • A closed circuit of conductive material provides a path for electrons to continuously flow.
  • The charges are propelled by an electric field. We need a source of electric potential (voltage), which pushes electrons from a point of low potential energy to higher potential energy.

A Short Circuit

Batteries are common energy sources which convert chemical energy to electrical energy. They have two terminals, which connect to the rest of the circuit. On one terminal there are an excess of negative charges, while all of the positive charges coalesce on the other. This is an electric potential difference just waiting to act!

Battery with charges

If we connected our wire full of conductive copper atoms to the battery, that electric field will influence the negatively-charged free electrons in the copper atoms. Simultaneously pushed by the negative terminal and pulled by the positive terminal, the electrons in the copper will move from atom to atom creating the flow of charge we know as electricity.

Battery short circuit

After a second of the current flow, the electrons have actually moved very little–fractions of a centimeter. However, the energy produced by the current flow is huge, especially since there’s nothing in this circuit to slow down the flow or consume the energy. Connecting a pure conductor directly across an energy source is a bad idea. Energy moves very quickly through the system and is transformed into heat in the wire, which may quickly turn into melting wire or fire.

Illuminating a Light Bulb

Instead of wasting all that energy, not to mention destroying the battery and wire, let’s build a circuit that does something useful! Generally an electric circuit will transfer electric energy into some other form–light, heat, motion, etc. If we connect a light bulb to the battery with wires in between, we have a simple, functional circuit.

Lightbulb animation

Schematic: A battery (left) connecting to a lightbulb (right), the circuit is completed when the switch (top) closes. With the circuit closed, electrons can flow, pushed from the negative terminal of the battery through the lightbulb, to the positive terminal.

While the electrons move at a snails pace, the electric field affects the entire circuit almost instantly (we’re talking speed of light fast). Electrons throughout the circuit, whether at the lowest potential, highest potential, or right next to the light bulb, are influenced by the electric field. When the switch closes and the electrons are subjected to the electric field, all electrons in the circuit start flowing at seemingly the same time. Those charges nearest the light bulb will take one step through the circuit and start transforming energy from electrical to light (or heat).

Going Further

In this tutorial we’ve uncovered just a tiny portion of the tip of the proverbial iceberg. There’s still a ton of concepts left uncovered. From here we’d recommend you step right on over to our Voltage, Current, Resistance, and Ohm’s Law tutorial. Now that you know all about electric fields (voltage) and flowing electrons (current), you’re well on your way to understanding the law that governs their interaction.

Here are some other beginner level concept tutorials we’d recommend reading through:

Or, maybe you’d like to learn something practical? In that case, check out some of these basic level skill tutorials:


Kirkus Reviews QR Code

by D.S. Walker

Pub Date: Nov. 8th, 2010
ISBN: 978-1450260510
Publisher: iUniverse

A family copes with a daughter’s quirks in Walker’s fanciful, heartwarming tale of Asperger’s syndrome.

Like any new parents, Ben Long, a successful Hawaiian pediatrician, and his wife Francesca have high hopes for their first child. Their baby Mia has high hopes for them, too: as a yet-to-be-born spirit in heaven, she noticed Francesca’s kindness and patience and picked her out as her future mom. Mia relies on Francesca’s nurturing qualities because she will be born with Asperger’s syndrome, a mild, often undiagnosed variant of autism. Her parents find her to be a bright, precocious, musical child, but also shy, socially awkward, frightened by new situations and beset with food phobias. What seems to others to be mere eccentricity and cussedness is to Mia a rational response to her unusual cognitive traits. Mia is abnormally sensitive to stimuli: loud voices and bright lights hurt her ears and eyes, new clothes feel like sandpaper, perfume smells like tear gas. While she shrinks from these sensory assaults, her literal-mindedness makes her prone to obsessive anxieties: a news story about tainted hamburger leads to an epic school lunch-room battle and a bird’s nest collected by her grandmother strikes her as a nightmarish tangle of filth and decay. The author sets Mia’s first-person narrative within a larger family story told from Francesca’s point of view as she grapples with Ben’s exasperation over Mia’s problems, tussles with her difficult Chinese-American mother-in-law and weathers the heartache of her parents’ deaths. Writing with a limpid prose style deftly infused with medical research, Walker does a remarkable job illuminating Mia’s offbeat perspective from within; she makes it more a personality than an affliction. The book’s advocacy impulses occasionally overheat, as when Francesca goes ballistic over an incident in which mean girls tease Mia at school. Still, through Mia’s story, Walker dispels much of the mystery of Asperger’s kids while revealing the richness and promise of their lives.

A poignant and enlightening coming-of-age saga.


Haven't found the Essay You Want?
For Only $12.90/page

Should Wealthy Nations Be Required to Share Their Wealth with Poorer Nations by Providing Essay

In recent years, there is a controversial issue is that the rich countries should share their assets among the poorer countries or not. Most of the public agreed that it is a necessary activity to help the poor improve their lives. On the other hand, some tax payers resolutely keep their opinions when they supposed that the governments of poorer nations are liability to take care of their inhabitants by themselves. As a supporter of sharing with the poor, I think that we have many reasons to establish philanthropic organizations to support the wretch in other countries and territories.

Several main reasons will be analyzed in this essay. Beginning with lack of natural resources, poor nations cannot take advantages of fertile soil to cultivate or minerals to exploit. Moreover, weak education causes many consequences, one of them is a large number of residents are illiterate so they cannot approach modern life by knowledge. Because of that, they always live with the shortage of food, clothes and other articles of daily necessities.

They do not have enough money and technology to improve the environment so it brings them to need the help of other countries for surviving. Besides, economic crises occur after several years, as a stage of the economic cycle. Given their capabilities and power, rich nations often recover more quickly than their poor counterparts.

This means that the poor is not only more prone to negative impacts of economic crises but also in more difficult circumstances. In these cases, if we do not join our hands to offer them financial assistance, then the gap between the rich and the poor is become wider, lead to the loss of economic balance. When the living standard has been improved, they can afford to quality good and the trade all over the world will be more prosperous. Last but not least, sharing wealth with the poor is a humanitarian activity, and anyone can do it.

This is the best lesson for children about the important of sharing in hard times. From that, the love of human races will be larger. However, the government of poorer countries should not only rely on others. They also have to improve their own situation by carrying out the reform in education, changing some unsound customs and opening to obtain the knowledge of the world. In conclusion, if the richer can give their wealth and the poorer can improve by themselves, we will soon have a thriving future.

Essay Topics: