Albert Lasker
Basic Medical Research Award

An Interview with Clay Armstrong
Interview by Denis Baylor

Denis Baylor, Professor, Department of Neurobiology, Stanford University, interviews Clay Armstrong, who shares the 1999 Albert Lasker Basic Medical Research Award with Bertil Hille and Roderick MacKinnon, November 1999. Dr. Armstrong is a professor of physiology at the University of Pennsylvania in Philadelphia.

Part 1: Ion Channels in Medicine and Biology
"I think that ion channels are the most important single class of proteins that exist in the human body or any body for that matter," Dr. Armstrong tells a hypothetical skeptic from medical school.

Baylor: So, Clay, it's really good to talk to you today.

Armstrong: Well, thank you, Denis, it's mutual.

Baylor: Well, I have a tentative plan for this interview, so I'll tell you in an outline what the tentative plan is. We can follow it more or less closely, depending on how it evolves. I wanted to ask you a little bit about how you see the place of ion channels in biology and medicine and then ask you a little bit about your family background and your family today. Then talk a little bit about your education and training in science—mainly the places and the people. And then really get into the meat of the science after that and talk about how you came to your wonderful insights into channel structure and function. And then talk a bit about what you're up to currently. And then the future. And then what you see the future of ion channel work being and what advice you might have for young people that are considering a career in science. Would that be reasonable?

Armstrong: Okay. Yes. That sounds fine.

Baylor: That's some outline of what we might do.

Armstrong: Wonderful.

Baylor: So, about the place of ion channels in biology and medicine. Suppose that a skeptical medical student came up to you and said, "Okay Dr. Armstrong I have too much to do. Why should I care about ion channels?" What would you say? (Laughter.)

Armstrong: Well, I'm confronted with that situation quite frequently. I'll be aggressive about it—I think that ion channels are the most important single class of proteins that exist in the human body or any body for that matter. And of course, the question is something like saying, "Which is the most important part of a car, the tires or the carburator?" You can't do without either. But all of the higher functions, all of the communication between the parts of the body, depend very crucially on the function of ion channels, and every perception, for example, is encoded in electrical form through the function of ion channels. Of course in your wonderful work on the retina and on the visual receptors, that's certainly the case that the ion channels are involved in the initial transduction of light into electrical impulses, which are then dealt with by the brain. The heartbeat is another example. It is an electrical timing system dependent on ion channels that produces a heartbeat. All of our thoughts, all of our motions involve the action of millions of ion channels—billions. Endocrine secretion. All of these are, of course, are in addition to the more basic functions of ion channels, which are involved in the very life of the cell—of every cell. No cell could exist without ion channels. So I regard it as extremely important and also medically important.

Baylor: Definitely. And it seems that these ion channels now have an increasing significance in medicine, because a lot of neurological diseases turn out to involve mutations in ion channels, don't they?

Armstrong: Yes, yes indeed. Well, epilepsy, for example, is one clear case. Myasthenia gravis is another. Various of the paralyses and myotonias. And that's leaving out, of course, the big one—which is not neurologically related—but the function of the heart, which is certainly one of the most important medical problems to be encountered.

Baylor: Definitely. And so the channels also, I guess, are going to be very important, increasingly important drug targets for medical therapies of one kind and another.

Armstrong: Yes, well that certainly seems clear, Tranquilizers, of course, are one of the more (important categories)—I think no one really knows. With some of the tranquilizers it's clear what the function is, but looking through the Merck index there are, oh, thousands of compounds that have been discovered empirically that do not have clear functions. And I would suppose that very large numbers of those must modify the action of ion channels in one way or another. Potassium channels are becoming clear targets of therapeutic intervention in, for example, diabetes and also in problems of arrhythmias of the heart. And again, going through the list of things that we don't understand. Thought, for example. Well, nobody knows in any precise detail how thought occurs, but that thought involves the use of ion channels seems very clear since all communication between cells and all communication within cells depends on ion channels. Well, it's just beginning. The only reason that the medical student could possibly think that it is not important is that we don't know enough yet.

Baylor: Yes.

Armstrong: And also I think that it is not a very popular subject. So generations of preceding medical students have told the hypothetical students that I've just encountered (in your question) that you don't really need to know that because it—in a sense it's perfectly reasonable—there's not enough that you can do about it at present. But that's definitely not the case in the heart or in the case of diabetes.

Baylor: And it really seems a certainty that down the road these ion channels will be essential—that medical students must know them cold in order to be good physicians.

Armstrong: Well yes, and to be medical scientists. The medical schools are supposed to be training medical scientists who will take things forward. So (for) all of those students who are hoping to shape the future of medicine, I think this is definitely a place where one should look. The problem generally speaking is that medical students, I think, have very good minds. They have retentive minds, but they tend to be somewhat less analytical than the students who go into physics and other pursuits like that. So they are not at present well trained in some of the things that one needs to know in order to get over the hurdle of understanding ion channels.

Baylor: I agree. Well, I think that's a pretty convincing answer. If the student doesn't believe you now, then maybe he shouldn't be in medical school.

Armstrong: Well, I would get read off of the faculty here if I said that too loudly, but I think one has to convince (not coerce).

Part 2: Family Background and Leisure Pursuits
Armstrong talks about his parents, his brother, his wife (who is also a scientist), their four children and his interests in marathons and mountain climbing.

Baylor: So Clay, could I ask you a little bit about your family background? Where you grew up and your folks and brothers and sisters and stuff like that?

Armstrong: Oh sure. Well, I came from the Armstrongs and the Margraves, and the Armstrongs and the Margraves converged on North Texas after the Civil War. And then both families, my maternal family, the Margraves, and the Armstrongs moved to Southeast Oklahoma. And oddly enough, it's a corner of the world that I thought no one would ever know about, and I discovered that, in fact, Chris Miller had family connections in Hugo, Oklahoma, which is where my maternal grandparents grew up.

Baylor: I didn't know that.

Armstrong: Yes. That was very interesting to hear about. But in any case, the Margraves, my grandfather and grandmother, had four daughters who were all lovely, interesting and intelligent. My father was the only surviving child of the Armstrongs, although my grandfather had 12 brothers, so that was a very large family. My grandmother (Armstrong) died at a relatively young age, so they had only two children, one of whom did not survive. My father went off to join the Army during the First World War and never finished college. I was born in Chicago, where he was working in a bank until the Depression really hit strongly, and then we moved back to, first Oklahoma and then finally to Dallas, Texas, where he worked in the Federal Reserve Bank. My maternal grandparents continued to live in Hugo, Oklahoma, and my paternal grandfather was a lawyer in a little town called Idabel, which was about 40 miles away. Well, it was an interesting place to visit, both of them—the cotton gins and so on. I have one brother and many, many cousins. It was always a very strong family because of the ties among the Margrave girls, who were really, really entertaining. My brother, in fact, lives in California, not too far from you. He lives in San Jose, and is a very entertaining and intelligent person, always interesting to talk to on virtually any subject.

Baylor: But you were the first one from your family then to go into medicine and science.

Armstrong: Yes. Of the two of us, Bob was more interested in history and English literature, and I went into medicine.

Baylor: And your family today is pretty interesting. I know your wife, Clara, is a distinguished scientist in her own right.

Armstrong: Yes, yes, well Clara is certainly more famous, deservedly, than I am.

Baylor: And do you two talk science? Do you talk to her about the structure of the release apparatus in muscle fibers, and does she talk to you about how channels work?

Armstrong: Yes! We talk to each other quite a bit. It's usually not so much about specific questions of our own work, but just general knowledge about cell biology and things of that sort. I learned a very great deal from Clara, including a positive attitude that, uh—I tend to be somewhat skeptical. Clara, on the other hand, is always enthusiastic about new work. And so her lessons to me in that regard have been very helpful, because I think in general that one learns much faster if you accept a new proposal and then have a very enthusiastic attitude toward it, and then later perhaps you can become more critical about it. But the general initial acceptance I think is an important step in learning about it.

Baylor: Interesting, although the scepticism's not all bad either.

Armstrong: No, no, but I think that should come a little bit later, after you have some grist for the mill.

Baylor: And you have several kids, right?

Armstrong: We have four children, John, a son, and three daughters. John works for Compaq computer. Katie is married and living in Palo Alto, as a matter of fact, and she teaches school and her husband is there at Stanford--Will (Talbot). Sandra plays the viola and is actually a professional, managing to make a living in what must be the hardest occupation of virtually any, because the competition is fierce.

Baylor: Definitely. That is very impressive.

Armstrong: But they actually heard a piece of very good news. They've been selected to play a new contemporary piece and will be paired on a CD with the Juillard Quartet. So that's spectacular.

Baylor: Wonderful.

Armstrong: I'm extremely pleased to hear that.

Baylor: Congratulations. That is wonderful.

Armstrong: And Cecilia is—well, as you know, since she's working with one of your colleagues—is a postdoc at the University of Washington with Fred, and well she's a delight, as they all are.

Baylor: She's really going to enjoy working with Fred Rieke. He's just a terrific young scientist. And I know that you like to run in your spare time. You've been doing this for many, many years.

Armstrong: I guess it's not quite correct to say that I like to run, but I do run, yes. I enjoy it part of the time. Running competitively is actually kind of fun, so I have even won a few races—in my age group.

Baylor: Wonderful. Have you done a marathon?

Armstrong: Oh, yeah. I have done six or eight marathons. I won my age group once upon a time in the Philadelphia marathon, so that was nice.

Baylor: Fantastic. You also do some mountain climbing with Clara I hear.

Armstrong: Oh yes, yes. Clara has turned out to be a very good mountain climber, so we had a wonderful trip to Nepal this spring, as a matter of fact. And we were walking around at very high altitudes for, oh, three weeks, I guess, in a place called Inner Dolpo, which was extremely remote. A very, very fascinating and trying trip. Both of us absolutely love that and would love to be back there even now. That's our second trip to Nepal. We had one preceding trip in which we went to the Everest region and got up quite close to the foot of Everest.

Baylor: That must be an amazing sight.

Armstrong: Oh, it is spectacularly beautiful. I love the Sierras, where we've also walked with great fondness, but the angle of vision involved in taking in these mountains in Nepal and particularly in the Everest region is, well, one certainly has to crane one's neck to see the tops of things. It's just astounding to see how tall they are and how beautiful. Every corner has a new vista that is amazing to see.

Part 3: Education and Training
A graduate of Rice Institute in Dallas, Armstrong went to medical school at Washington University, where he first became interested in electrophysiology.

Baylor: Clay, could I ask you a little bit about your education and training in science? Mainly the places and people for the time being, and then we'll get to the nitty gritty of TEA and such in just a little bit. But could you tell me just a little bit about your educational odyssey?

Armstrong: Okay. Well, life is a matter of chance. It didn't start off that way, but there were many points where chance was a big factor. I went to Sunset High School in Dallas, Texas, and worked reasonably hard as a student. So I managed to get accepted to Rice Institute, which was certainly the best school, I would say still is the best school in Texas. I went there for my undergraduate degree, and I was very fond of the place—still am. It was very rigorous in those days and not, I think, quite as accommodating to the students as it has become since. I think a third of our freshman class didn't return for the second year either because they hadn't made it academically or just didn't want to (return). But the education there was absolutely first rate. The teachers, the professors were all in love with their subject. And they managed to communicate that very effectively. So, I took a course that was relatively heavy in science and then proceeded to Washington University, which is and was a most excellent medical school. And I guess I had certain adjustments on leaving the ideal world of chemistry, physics, and coming to the much more empirical world involved in medicine.

Baylor: It is a different way of thinking, isn't it?

Armstrong: It certainly is—and necessarily. I mean, one can't be too theoretical about medicine, because it's an empirical subject largely. So anyway, that was an emotional shock. And with any emotional shock, as I'm sure you've experienced, you feel that it's improper, that you've learned the right things already, and anything that goes counter to either the feeling or the substance of what you already know must be improper. So certainly I had all of that feeling in trying to cope with medicine. But the first year, I was very fond of it. I liked biochemistry, even anatomy I liked a lot. But then in subsequent years when it came to pathology—for one thing I was color blind, so I couldn't tell the pink from the green tissues. But it was there in Washington University that I first got interested in electrophysiology.

Baylor: Oh yes, that was the place of Gasser and Erlanger.

Armstrong: Yes, right. And George Bishop was one of their people (colleagues). Very strong minded, very intelligent, wonderful man, who was the electrophysiologist-in-residence of the Neurology Department at Washington University, and it was in his general environs that I was working as an electrophysiologist. In fact, I was in the screened room right next to his office and using equipment that he had designed for measuring brain waves. And that was quite a fascinating learning experience. I actually learned some things about the brain and the evoked potentials in the visual system that I think still would be worth investigating.

Baylor: So this was work on the connections between the lateral geniculate and the visual areas 17, 18 and 19?

Armstrong: Yes. Yes. I was there working in the era, at roughly the same time as Hubel and Wiesel were doing their wonderful work on the connections of, well, basically the wiring of the visual system and the various types of receptive fields in areas 17, 18 and 19, and then the lateral geniculate. Well, one of the questions (facts) that came out, that was kind of obvious from, not just my work, but from the preceding work that George Bishop had done in analyzing the evoked potentials in the same areas, was that there are direct connections from the lateral geniculate body to areas 18 and 19. And Hubel and Wiesel, I think, at least initially tended to think more in terms of serial projection from lateral geniculate to area 17 and then from 17 to 18 and so forth.

Baylor: That's right. Certainly that was one of the big points or fairly big points of their work.

Armstrong: I think it is now clearly recognized by everyone that, in fact, there are direct projections from the lateral geniculate to some of the higher numbered areas. My favorite from the point of view of getting attractive looking evoked potentials was area 18. And there one could analyze the extra cellular field potentials and discover a synaptic potential in layer 3(b). One could see, in my analysis, firing of the initial segment of the axons projecting downward from the layer 3(b), firing of the cell body, and then activity that had to be in the apical dendrites of the pyramidal cells in that region. And then there was a quite fascinating story to my mind about inhibition. If you preceded a strong stimulus with a very small stimulus through the same electrodes so that this was all firing one family of axons projecting from the lateral geniculate to area 18, you could completely suppress the post synaptic activity in the layer 3(b) pyramids with this small preceding shock. And you had to allow an interval that was sufficient for transmission through one extra synapse. So it all fitted with the idea that this one family of axons had two connections. Direct connections that were excitatory to the layer 3(b) pyramids But the same family (of cells) then received inhibitory input such that one could imagine that those same axons coming from the geniculate synapsed with inhibitory cells (which) then inhibited the layer 3(b) pyramids. That was in general quite consistent with the picture of Hubel and Wiesel. One could easily synchronize this, harmonize this with their story on the inhibitory surround for the slit receptors that they found in area 17.

Baylor: It's a very elegant result.

Armstrong: Well, I think it's nice. I have always thought that I would like to return to work on that at some point. So anyway, that was my introduction to electrophysiology at Washington University. And following that I interned for a year at the University of Chicago and then came back for a short time to Washington University and was fortunate enough to find a place in Kacy Cole's lab at the National Institutes of Health.

Part 4: Leaving Medicine for Scientific Research
Armstrong describes why he left medicine to join Kacy Cole's lab at the NIH. Later, he and his wife work in the lab of Andrew Huxley in London. Next, he went on to Duke and then Rochester before arriving to stay at the University of Pennsylvania.

Baylor: Now was it a difficult decision to leave medicine and go into science, or was it easy?

Armstrong: For me it was not a difficult decision. I had decided that, again, my mind was just not the right sort for medicine. That I preferred dealing with things that were idealized and less empirical. I think also the general tenor of the discussions that one had on (medical) rounds was somewhat difficult for me, because it was all focused on showing that one had read the latest articles in the medical journals. So it struck me as somewhat too empirical, and I think that my inclination was to try to improve the basis for understanding some of these things. I might say that I keep watching these things, and there has been unbelievable progress in many fields. It really makes me proud to be a part of the medical science endeavor to see just how rapidly things are changing. Immunology is one of the specific cases that I can think of. Immunology sounded, when I first heard about it in medical school, like something that I didn't want to know anything about. But now it is, after many years of effort, a wonderful story.

Baylor: Right. So you went back to Washington briefly and then went to NIH to Kacy Cole's lab—the lab of biophysics. And that must have been very exciting.

Armstrong: Oh, that was absolutely wonderful. For one thing, it was, of course, a complete change of surroundings. I'd gone from Texas to the Far East, as I saw it, and of course everything was different. Washington was a wonderful place to be. The entire atmosphere there was extremely stimulating. So I felt very fortunate to be able to go to NIH. NIH at the time was really a wonderful center, which was very helpful in stimulating the development of medical research in the universities and medical schools. It played a very key part, and I happened to be there just at one of the very best times imaginable.

Baylor: And then from NIH it was to Andrew Huxley's lab?

Armstrong: Yes. And that was also a wonderful learning experience. Huxley was really a very exceptional man. He was so brilliant, with such a powerful mind, and so imaginative in his experiments. The list of his accomplishments is really quite staggering.

Baylor: So you worked with him for about one year, was it?

Armstrong: Clara was also working in his lab, and we were there for two years. He was quite busy at the time as department chairman, so the experiments really didn't quite get started, but as a learning experience it was really spectacular. The reason that the experiments didn't get started, I might say, is that I had to learn how to dissect single muscle fibers, which is very hard. So it was my deficiency as a dissector. Although I had learned to dissect squid axons by that time, muscle fibers were something else. It was difficult to get a very good experiment out of the fibers that I could produce.

Baylor: So from UCL (University College London) you went to Duke and then to Rochester?

Armstrong: Yes. Duke at the time was a very important place in American physiology. Dan Tosteson was the chairman and Paul Horowitz was a huge attraction for me. And it was a wonderful department. Certainly one of the best that I've encountered. Again, a very stimulating time. John Moore was there working on ion channels, and so we loved it at Duke. It was a very good place to work. We then followed Paul Horowitz to Rochester and that again was a wonderful place to work. Paul's department was splendid. So many friends from those institutions. And in the winters, one of my connections at the time from both Duke and Rochester was with Chile. I had first gone to Chile when I was at NIH in Kacy's lab...

Baylor: In search of squid.

Armstrong: Yes, in search of squid. And there were two big inducements to go to Chile. One was that the atmosphere was very lively. They were a wonderful group. The Chileans have crazy work schedules. They work all the time and they're very lively. So that was one big attraction. Then the other was that they had squid that were just very large so that it made the dissection of the axons and the performance of the experiments very easy. It was there in Chile that I first encountered Pancho, who is one of the best things that every happened to me.

Baylor: Wonderful colleague.

Armstrong: Yes. So then, well in brief, after approximately six years at Rochester we came to Penn and have been at Penn ever since. My connection now is not with Chile, but with the Marine Biological Laboratory (in Woods Hole, Massachusetts), which is where Clara and I met, as a matter of fact. I first went to MBL while working in Kacy's lab at NIH, and Clara and I met there. Clara at the time was a postdoc with Keith Porter. She was at Harvard, so she came down for the summer, and we met, and it was love at first sight, I guess. (Laughter.)

Baylor: And MBL is certainly a wonderful place for science, isn't it? It's stimulating, and people from all over the world come and make do even if the equipment isn't perfect. Somehow people manage to find some sealing wax and thread and make it work somehow.

Armstrong: Yes, well, that you have to do. The MBL is really one of the places of my dreams. It's very supportive from the point of view of research. People work very hard, so the reward is there all around you. It's such a beautiful place. I think that contrary to the impression that people go to play tennis and enjoy the beach, I think that although those things are there, it just makes people work all the harder. So I absolutely love the place.

Part 5: Ion Channels as Definite Physical Entities
Armstrong elaborates on his early work using TEA and his collaboration with Dr. Hille.

Baylor: So Clay, could we get into the nitty gritty of your work? I think that to an outsider, one of the most striking features of what you've done is to think about the channels as definite physical entities, as little machines that work according to certain rules that are mechanistic rather than these formal entities that had been conceived before you got into it. And so I would love to ask you about how this evolves. I guess TEA played a big part in a lot of the initial thinking about how channels work and the idea that you could flush TEA out of the channels with potassium moving in and so on?

Armstrong: Um, hum. I think the way that you put it is very accurate. When I first arrived in Kacy's lab, I think that the emphasis was largely mathematical. Well, for example the ideas of pores and carriers somehow just weren't on the map. One wanted a mathematical formalism to explain what we now call gating, and Kacy at the time was trying to understand it in terms of electrodiffusion of ions within the membrane according to the Nernst-Planck ideas and formulation. Being a practical mechanical type from Texas, I tended to want to know a little more of what the conducting units as they were called at the time looked like, and so I was very attracted by the pictures given by Hodgkin and Keynes of the long pore effect. That was in existence, of course, that was part of the educational background.

Baylor: That was a wonderful mechanical model that they had with the two big containers full of balls that were being shaken back and forth.

Armstrong: Yes. That was very stimulating. I tended to immediately think in those terms. And also I was, well, lucky to some degree, but I think kind of I would have to say thoughtfully lucky in getting involved with TEA. And that I did just by going to the library and reading. I read two papers that I found to be very stimulating. One was by Hagiwara and Tasaki, and they had done something which clearly looked to an unbiased observer like they were blocking potassium channels with TEA. And that's what Hagiwara always said that he thought, but that he couldn't say it because Tasaki was too strongly against the idea of ion channels. But in any case, that was one of the papers. And the other one that I read that I thought was just wonderful was a paper by Dennis Noble about anomalous—which subsequently became inward—rectification in the heart. I was very stimulated by that paper and decided on the basis of quantitative measurements given in the paper of Hagiwara and Tasaki that the potassium channels must be behaving as inward rectifiers. So well, then the attempt was on to prove it using squid axons during the summer, and it eventually worked out. Certainly it didn't seem for quite some time, of course, that it was going to. But Leonard Binstock and I were performing experiments together, and we indeed discovered that if the potassium concentration was high on both sides and TEA was present on the inside, that the potassium channels behaved like inward rectifiers.

Baylor: That must have been very exciting.

Armstrong: Oh, that was terrific.

Baylor: You were immediately then thinking that the potassium moving inward was knocking the TEA out of the channel?

Armstrong: Well, I was trying to imagine what TEA could be doing, so I made a CPK model of TEA and discovered that basically it couldn't be doing very much, because it's kind of a little solid pyramidal chunk with its central nitrogen and four ethyl arms, and the arms are not very movable. So it is basically a little pyramid that moves through the solution and can't assume any very interesting conformations. And its similarity in size to a hydrated potassium was very suggestive. So the picture of the TEA lodging in a channel that was big enough to accept it as its inner end and (that) then narrowed down was immediately irresistible. And so after that, I guess I never looked back. It seemed that the channel had to be the way. But it was a long time before, I think, people were willing to accept this—that it was a channel rather than a carrier—because, of course, I guess it was the late '60s early '70s (that the carrier) Valinomycin was discovered. I'm a little vague on the precise date. But in any case it was potassium selective, and I think many people assumed that was going to be the answer to the potassium selectivity problem. We even managed with TEA to get a reasonably good estimate of the channel conductance, because one could measure the rate of entry of TEA if the concentration is sufficiency low. And then just by multiplying, scaling it from the concentration ratio (potassium/TEA), you could get an idea of how fast potassium was entering. And that turned out to be roughly one per micro-second. TEA, in fact, doesn't seem to enter quite as readily as potassium, as we now know. But anyway, that gave an idea that the conductance of the conducting unit, which was still not known to be pore or channel, had to be pretty high, much more consistent with a pore than a carrier.

Baylor: Right, right. And I suppose the TEA then was in the back of your mind when you conceived the ball and chain mechanism for inactivation?

Armstrong: Well, yes, there was another step involved, and that was my favorite experiment, I think probably of all time, that I was involved with. And that was the TEA derivatives, which replaced one of the ethyl arms of TEA with a hydrophobic arm that was substantially longer. And nine carbons rather than two was my favorite…the triethylnonyl ammonium ion. I started lengthening the arms with the idea that I would perhaps learn something about the rate of entry because it should then depend on the orientation of the molecule. But the results were much more interesting than my expectation because it immediately became apparent that these were blockers of much higher potency (than TEA). They had such a high affinity for the channel that it was possible to see inactivation because they could be used at very low concentrations. And then (at low concentration) they entered the channel quite slowly and produced what certainly looked very much like sodium inactivation, but in a potassium channel. Well, there are lots of details in those experiments that I really liked, for example, that you could knock the ions out by raising the potassium concentration on the outside, having applied these things (TEA derivatives) to the inside. And well it all seemed to fit quite well with the general idea that the pore had a wide inner mouth and then narrowed so that the TEA derivative couldn't work its way through, since it was not possible for it to lose its covalently attached arms. So that gave then a nice clue with regard to the selectivity mechanism of the channel, that the ion seemed likely to be dehydrating.

Baylor: Yes. So (regarding) the ideas about selectivity, I gather you interacted a fair amount with Bert Hille around that time.

Armstrong: Yes. I can't remember precisely when I first met Bert, but it must have been in the late '60s and after I had come back from London. And Bert was—well, I have very fond memories always of having interacted with Bert. He's extremely stimulating and always a person of very great integrity and wonderfully imaginative. He and I were working to some degree on the same things. He tended to favor the sodium channel and TTX (tetrodotoxin), and there were his wonderful contributions on the actions of both of those substances (TTX and TEA) on the myelinated fibers. And then his great work on selectivity, which still provides the best model of selectivity of the sodium channel, and the local anesthetic work. And then there's, of course, his great book, which is extremely influential.

Baylor: Yes. It's really a wonderful source, isn't it?

Armstrong: It is. It definitely has you might say paved the road for ion channels. Bert and I even worked together once upon a time in Seattle, which was a beautiful occasion. He took me out to the see the salmon there as they were running in the fall. And we applied some of the long chain TEA derivatives to the inside of a myelinated fiber and found out, in short, that they behaved pretty much the same with regard to the internal quaternary ammonium receptor, TEA receptor, like the squid axon. But the squid axon did not have an external TEA receptor at all, while the external TEA receptor in the case of the myelinated fiber, the frog myelinated fiber, was quite different in character (from the internal). It didn't interact with the long chain compounds effectively at all. So it looked as though quite clearly there were two separate TEA sites, one at the inner end and one at the outer end, and they had different properties. And, of course, we now know that the external TEA sensitivity is assignable to a single tyrosine residue in each sub unit of the potassium channel, the work of Rod MacKinnon and colleagues.

Part 6: Ball and Chain Mechanism
Armstrong outlines his development of this mechanism for inactivation of channels, as well as his gating current experiments.

Baylor: I think the ball and chain mechanism for inactivation of channels was truly a remarkable idea. And it's one of the few cases where somebody had such a radical idea that then turns out to be more or less exactly right. I'm still staggered that that worked so well. (Laughter.)

Armstrong: Well, I was also surprised, I might say. But obviously very pleased. The chain of thought was quite simple and that is having been presented with these experiments on TEA derivatives causing inactivation of the potassium channel and having found that pronase can remove inactivation from the sodium channel, when applied to the inside of the sodium channel, well it (sodium channel inactivation) certainly seemed easily explainable by saying that there is something analogous to TEA, some inactivating particle analogous to a long chain TEA molecule, that is tethered there at the inner end of the sodium channel. And we even got the stoichiometry of it right, by the way, from the pronase experiments because the time constant of the inactivation didn't change. So it looked like one hit on each of the sodium channels, and that seems to be the case since (in) the sodium channel (inactivation) now resides by all accounts in the 3-4 domain linker.

Baylor: Right. So I guess an important part of the ball and chain mechanism was the idea that the channel had to open before the ball could go in and get stuck in the throat of the channel. And this was against what Hodgkin's and Huxley's picture had been and there must have been a fair amount of flack that you encountered as a result of that idea.

Armstrong: Well, pleasant flack. I mean it was flack from people who were basically extremely nice. But yes, it was...Well that was a big emotional step, too. I, of course, was convinced that it was right, but then I kept thinking well, you know, what is there to go on? So the first experiment to try and see if sodium inactivation had similarities was to see if one could see a lag in inactivation that was consistent with the idea that the channel had to open before it could inactivate. I managed to measure that on an axon down in Chile and had an abstract in the Biophysical Society in 1969 that, in fact, got the story more or less right (chuckles). It said that it looked as though two of the three Hodgkin and Huxley particles had to move in order for the channel to be able to inactivate. In fact, there is some inactivation apparently before the channel fully opens. But I didn't really pursue that very strongly because I felt that it would be so easy for Hodgkin and Huxley to simply, let's say, raise h (the inactivation variable) to the second power and thereby provide a lag in the inactivation. So I didn't quite know what to do. The pronase experiment and then subsequently the gating current experiment turned out to be the way to proceed.

Baylor: Well, the gating current experiment was really wonderful because it showed directly that the gating charges do interact with the inactivation process and that charges become immobilized when the inactivation takes place.

Armstrong: Yes, that's what we ultimately discovered. We started on the gating current experiments, I think along in the early '70s. Of course, the existence of gating current was a prediction of the Hodgkin and Huxley scheme. If one thinks about it, there really is no alternative. If there is a voltage sensitive channel, then there has to be some charge movement associated with the structures that sense the change in the voltage.

Baylor: It's interesting, though, that I remember in the early '70s, before you found the gating current, Hodgkin saying that he thought that there ought to be a gating current. He couldn't imagine how it would work otherwise, but he was so worried about whether it would really be there or not.

Armstrong: Yes. Well, there were several attempts to measure it. Knox Chandler and Hans Meves, for example, had made an attempt to measure gating currents. And then I think that if you look at one of their illustrations, they actually had it, but they thought they didn't. But there is something that I think now one would call gating current. And Hans continued to work on it, and I think Richard Keynes was intending to work on it. And Eduardo Rojas was in England at the time, and so he communicated some of this fervor to Pancho and to me. And so we actually started working on it. We did our first experiment, in fact, with Eduardo, and I don't think that one worked very well. Pancho and I got back to it sometime later and worked very hard, and that was an interesting, very lively time.

Baylor: Definitely. I remember the Cold Spring Harbor meeting in 1975 when you spoke about the gating currents and Eduardo Rojas spoke, and there was a certain amount of flack that went both directions. In fact, it was in some ways the highlight of the meeting that people could sit and see these two different groups with fairly different results.

Armstrong: Yes, well, it was stimulating, also somewhat embarrassing, since we were all supposedly professional, competent investigators, and we couldn't get the elementary facts of the (gating current) behavior quite straightened out. But that, I think, must be the way these things go. I'm very proud to say that Pancho and I, I think, were right on all counts. And Richard Keynes at one time was extremely generous, I think, in basically admitting that. I wasn't present at the Gordon Conference where he talked and said, I was told, that he'd come in sack cloth and ashes for Keynes and Rojas. But I thought that was really an extremely graceful gesture. Characteristic, I might say, of the general type of person who has always worked in the field. It's a wonderful group of colleagues that I've had in working on ion channels. The pressure was really quite strong and many people were interested and wanted to know precisely, exactly how it worked. And that was a matter of detailed empirical description and not so easy to come by. So we worked for a long time and finally, I think, two of the major facts that we discovered were that the m system of Hodgkin and Huxley, the idea that there are three independent particles that move during the activation of a sodium channel did not seem to fit well with the turning off kinetics of the sodium channel. And the other was the finding that the gating current tails during the deactivation as the channels were turning off on repolarization, that those tails were not independent of inactivation as was predicted by the Hodgkin and Huxley model.

Baylor: Right. So the idea was that the ball was stuck in the pore and that this paralyzed the movement of the gating particles.

Armstrong: Yes, yes, right. So that fit perfectly well with the idea that some particle analogous to TEA had gotten into the channel and was preventing it from closing. And we subsequently found that, in fact, it immobilized about two-thirds of the charge. Also we were able to identify charge that, at least in theory, would make the channel nonconductive so that it did not reflux through the open state during recovery from inactivation.

Part 7: Zipper Idea
Armstrong comments on the origin and confirmation of this idea and concludes with encouragement for young scientists to enter the channel field.

Baylor: So how was it that you went from the charge movement, the thing that you measure with electrical techniques and stuff, and then came up with the idea of the zipper scheme for what the charge movement was representing structurally?

Armstrong: Oh, well, that was just, I guess, a lucky guess. After the gating current experiments and the quaternary ammonium experiments, I felt that inactivation was really fairly well solved from the conceptual point of view. I really thought that that had to be more or less right, that there was, in general terms, a conformational change that was associated with the opening of the channel and that that had to occur before something (the inactivating particle) could diffuse into the mouth of the channel and block it. And so that took care of an inactivation. It was clear from that experiment and from the TEA experiment that the gate had to be on the inside and it was, of course, abundantly clear since the time of Hodgkin and Huxley that the gate had to be voltage sensitive, and that that meant that there was charge movement, and now the charge movement had been identified. But to decide precisely how the charge moved was something of a problem. And so the zipper idea came from the notion that, well, one didn't want the conformational change to be too large—that the idea of a particle moving all the way through the membrane seemed unattractive.

Baylor: Yes. So the minimal structural change that you could get away with and still have the gating current, sort of?

Armstrong: Yes, right. And that seemed to be best fit by the idea of having many charges moving simultaneously, each one of them through a small part of the electrical field. Let's say if you had seven charges in a row, each of them could move a seventh of the way through the field for an equivalent electrical charge movement of one electronic charge.

Baylor: But this idea of the zipper then was, in a general way, confirmed very beautifully when the channels were cloned and when the S-4 region was identified. So this then formed a nice structural basis for the zipper.

Armstrong: Yes. I felt like someone upstairs was being good to me. (Laughter.)

Baylor: That, and then when Aldrich and his colleagues found the mutagenesis evidence for the ball and chain model, that's again one of my very favorite confirmations of one of your ideas.

Armstrong: Well, that was a series of very lovely experiments by Rick and Bill Zagotta and Toshi Hoshi. Yeah, that was spectacular. So I had a double interest, both because it was such beautiful work and also because it seemed to fit this old idea of the ball and chain model. So that was lovely. Well, of course, the picture (in the channel field) has now changed completely, what with the patch clamp and cloning, and that provided wonderful new tools. The patch clamp has allowed us to look at all cells. No longer can you just look at the squid cell, squid axon, but any cell is now a reasonable target for electrical investigation. So that's wonderful. And the cloning, of course, knowing the sequence of the channels, well, has lead to such wonderful things as the inactivation experiments of Rick (Aldrich) and his colleagues. And then the identification of the P region by MacKinnon and Gary Yellen, all starting in Chris Miller's lab.

Baylor: And that's all now moving forward at an ever-accelerating pace.

Armstrong: Yes, yes. So it's dizzying to try to keep up with it. But the quality of the people working in the field is just staggering. I mean Rod and Gary Yellen and, well, Chris and Pancho and Rick Aldrich and Zagotta and Dick Horn and Isacoff and, oh, there are so many that I can't name them all, but they're all fantastic.

Baylor: It is really science at its very, very best. It's a wonderful field.

Armstrong: I feel very pleased to have been in it.

Baylor: Definitely. Now would you recommend that a young person today go into this field, or in fact should a young person go into science? The type of science that you have done?

Armstrong: Yes! Oh, absolutely. What else is there to do? No, no, no, it's great fun. It's very exciting. Why would I tell somebody not to do it?

Baylor: It's not too risky?

Armstrong: No, I don't think it's too risky. No, not at all. I mean do you know anybody who's starving? Who is... no, you won't make millions, but you'll certainly live an interesting life.

Baylor: I agree. It's a wonderful privilege.

Armstrong: After all, money isn't everything.

Baylor: Right. Yet to find out a little something about nature is a wonderful privilege.

Armstrong: The Pleasure of Finding Things Out I think is one of Feynmann's books, and it's absolutely right. To know something that nobody else has known, it must be like being the first person to see, let's say the first Westerner to see the Pacific Ocean. It's just wonderful. And of course physical exploration is getting—there aren't too many places that haven't been seen now—but there are certainly many, many opportunities for exploring in science. And slowly, you know, increasing our general knowledge of the universe. It's, well, it's wonderful. So I would definitely say so, and also, you know, I would say to students that you don't have to start immediately. Rod and I are examples of that (late starters).

Baylor: That's right. Physicians.

Armstrong: Right. We started off as medical doctors. We didn't have very rigorous training. I think in the case of both of us, we loved to look at physics books and try and figure things out, but we weren't trained in it. So I think it's never too late to start.

Baylor: So there's hope for us all.

Armstrong: Ah. Well, yes, right. I think it is an extremely rewarding life, much more so than, well, I guess I better not use examples. (Laughter.) But I like it.

Baylor: So, Clay, it's been a pleasure to talk to you about this stuff. It's a fascinating insight into your career, and into the channels, and what a pleasure.

Armstrong: Well, Denis, for me being interviewed by you is an enormous pleasure. Someone that is such an accomplished scientist and someone with such an excellent understanding of all of these matters and such—well, your experiments, of course, are the admiration of the world. So thank you very much for taking the time to do this, Denis.

Baylor: Well, it's my pleasure, and thank you, Clay. Look forward to talking to you again.