Electrical Properties of Cells
Most cell biology is dominated by focusing on biochemistry, but electromagnetic effects also play a crucial role in regulating cell behavior. Cells maintain an electrical potential difference of a few hundred millivolts across their membranes by actively pumping charged particles. A similar potential difference is maintained across mitochondrial membranes. Electric fields seem to play an organizing role in the transport of key molecules within the cell, and in regulating the traffic of molecules between the cytoplasm and the nucleus. Additional important electromagnetic effects are associated with microtubules. The secret electric life of cells remains largely unexplored territory, but it is clear that the progress of cells from healthy to malignant is accompanied by changes in their electromagnetic signatures, thus offering possible diagnostic opportunities, and even the possibility of controlling malignant progression by manipulating electric and magnetic parameters.
Listen to Audio Interviews and Read Transcripts
Audio Interviews and Transcripts from the Workshop
- Interview with Robert Gatenby from the Moffitt Cancer Center in Tampa, Florida. He describes how popular ideas of how proteins get into the nucleus are inadequate. He suggests a more effective mechanism. Interview Transcript
- Interview with Mike Levin who is a geneticist at Tufts University. In his interview he describes the work he has done to map voltage gradients in cells. He uses electrical signals to suppress tumor proliferation. Interview Transcript
- Interview with Colin McCaig, Head of School of Medical Sciences, Institute of Medical Sciences,
University of Aberdeen, Scotland Interview Transcript
- Interview with John Marko, Professor of Molecular Biosciences, Physics & Astronomy, Northwestern University
He is also a team leader in the PSOC at Northwestern University. Interview Transcript
- Interview with Joel Kralj – who has made an amazing discovery: humble bacteria ‘blink’ electrically and you can watch a movie on his website showing them do it! It was previously thought that only cells in the heart and the nervous system behaved in this way – but that was because the voltage inside small cells was very hard to measure and biologists had no reason to suppose there was much electrical dynamics going on. But they were wrong – at least about bacteria – and Joel is now looking at different types of cells in humans to see if they too have an electrical life. It’s an open question and very intriguing.
Joel’s paper on the subject was published a few months ago in Science Magazine. Interview Transcript
- Interview with Jessica Cunningham who works at the Moffitt Cancer Center and Research Institute in Tampa, Florida Interview Transcript
- Nicole Moore of the National Cancer Institute summarizes the highlights of the meeting
Interview with Robert Gatenby
Robert Gatenby: I’m Bob Gatenby from the Moffitt Cancer Center in Tampa, Florida.
Pauline Davies: And Bob you were talking about ways that proteins get into the nucleus?
Robert Gatenby: Well the pathways are very important in cancer research because they take information that comes to the cell membrane that are like growth factors, these are instructions to grow, or to not grow or whatever it is that cells communicate with each other. These are then communicated to the receptors on the cell membrane, but they have to be acted upon in the nucleus, so the cell needs to carry that information from the cell membrane to the nucleus in a way that the nucleus could then deconvolve or kind of sift through that information and make an action. So if the cell needs to decide to proliferate, to kill itself, to move, all those sorts of things require information from its surrounding area. And so in cancers it turns out that this function in various path ways is extremely common, and so for example about sixty percent of cancers or so have a mutation in one of the components of the epidermal growth factor receptor pathway. And what happens is that that receptor or one of the components is basically always turned on, and so what happens is then the cell gets continuous growth signal indicating that it should be proliferating and of course that’s one of the things that contributes to the formation of cancer. And there is tremendous interest in finding small molecule drugs that will block those mutations and turn off that signal, and it turns out that when you do that, not only does the cell stop proliferating, but it often causes itself to die. So this is an effective therapy in cancers, although in most epithelial cancers it does not last very long, it happens that the cell becomes resistant. I’m interested in this because it’s just so common in the cancer world and when I look at it though it turns out at least to me that the conceptual models that exist of these pathways are very schematic. So these proteins have to move from the cell membrane to the nucleus, which is conventionally shown as a relatively short distance relative to the size of the proteins, but that’s not really at scale and it turns out if you draw this to scale it’s about a thousand protein diameters between the cell membrane and the nuclear membrane. So that’s not a distance that proteins can travel easily just by random walk or diffusion. And so this turns out to be a problem, a physical problem for movement of information that normal cells have to resolve and then when we think about blocking that pathway in cancer cells, we need to take into account how these proteins move from the cell membrane to the nuclear membrane, how they interact with each other, so you get cross-talk and probably within that are the mechanisms for resistance.
Pauline Davies: Yes I was struck by that because it seems in the models that people typically look at, it seemed very simple, and as you mentioned it was all just words, description of how the proteins got inside, but when you think about it in the terms of the distance they have to travel it’s a completely different way of thinking about things.
Robert Gatenby: Yes it tends to be something that cell biologists just have kind of ignored, and I don’t know why exactly but it’s a problem that I think we’ve not really been very aware of, and so it’s a lot easier to do the bio-chemical experiments, you can really sort of just seeing how these things interact with each other in a test tube and ignoring the physical reality of movement.
Pauline Davies: So I think that you mentioned that some favorite mechanisms would be diffusion or microtubules pulling these proteins in, but you think that that’s not adequate?
Robert Gatenby: Almost everybody when you ask them about this has an idea of how it might happen but those tend to be relatively ill though out. So the most common one is diffusion, that simply these proteins move by random walk or diffusion from the cell membrane to the nucleus. Again that would be fine if the distance was relatively small relative to the size of the protein, which is how these pathways are usually depicted in the textbooks. But a thousand protein diameters is a very long distance. Some people think they flow along microtubules and proteins that are recently synthesized can be delivered to locations by microtubules, but this would really require that they find there way into these tubules, the tubules aren’t usually that long and it really is a shuttling back and forth. And then the other thing that people talk about are microfilaments, and there’s this idea somehow they get grabbed, each protein gets grabbed by microfilament and pulled to the nucleus. Again when you start to sort that through and think well how practically can that happen, it doesn’t really make sense.
Pauline Davies: So what is your suggestion?
Robert Gatenby: well my thought is that there has to be some kind of internal structure that promotes movement, and I was struck by the fact that the ways that this information is passed from protein to protein in these pathways is through phosphorylation, when one protein then adds phosphate groups to amino acids in the next protein. And this is well known, this is kind of the coin of the realm for information transfer and all the focus so far has been on the fact that these phosphates change the configuration of the protein, but they do that by adding negative charge and so what interests me is that the protein itself becomes very negatively charged with this and maybe the cell uses that to cause movement. So we postulated the idea that if you had an intercellular electric field that would tend to move proteins from the cell membrane to the nuclear membrane if they were negatively charged, that you could provide a mechanism that would then allow them to move very quickly. So we started with this idea that there would be an electric field generated by the nuclear membrane or some place around the nuclear membrane that would draw these proteins toward the nucleus when they were phosphorylated. And so that was kind of our original idea and then as time went on we began to realize that there’s really more to that then just the phosphorylation piece because proteins have very specific and a wide range of what’s called the isoelectric point and what that means is that in the ph of the cell which is usually between 7.2 and 7.4, some proteins have a very high isoelectric point which means they are positively charged and others are very negative and what that means is that even under normal circumstances, the cell can use that to push the proteins in one direction or the other. For example, one protein that has a high isoelectric point will be positively charged throughout the cell and will then tend to be pushed by the electric field out toward the cell membrane, whereas something that is negatively charged would be located near the nuclear membrane. And so this actually provides the cells with an opportunity to really localize their proteins in very specific ways, and I so I think it adds another layer of organization to cells.
Pauline Davies: And would the cell mechanism of protein movement be a lot faster, doing this, than through the microtubules, or microfilaments, or diffusion?
Robert Gatenby: Yes we calculate that in fact a protein under these circumstances can move from the cell membrane to the nuclear membrane in less than one second, very, very fast movement. And more than that, it’ll even get funneled directly toward a pore in the nuclear membrane which is where it needs to go in order to get through to interact with the DNA.
Pauline Davies: Do you think you will ever convince the people who favor the other explanations? Because I presume they come from a different background.
Robert Gatenby: I think that as we’ve sort of learned here, in some ways it’s convincing the physical scientists about this and sort of working through how an electric field could be developed. As a non-physicist, I’m relying on working with bio-physics people to sort of think through this. What’s interesting is that the biologists, when I presented it to them, have almost slapped their hand on their forehead and say ‘you’re right, we don’t really know how this works.’ That has been, I would say in general, there’s been some skepticism, there’s always going to be skepticism, but there’s always been, I think, the recognition that this is addressing a real problem that’s been ignored. So whether it’s right or not, I think they reserve judgment but the facts that there needs to be some understanding of this, is sort or dawning on people now.
Pauline Davies: And how will this play into the cancer research field?
Robert Gatenby: well because these pathways are typically always on and so there’s a constant steady movement of these messenger proteins from the cell membrane to the nuclear membrane, the dynamics of this is very different in cancer. And we don’t know yet, we haven’t done measurements yet on whether the electric field is different and if it different, is it different because these proteins pathways are turned on or do these proteins pathways get turned on because the electric field is different? In other words you might say ‘if the cell is going to die if it doesn’t get, a constant stream of these messenger proteins stimulating the nucleus, which is the case, if you start to get this function of the underlying electric field so that the movement of the proteins is no longer very efficient, does the cell have an opportunity to respond by up-regulating the number of proteins that are being made and does that contribute to the process of carcinogenesis. That’s pure speculation of course but that’s one of the things that we’re thinking about. There is mitochondrial we know that this is energy requiring and there is the mitochondrial theory of aging which is that energy production by the mitochondria steadily declines as you get older, and so again you might say that this could be the result of senescence and then could be a factor at least in some cancers, but of course that’s pure speculation.
Pauline Davies: And how could this ever be used for maybe preventing cancer or controlling cancer?
Robert Gatenby: Well we have found that changing the extracellular pH does alter the pathways that develop cancer. We have an article being published in the article in the journal of urology in the next few months where we’ve shown that if you take TRAMP mice; TRAMP mice get prostate cancer, if you put them on a sodium bicarbonate diet at a young age they don’t get cancer at all. We know that by perturbing some of the physical properties of the cell and its surroundings, that we can alter the pathway to cancer. Now whether this will be part of that or not I don’t really know and that may really be too far-field to speculate, but…
Pauline Davies: This is fundamental science and we ought to about it anyhow.
Robert Gatenby: Well I just enjoy it, I hate to say it, but this is what twelve years of Catholic school will do to you. I had a little bit too much dogma from the school and so I generally get a kick out of sort of poking fun at dogma, and so in some ways I just enjoy doing it because I think that this is just an area that people take for granted and so I get a kick out of just, you know, poking my head into it and mixing it up a little bit. That’s really all I want to do.
Pauline Davies: Thank you very much.
Interview with Mike Levin
Mike Levin: I’m Mike Levin and I come from Tufts University.
Pauline Davies: Mike, how would you describe yourself?
Mike Levin: Well originally I was trained in computer science, I worked in artificial intelligence and artificial life and my interests were in modeling complex adaptive systems to understand how we could make robots and flexible systems that repair themselves and reproduce and so on. After that I got a PhD degree in genetics because I thought it was really important to understand how the living world solved these problems.
Pauline Davies: And you were giving a fascinating talk today about electrical fields in biology and you started off looking at salamanders?
Mike Levin: Yes, so the salamander is an excellent system because we have this complex vertebrate animal here that’s able to regenerate limbs, eyes and jaws and parts of its brain and restore them perfectly throughout adulthood, and of course this is the dream of biomedicine and so I think learning from these systems is absolutely key.
Pauline Davies: And even when you, I think you were growing a tumor on the leg and then cutting off the leg and then the tumor helped regenerate the leg, is that correct?
Mike Levin: So this is not our work, this is something that’s been done since the 40s and in fact has not been looked at since then and I think it’s a very profound result. What it shows is that the tumor actually becomes normalized as the limb regenerates. So the active patterning influence that the body exerts during regeneration is able to bring tumor cells under control and cause them to function as normal cells within the body plan. So I think that has real profound implications for the way we address and understand cancer.
Pauline Davies: You did a variety of experiments using electrical fields on single cells and tissue. Can you describe some of these for me please?
Mike Levin: So we actually do not use electric field application at all. What we’ve done is spend the last. We are working with voltage gradients that are endogenous, they are native to the cells; cells are generating these voltage gradients. We don’t want to apply any external electric fields. We’re interested in the patterns of difference of voltage gradients among different cells, and we’ve spent the last ten years developing molecular tools for functionally perturbing them. So we have ways of seeing these voltage maps in embryos and tumors in vivo and we have ways of modulating them quite specifically, so we’ve been able to show that when you change these voltage gradients you can make very targeted changes in pattern. So we can, for example, cause the regeneration of legs and tails, we can cause tail wounds to form a head in worms instead of forming the tail; we can induce cells in the body to become eyes, make full normally-patterned eyes. And so on, so a large scale of body structures are determined by the voltage gradients and we’ve developed tools to allow control of them.
Pauline Davies: I think you were saying that the voltage gradients come before any chemical signals are given off that can lead to these changes.
Mike Levin: Well in terms of normal events there’s a cycle where genetic information such as the expression of channels and pump genes are what causes these electrical gradients, but the electrical gradients then change gene expression so they change the position and the amount of these ion channels, and so it’s a big cycle so to speak, the one changes the other so you can’t really say which is primary, basically it’s a circle, they feed each other. But in terms of the tumor data we showed is that we can actually see, and this is still unpublished data, we’ve shown that we can actually detect cells that are going to make tumors before it becomes anatomically obvious that they’re going to do so.
Pauline Davies: And you were showing that you could in fact disrupt the tumors to actually turn them back to something else?
Mike Levin: What we’ve shown to date is that we can suppress the proliferation of tumors even though they’re still expressing the oncogene and we can show that in certain cases, cells that would have otherwise gone on to be tumors, we can cause them to become other structures. We still have a long way to go towards full normalization of an ongoing tumor; we have not shown that yet.
Pauline Davies: Another thing that you were doing that I think could be quite useful in cancer prevention is you were finding a way of visualizing tumors before they could be seen by normal methods.
Mike Levin: Exactly. Part of the changes that occur during tumor genesis when cells stop obeying the normal patterning cues of the body, you can see some of these changes by an abhorrent physiological signature. So one of the things were doing is using fluorescent dyes that report various electrical aspects of these cells to try and find a signature by which these cells can be none invasively visualized.
Pauline Davies: And what you were suggesting was that you would bathe the tumors and the cells around the tumors in some sort of dye that you would then be able to pick up using electrical signals.
Mike Levin: So the dye is florescent, you just pick it up with a camera. It floreces to different degrees depending on the voltage so the sort of dream technology here is that this is a diagnostic tool where you can bathe the skin or the oral mucoso or any other part of the body in these dyes and then you simply use a camera to pick up the… and you could also use it to visualize the tumor margins during surgery when the surgeon is trying to figure out how much to cut.
Pauline Davies: And this isn’t some far-flung dream, this is something that you can see now using cameras.
Mike Levin: Yes this works now in our frog system. The trick is to sort of move it towards a mammalian system that has real clinical relevance and we have the collaborators with whom we’d like to do that, but we have not done that yet.
Pauline Davies: And how much smaller can the tumors be that you can pick than they would be in normal visualization?
Mike Levin: In the frog we can do this long before any would be picked up by normal visualization systems, how it’s going to play out in a clinically relevant model, we don’t know yet. We just don’t know.
Pauline Davies: You were also looking at flatworms and doing amazing experiments with flatworms, tell me about those. I know you had some with four heads.
Mike Levin: Yeah the remarkable thing about flatworms is that they can regenerate after any type of injuries so no matter what body part you cut off, they will regenerate a perfect replica. And so that is a great model system in which to understand where that patterning information is stored and how we can learn to control that. Because learning to control dynamic growth is the key to preventing and fixing cancer, I think. So what we’ve shown is that unnatural patterns in bioelectric gradients are very important in the planarium flatworm to be able to know what structure it should form in any given wound. So by manipulating or taking advantage of these gradients and changing them, we can trick the worm into building different structures at the wound. So we can make two-headed worms, four-headed worms and so on.
Pauline Davies: And that was another very impressive aspect of your work, you can be specific about how you makes these alterations, can’t you?
Mike Levin: Yeah the key is that we’ve spent a lot of time developing new tools and reagents, protocols and genetic and pharmalogical tools with which we can be quite specific about what membrane voltage level we achieve and this is part of mapping out what we call the bioelectric code. We really need to understand how the different voltage patterns determine different structures and we’re just beginning. The field is in a very early stage, we’re just beginning to do that.
Pauline Davies: Do you think that your work and similar work will have a profound impact on how we view development and also the implications for cancer?
Mike Levin: Well I think development, regeneration and cancer are all sides of one coin. I think a true understanding of development would have transformative implications for cancer. As for my work, I certainly hope it will but you know we all hope that I suppose.
Pauline Davies: Great. And one other thing from the start of your talk you said that animals that regenerate don’t tend to get cancer, is that correct?
Mike Levin: This is true. When people talk about why it is that humans have such reduced regenerative potential relative to other species, the answer that most people are now told is well that’s because if you’re a body plan that has access to large number of rapidly proliferating cells, then you would be prone to cancer. There would be an oncogenic cost associated with the ability to regenerate, and this in fact is completely wrong in the sense that animals that have high regenerative ability are in fact animals with the lowest incidence of cancer and so it’s quite clear that the ability of the body plan to exert strong patterning control over new growth is what’s important for regeneration but also for suppressing tumor formation.
Pauline Davies: And the very final point just to get this completely clear, we should be able to use electrical signals to either promote or to suppress cancer.
Mike Levin: That’s correct. Because electrical signals, and I don’t necessarily mean applied electric fields, I mean patterns of voltage gradients within the tissue, are an important component of what cells know to do. So by tweaking those signals we should either help cells to go along with the patterning program of the host and make normal tissue or conversely to abandon that plan and form tumors.
Pauline Davies: Thank you so much.
Interview with Colin McCaig
Colin McCaig: My name is Colin McCaig, I’m interested in directional cell migration in the context of wound healing and developmental biology I guess as well. I’m particularly interested in small electrical signals that are naturally generated and exist in an extracellular species and they play pretty profound roles in directing a whole bunch of different cell behaviors which range from directed cell migration, directed cell division, control of the cell cycle and differentiation of cells as well.
Pauline Davies: And what were you telling us in your lecture? What was your story?
Colin McCaig: I guess the take home message was that there are naturally occurring electrical signals that developmentally are use by tissues to create their natural networks of interactions between each other. You can mimic those signals and then use applied signals in regenerative context, people have done that to look at the nervous system, and to look at spinal cord regeneration for instance. They’ve also done it in the periphery to look at wound healing and there are medical devices using those kinds of technology to enhance wound healing.
Pauline Davies: In fact you were the person who was showing how if you change the electrical stimulation you can get the cells growing towards a a wound to actually reverse.
Colin McCaig: That’s right. So we’ve known that for some time and I guess it’s instructive in the sense that most people have been interested in small chemical gradients of molecules within an extracellular species that cells can read and respond to, and we’ve been able to show that electrical signals are every bit as potent and you can kind of play games putting them one against the other and see what the hierarchy of signals are that cells are capable of reading and responding to a wide variety of extracellular guidance cues and if you can get the conditions right you can certainly override a lot of the chemical gradient information with these kind of electrical signals as well.
Pauline Davies: And what relationship does all this have to cancer?
Colin McCaig: That’s a trickier question. There is a sporadic literature that would suggest that there are similar electrical signals between cancer tissue and normal tissue. It’s also the case that where metastasis takes place for instance in breast cancer the cancer cells break across the epithelium and in a sense create a localized wound with its own electrical signals and the directionality that the migrating cells head off in to initiate metastasis is the same directionality that they would have when you expose them to an applied electric field and they show directed migration. So it might be possible to use these kinds of electrical signals to slow down or reverse might be a little ambitious, I’m not terribly sure whether it would help you to reverse the migration of a metastasizing cells because they’re going to have to go somewhere else. There is another aspect to it which nobody has talked about and I didn’t get on to talking about today, which is about controlling the endothelial cells and controlling vascularization so we can also use these electrical signals to direct and migrate blood vessel orientation. So in terms of the development of tumors and their requirement for angiogenesis and to initiate their own angiogenic responses there might be a twofold manner in which electrical signals could influence tumorgenesis. One would be to limit angiogenesis into the tumor and the second would be to potentially prevent the directed migration of metastasizing tumor cells.
Pauline Davies: And you said to me well where would these migrating tumor cells go, well it would be great if they could go back into the tumor that they came from.
Colin McCaig: If you could keep them in one place that would be an advantage over them going all over the body, absolutely. So yes there is the potential for doing that, for retaining solid tumor and preventing metastisization and I guess that would be surgically much easier to then remove that tissue.
Pauline Davies: So you’ve come all the way from Scotland for this meeting, has it been worthwhile?
Colin McCaig: Yes it has, it’s been great. It has actually been a very exciting meeting. It’s such a pleasure being in amongst a group of such disparate-minded people. The kinds of talks I normally give are often to cell biologists or physiologists and not so often to physicists so the range and left-field nature of the questioning is really exciting and keeps us on our toes I guess, but it’s been good.
Pauline Davies: Do you think this meeting could have any influence on the work you might do in the future?
Colin McCaig: Yeah almost certainly. There are people here that I will interact with in the future. I’ve talked to a guy who is coming over to Scotland and we’ll invite him up for a seminar anyway. So yeah I think there will be lasting collaborations from us.
Pauline Davies: Great, thank you very much.
Interview with John Marko
John Marko: I’m John Marko, I am a professor of physics and astronomy and molecular biosciences at Northwestern University and I work on trying to understand how the machinery inside cells works, mostly how DNA is processed and packaged inside the cell.
Pauline Davies: One of the things I remember from your talk is that you stretch DNA, didn’t you, just using electrical potentials?
John Marko: Well we don’t use electrical potentials, we use magnetic fields on small particles which are magnetic which we can attach to the end of DNA molecules, and that type of technique is often called a magnetic tweezers experiment. And you know, most proteins that do something to the DNA, that bind the DNA and package DNA or maybe cut one of the strands of the double helix or both of the strand of the double helix or otherwise just land on DNA to control gene expression, they’re generally changing something about the mechanical properties of DNA and so we can detect those events and in many cases analyze them in a very precise way using a mechanical experiment where we pull on and twist along a DNA molecule and watch what happens as proteins process it. So it’s kind of one of the typical experiments we carry out in our lab.
Pauline Davies: So when you do this, what do you see that is significant?
John Marko: Well for example one of the experiments we’ve been working on recently has been looking at recombination of DNA sequences, how two specific DNA sequences can be joined together and then the DNA molecules can be cut and pasted to make new DNA molecules at that point. That happens a lot in prokaryote cells, it happens in the immune system as well as type of process to shuffle the antibody genes in our immune system. So we’ve been studying a particular type of site specific recombination which had been somewhat mysterious as to exactly how it takes place and it turns out that we could establish that there’s a rotation that takes place in the enzyme DNA complex that does this that we could directly see in a micro-manipulation experiment. So that type of experiment is very complimentary to the kinds of experiments that a usual biochemistry lab would do, and so we can answer questions that would be very difficult to answer by conventional biochemical methods. We’re also working quite a lot on the enzymes that disentangle DNA. DNA molecules are huge and get tangled inside the cell and need to be disentangled by specialized enzymes that cut DNA and pass DNA through itself and so these types of single molecule experiments are very good for analyzing those kinds of enzymes where we can just directly watch the passage of one DNA molecule through another DNA molecule.
Pauline Davies: Well I guess if you can manipulate DNA by magnetism and it’s coupled of course with electricity, there must be lots of electrical things happening inside cells. Is that correct?
John Marko: Well you know DNA is very heavily electrically charged as a molecule inside cells, conditions you find inside a cell. The DNA molecules are heavily negatively charged, well what the means is that the proteins which bind to DNA are typically positively charged and that kind of static electrical interaction between molecules plays a big role in all aspects of protein and DNA interactions. So we use that, we have to deal with that, it’s a problem in some experiments and it’s a feature in some experiments, and we’re often using and exploiting the electric nature of protein-DNA interactions to control how strong protein-DNA interactions are. So that’s an important tool for all of our experiments. And certainly in the cell, modulation of charge on molecules is one of the fundamental ways that molecule-molecule interactions are controlled and many DNA-binding proteins have their charges modified to regulate them, and that changes how a given protein may interact with DNA. In fact in our lab we study instances of that, how phosphorylation or dephosphorylation of specific proteins can change their interaction with DNA essentially by changing the electrical charge of a region around the molecule. So definitely electric forces play a huge role in essentially all DNA-protein interactions, and many other processes inside the cell as well.
Pauline Davies: Do you think enough attention is given to this area?
John Marko: Well, this meeting has addressed many different types of electrical phenomenon involving cells. So in my case I’m worried mostly about what you might describe as static electric phenomena, actually statistical mechanical equilibrium electric phenomena, which control interactions between molecules at the nanometer scale, but one of the interesting things we’ve seen in this meeting has been a lot of reports of how electric fields in cells and around cells can affect cell behavior. For me, from my point of view, those are very interesting experiments, but then I want to know what molecules are involved in sensing those electric fields, presumably through sensing of eclectic currents, because electric fields in the cell will always drive electric currents. And for me it’s that big question of how molecules on the cell surface and inside the cell detect and then generate chemical signals inside the cell to process electrical information coming into the cell. And it seems to me that a lot of that is not very well understood at the molecular level how sensing of electric fields is going on is not very well understood. To me that would be on of the first questions I would start to ask when I worry about electric phenomena in cells at large scales; how’s that type of electric field information processed, detected and processed by a cell and then go on to worry about how that information processing in the cell affects cell behavior and organization of tissue in multicellular organisms and so on. We’ve heard a lot of cell biological and organismal talks at this meeting.
Pauline Davies: Have you enjoyed the meeting?
John Marko: Oh yeah, it’s a great meeting. I’ve really enjoyed the meeting and I’ve learned a fantastic amount and I’ve had a lot of good ideas for experiments based on various aspects of things people have talked about and the level of research percentage that has been uniformly very high.
Pauline Davies: What is the most surprising thing about your own research that you can tell me right now easily?
John Marko: Well probably the most surprising thing about my own research is how we can start to understand how microscopic events, interaction between molecules, can be coupled to large scale changes in cell behavior. And also how unexpectedly molecules even at the nanometer scale can quickly cease to be described by simple, equilibrium statistical mechanics that all of us physics people would like to use to describe nanometer scale behavior, and it’s always amazing how few atoms you need to start to have glassy behavior where you have a molecule that is suddenly able to have memory of where it’s been and what it’s seen. And this can happen easily at the single protein scale and it’s always kind of frightening to see that kind of thing, beyond even surprising, kind of frightening to see, information stored on molecules and a molecule’s history, encoded onto its structure even at the sort of single molecule level. So that’s one of the most surprising things of the experiments we’ve done.
Interview with Joel Kralj
Joel Kralj:My name is Joel Kralj and I’m a postdoctoral researcher in the chemistry department at Harvard University.
Pauline Davies: And you were walking about the electrical properties of cells and had some really wonderful examples. And the E-coli is stuck in my mind, tell me more about that.
Joel Kralj:Yeah, so it’s kind of a shock. We developed a new sensor to measure voltage inside of cells, and we found that, quite by accident, when we looked at E-coli expressing this voltage sensor that they showed transient bursts of fluorescence indicating that they had electrical depolarizations which was something that nobody had ever seen before.
Pauline Davies: I think we better back-track a little, because what were E-coli doing fluorescing?
Joel Kralj:So the tool that we developed is a protein that will change its fluorescence depending on the voltage and the specific protein we use is the microbial rhodopsin. So the rhodopsin will change its photo-physical properties depending on the amount of voltage across the cells. So by looking at amount of fluorescence we will have a read out of what the voltage is inside the cell. So we added our voltage-sensing protein, to the E-coli, so we were actually looking at the voltage inside of the cell. And so when we imaged the voltage we found again the transient bursts of fluorescence that we correlated with depolarization much like an action potential in a human neuron.
Pauline Davies: And his electrical potential seemed to move right through the cell?
Joel Kralj:That’s correct. As far as we could tell the entire cell was going up and down simultaneously.
Pauline Davies: Now was that a tremendous surprise?
Joel Kralj:It was actually an incredible surprise and because it was so shocking it took us a long time to actually verify that these findings were correct and it’s still a big surprise in the community we think.
Pauline Davies: Because of course we’d expect to see some electrical things going on in cells, but just to have something encompass the whole cells, is that the surprising thing?
Joel Kralj:Well that’s definitely part of it but for a long time spontaneous electrodynamics were thought to be the realms strictly of neurons and cardiomyocytes,, things relegated to higher mammals like humans, monkey and rats. But to find that bacteria were capable and actually undergoing these exact same electrical transitions came as a complete shock and actually makes us think that evolution has favored some of these electrical transitions very early on, much earlier than was previously thought.
Pauline Davies: So are these electrical transitions the same in every cell that you’ve studied?
Joel Kralj:So far we’ve seen them in two different types of bacteria but there are millions of species, so right now we’ve looked into and have seen electrical depolarization in two.
Pauline Davies: And how do you introduce this to the cells?
Joel Kralj:So with bacteria we can give them DNA they will recognize and express the proteins. So we trick them into expressing our protein of interest. With mammalian cells we actually encode the DNA into a virus which then infects the cells and then tricks those mammalian cells into expressing our protein. So we use the endogenous cellular machinery to make our protein, but we either use viral or DNA-based methods to get these cells to express it.
Pauline Davies: And in the mammalian cells, as you mentioned, you’d expect to see electrical potentials associated with neurons, but do you see it throughout the cell as well?
Joel Kralj:Yeah, so when you look at a neuron, they undergo well-defined action potentials that have been seen for sixty years. So we can actually record the entire cells undergoing one of these too except we do it via imaging so we can make movies of the neuron undergoing these action potentials in exactly the same way we that make movies of the bacteria that are flashing.
Pauline Davies: And what about cells that aren’t neurons?
Joel Kralj:So we haven’t looked, and I think that voltage has been largely underestimated in all different sorts of cell types, but there hasn’t been a particularly good an easy way to look. So one of the future goals of this project is to start looking in a broad variety of cells and to see is voltage a component of their normal lifestyle, then to see how they’re regulating voltage in response to different perturbations.
Pauline Davies: Yeah because from what you’ve been saying, these transitions, these electrical processes are happening in bacteria, why wouldn’t they be happening in ordinary cells in our bodies, not just the neurons.
Joel Kralj:Exactly. So I think it’s quite interesting in terms of the way life developed, that bacteria are capable of these electrical depolarizations.
Pauline Davies: And what does it say about what’s going on in our cells for instance?
Joel Kralj:Well I think what it suggests is that there’s an evolutionary connection between the bacteria undergoing these depolarizations and the origin of the really complex neural processing that goes on inside our brains and the cardiac action potential that drives the beating of our heart.
So in terms of wound healing that we’ve heard about earlier and immune response in terms of insulin release from beta cells, these are all processes that are thought to have electrical dynamics but it’s just been very difficult to study because of technical reason that I think now we have a tool that will allow us to look at them in greater detail.
Pauline Davies: The rhodopsin that you mentioned, that’s what gives bacteria in those ponds outside of Los Angeles the color.
Joel Kralj:Yeah that’s right. It’s a great example in science of how some completely random discoveries, like random bacteria in a salt pond can give rise to this incredibly powerful tool, and I think it really speaks to funding basic science because this random protein found in nature can confer these amazing abilities for us to look at different types of cells. So it’s really kind of exciting that we were able to re-purpose this protein into this sensor.
Pauline Davies: And what connection does all this have to do with cancer?
Joel Kralj:So I think that remains to be largely explored. One of the big overriding topics of this seminar is to look at the role of voltage in cancer. I’m hoping that with our tool we can now address in much finer detail how these cancer cells are changing their voltages with respect to healthy cells and then can we use that knowledge to in some way revert the voltage state back to a healthy cell.
Pauline Davies: What have you gotten out of this meeting so far?
Joel Kralj:I think what I’ve gotten out of this meeting is just a greater appreciation for the role of voltage in biology. So both in terms of cancer and its effects and also in terms of development, so how voltage regulated everything from us developing in the embryo to frogs and how we can hopefully turn voltage into a tool to cure or process some of these diseases.
Pauline Davies: I think you’re probably in the right field at the right time.
Joel Kralj:Yeah, well that’s the hope. Thank you.
Science 15 July 2011:
Vol. 333 no. 6040 pp. 345-348
To watch the movie, go to :
Interview with Jessica Cunningham
Jessica Cunningham: I’m Jessica Cunningham and I’m from the Moffitt cancer research center in Tampa, Florida.
Pauline Davies: so you’ve been attending this meeting for the last couple of days What’s your impression of the meeting?
Jessica Cunningham: I really like the basis of the meeting that we’re not just presenting known data, we’re actually trying to talk about what we don’t know and I think that is the most important part. We can talk about what we do know all day and it doesn’t get us anywhere. So it’s nice to talk about people who are trying to push the envelope.
Pauline Davies: Is there anything particularly surprising that comes to mind when you were in the meeting?
Jessica Cunningham: So I really liked the talk about regeneration and how the electrical components of a cell have to really dictate how regeneration occurs and the movies of actually seeing electrical potential waves changing within embryogenesis of splitting cells and that it could actually dictate genetics instead of the other way around. It’s really mind blowing. It’s really interesting.
Pauline Davies: And what about cancer? Anything that directly relates to cancer?
Jessica Cunningham: So there’s some evidence that these membrane potentials actually break down in cancer cells and that maybe intercellular electrical fields also break down in cancer cells and if these are highly regulatory systems, if these are big proponents of who am I and what am I doing as a cell and they break down, it’s not hard to think how that would directly translate to cancer.
Pauline Davies: And you showed some movies yourself. So tell me about your own work.
Jessica Cunningham: So we actually study the consequences of an intracellular electric field, so not a membrane potential per say, but actually what would happen if an electric field could actually be within the cytoplasm and how this pertains to pathways, so messenger proteins and the like. So it’s interesting to talk about the difference between a diffusive process and then something that is highly directed by electrical fields. And it actually adds this whole level of information that you can get. In cells with diffusion you don’t get when or where a signal s coning from but if there were some organizational principles within the cell you can actually get when and where signals are coming from and this could be a very big change in how information pathways are discussed in normal cells and cancer cells.
Pauline Davies: I seemed to remember that you had a schematic of the cell where you had looking down almost as a column into the nucleus and you had some proteins that were going part of the way down this column to the nucleus, bumping into others, transferring information, and there were about three different types of proteins going on and none of them actually went all the way down to the bottom, they just passed on the information to other proteins, is that right?
Jessica Cunningham: Yeah, so many protein pathways have more than one protein and the one that we map has four so one is bound to the cell wall and then there’s three within the cytoplasm and only one of those actually goes into the nucleus. So the other two are bouncing back and forth, passing this message between these other proteins but it’s only the one last protein that actually goes down into the nucleus.
Pauline Davies: And yet there are electrical messages being passed?
Jessica Cunningham: Yeah so protein pathways, everyone agrees that how these pathways are, quote on quote, activated is adding what is phosphate, and a phosphate adds two negative charges, and the negative charges are not really discussed in big consequences, they talk about conformal changes of the proteins themselves, but allowing these negative charges to be part of a much bigger organizational principle of the cell could be ground breaking or it could be all awash, I don’t know yet.
Pauline Davies: And what implications does that have for cancer in particular?
Jessica Cunningham: So, you know, it’s very hard to talk about a cancer cell and how is a cancer cell broken when we may not even know how normal cells work correctly in the first place. So I think we’re kind of jumping the gun a little bit trying to say what is wrong with a cancer cells when we have a very hard time defining what is right in normal cells. If we can’t talk about how normal cells keep themselves, quote on quote, ‘normal,’ it’s very hard to try and fix that if we don’t know what fixed mean. So we’re studying a lot of just normal pathways in normal cells and if we can figure out a better physical mechanism of how that really works we might actually have some ground to stand on to talk about what’s wrong with cancer cells.
Pauline Davies: So what was coming out to me during this conference was that we need to do much more fundamental research looking at the electrical properties of cells.
Jessica Cunningham: Yeah, so this is an area of biology that has kind of been ignored, it comes off as a little hocus pocus and I think it got ruined with electro-therapy where they were shocking people. It’s a little scary to think about our bodies as electrical systems and I also think it was also prohibited by the technology we had. So not until recently have we been able to measure these tiny electrical properties of a cell and I think as the technology gets better and also we get more comfortable thinking about that there is an electrical property of a cell again, that will start to be able to open up this whole area of science that has kind of been ignored a little bit, which is a shame.
Pauline Davies: Thank you. Fascinating.
Jessica Cunningham: Thanks very much.