What happens to the Na+ ions during an action potential?

[Renge Ishyo]

This marvelous membrane capacitor.
A single cm² that carries 1µF. That is clearly extraordinary and may make a furious envy to many electronics suppliers.

Most of natures inventions are far superior to our own in design, function, and economy. Let's face it, God (or if you prefer, "Random Mutation Man") is simply a better engineer than we are.

Please take a moment to write out a coherent post discussing *your ideas*. Because right now I feel like I am chasing a moving target.

I noticed a post or so ago that it seemed as if the target of the debate isn't always the same thing. I don't think the conversation is exactly moving in circles though, the randomness of the conversation has definitely increased from page to page indicating that the conversation is evolving in a quite natural way.

Of course, I should mention at this point that I DO have a bottle of special mineral water for sale if anyone is interested...

 

[somasimple]

The chase is prohibited. I belong to a protected specie.
Unable to give the results about simple experiments? Some reasonable doubt insinuated into your mind?
Perhaps you need some more:
Did they remove the ions channels when they measured the membrane capacitance? No, because they didn't know they were there. But you know it!
Electroneutrality: Even Roderick MacKinnon is aware of ions hydration (just see the pictures provided in the Nobel Lecture). That makes a big problem to a polarized membrane as a capacitor since you must solve its boundaries limits: Does the violation stops at 0.5 nm, more, less but how? What is the effect of hydration on charged particles?

Please forget your cynicism and re-adopt a scientific profile: examine the facts and conclude by yourself.

 

[Dale]

Did they remove the ions channels when they measured the membrane capacitance? No, because they didn't know they were there. But you know it!

Why do you think the presence or absence of the ion channels would significantly change the capacitance of a membrane?

 

[somasimple]

Capacitance was measured with voltages/currents and there is voltage gated ions channels embedded in membrane.

 

[Dale]

So what? That would change the conductance, not the capacitance. Conductance is a current which is proportional to a voltage, capacitance is a current which is proportional to the derivative of a voltage.

 

[somasimple]

And does a capacitor have latency?
So what?
And our conductances aren't linear at all!

 

[Dale]

Your statement is unclear. The conductance of the membrane is a non-linear function of time and voltage. But conductance itself is a linear relationship between voltage and current. Do you understand the distinction? If not I will try again since I know there is some language barrier.

Also, what is the relevance to measuring the capacitance?

 

[Dale]

This marvelous membrane capacitor.
A single cm² that carries 1µF. That is clearly extraordinary and may make a furious envy to many electronics suppliers.

By the way, this is rather silly. We make phospholipid bilayers synthetically all the time and they regularly approach this capacitance. In fact, the capacitance is used as an easy metric to test the quality of the synthetic membrane.

Electronics suppliers are in no way furious or envious. They know about this technology and could generate as much phospholipid membrane as they like. The reason they don't is because such capacitors would be rather delicate and temperature sensitive as well as having low maximum-voltage ratings.

 

[somasimple]

I understand clearly the differences but I do not understand why you refuse to reply to previous questions and give results from experiments that costs less than 1$ each.

OK, let's suppose that membrane is a capacitor:
1/ Where are the metal planes?
2/ Where are the wires?
3/ In a capacitor, current flows through wires and circuit, is it the same with membrane?
4/ In a capacitor, dielectric insulates the two metal plates. In membrane, dielectric allows the whole currents fluxes, why?
5/ In a capacitor current is made from electrons, is it the same?
6/ In a capacitor, the distributed charges are symmetric, is it the same?
7/ in a capacitor, exchanges occur exclusively (except leakage current) through wires and are vertical, how are you able to enable also (in propagation) a transversal one and what rules does it follow?
8/ In your schematic, capacitor is associated with ions channels (resistances). Since wires are in both cases situated in the "capacitor plates", how do you connect them?
9/ since AP requires only a tiny 0.04 % of available ions, why do they choose to be associated to their far neighbors from the right or the left since there is closer ones just under their entry point?

 

[somasimple]

Perhaps the last question is a bit rude, sorry: You have to work around the well known electric law: current always takes the path of least resistance. (Of course, you may find an alternative explanation that may explain that laws may be violated... (sic)).
http://en.wikipedia.org/wiki/Path_of_least_resistance

 

[Dale]

current always takes the path of least resistance.

This is a commonly-repeated phrase, but it is not true. Current always takes all paths.

give results from experiments that costs less than 1$ each.

I have no idea what you are trying to say. Why should an experiment cost less than $1?

OK, let's suppose that membrane is a capacitor:
1/ Where are the metal planes?
2/ Where are the wires?

In an electronic circuit the charge carriers (electrons) are are free to move in the metal. In the neuron the charge carriers (cations) are are free to move in the electrolyte. The electrolytical fluid takes the place of the metal.

3/ In a capacitor, current flows through wires and circuit, is it the same with membrane?

Yes. However there is also leakage current which occurs across the membrane as well as in commercial capacitors

4/ In a capacitor, dielectric insulates the two metal plates. In membrane, dielectric allows the whole currents fluxes, why?

What do you mean?

5/ In a capacitor current is made from electrons, is it the same?

No, the charge carriers are primarily cations as I mentioned above.

6/ In a capacitor, the distributed charges are symmetric, is it the same?

Yes.

7/ in a capacitor, exchanges occur exclusively (except leakage current) through wires and are vertical, how are you able to enable also (in propagation) a transversal one and what rules does it follow?

Please try again, there is a language problem and I didn't understand what you are asking. What are you trying to say with the word "vertical"?

8/ In your schematic, capacitor is associated with ions channels (resistances). Since wires are in both cases situated in the "capacitor plates", how do you connect them?

No, the capacitor represents the capacitance of the membrane. The resistors represent the concudtance of the ion channels. And the batteries represent the Nernst potential of the bulk concentration gradients.

9/ since AP requires only a tiny 0.04 % of available ions, why do they choose to be associated to their far neighbors from the right or the left since there is closer ones just under their entry point?

What do you mean by "associated to"? And what do you mean by "under their entry point"? Is this somehow related to the "vertical" from above?

Please try to take things slowly. Your questions don't seem to be unanswerable, but there is a considerable language barrier. I know it is hard to express things in a forigen language, and your English is much better than my French, but even so it is probably better to spend the effort to make one clear major question than to make 9 confusing or minor questions.

In any case, the bottom line is that the HH model works quite well. You are certainly free to propose a model which works even better, but in the absence of a better model it is somewhat silly to object so strenuously to this one.

 

[somasimple]

This is a commonly-repeated phrase, but it is not true. Current always takes all paths.

I will reply to the first statement because the subsequent responses will be useless if you do not solve this one.
Yes, current flows in all paths but prefers the least resistances.
So you admit the situation but I said I wasn't kind and it was a rude question.

So we said that entering ions are associated with their opposite counterions. The most of them are just under and some will make the job onto the right and onto the left.

NO! It can't work at all.

If I accept that a ion is associated in the internal milieu of the cell, I must also accept it was also the case, outside. That makes a big problem. You must, now, consider, that ions were also associated, outside.

Then, you must also fill the gap of initial conditions (IC); A solution where energy is low and where the model may function.
Of course, there is one with the hypothesis:
All ions are associated, on each side!
You solve the problem of electronegativity but you may encounter some bigger ones:
You have now salt crystals on each side of the cell.
Bad new for diffusion and too bad for currents: It is also a well known thing that crystals are effectively neutral but very good... insulators for the same reason.

This point of view has not my preference: I prefer water bondings for salts...

 

[Dale]

I will reply to the first statement because the subsequent responses will be useless if you do not solve this one.
Yes, current flows in all paths but prefers the least resistances.

I don't like using human psychological terms like "prefers" to describe inanimate objects. I would say that current goes through all paths, but more current goes through the path of least resistance than through the other paths. This makes it clear that current is going through all paths and still covers the essence of the "path of least resistance" concept.

 

[somasimple]

The criticism is well received but the model remains still invalid.

 

[Dale]

NO! It can't work at all.

If I accept that a ion is associated in the internal milieu of the cell, I must also accept it was also the case, outside. That makes a big problem. You must, now, consider, that ions were also associated, outside.

Then, you must also fill the gap of initial conditions (IC); A solution where energy is low and where the model may function.
Of course, there is one with the hypothesis:
All ions are associated, on each side!
You solve the problem of electronegativity but you may encounter some bigger ones:
You have now salt crystals on each side of the cell.

You still haven't explained about what you mean by "associated".

I don't understand how you make the completely random jump to salt formation. It is certainly not based on any understanding of correct physics. Do you understand how a salt crystal dissolves or forms in a good polar solvent like water?

Bad new for diffusion and too bad for currents: It is also a well known thing that crystals are effectively neutral but very good... insulators for the same reason.

I am sorry, but you are completely mistaken. Do you understand what it means for a salt solution to be an electrolyte? It means precisely that you get both ionic currents and diffusion even even with both cations and anions present in the solution. This isn't even a biological phenomenon, it is simple high-school level chemistry. The concentrations are way to low to get salt formation, and there is diffusion and electrical conduction via ionic currents.

 

[Dale]

The criticism is well received but the model remains still invalid.

No it is not invalid. It fits a wide range of experimental data within its domain of applicability. That is all that is required to validate a scientific model. I am having a hard time following your objections, but the simple fact remains that the HH model works. Therefore it is valid. End of story.

If you make any model (it doesn't have to have any physical inspiration as the HH model does), propose a hypothesis based on the model, perform the experiment, and get data supporting the hypothesis, then the model is validated. That is the nature of science.

As you perform more experiments you may get some experiments that don't match the model. Then you learn the limits of the domain of applicability for the model. That still doesn't make the model invalid within its already scientifically validated domain.

Some later person (like yourself) may come up with a better model that fits all the data including this new domain and, if the new model is valid, it must agree with the old model within the old model's limited domain. Such is the nature of the scientific method.

 

[somasimple]

I do not understand how you produce an equal charge of opposite sign when you move (i.e) a Na+ ion from outside to inside.

My attempt was clearly silly as the model.
Perhaps you think that Na+ let's a "free" electron on the opposite side?

 

[somasimple]

More simply,

with a simple example: KCl and water with a semi permeable membrane to K+. (High school).

IC:
The KCl is on the left (membrane at center).

Terminal conditions:

1. Some K+ ions are at right and
2. membrane is now polarized (becomes a capacitor).

Problem:
Describe how you obtain the second result?

 

[somasimple]

Perhaps you have been taught of something like this:

http://nerve.bsd.uchicago.edu/rp1.htm

I have an immense respect for Prof Bezanilla but I reject this model.

 

[Dale]

I do not understand how you produce an equal charge of opposite sign when you move (i.e) a Na+ ion from outside to inside.

My attempt was clearly silly as the model.
Perhaps you think that Na+ let's a "free" electron on the opposite side?

No, in an electrolyte the primary charge carriers are dissolved ions. However, I don't understand why you think moving an ion from one side to the other should "produce" an equal charge of opposite sign. Since the electrolyte is, in bulk, electroneutral you know that there is already an anion in solution for every cation. So no anion needs to be produced, they already exist in the solution.

KCl and water with a semi permeable membrane to K+. (High school).

IC:
The KCl is on the left (membrane at center).

Terminal conditions:

1. Some K+ ions are at right and
2. membrane is now polarized (becomes a capacitor).

Problem:
Describe how you obtain the second result?

Do you know the concept of http://en.wikipedia.org/wiki/Amperes_Law" to be useful. This is a very fundamental set of concepts that apply to many different systems, not just neurons. So I would most strongly encourage you to study this until you understand how the second result happens, but you will probably need to branch out beyond the links I have provided. Please, familiarize yourself with the fundamental concepts and post any follow-up questions that you have.

 

[somasimple]

I know you consider that I'm an idiot.
Consider that I'm stubborn, too!

I'm now facing with a strange behavior from your own: Every time we're close to get, at last, a reply, you change abruptly and bring a ton of useless material that has nothing to see with the current question.

So, I'll restate one more time my simple "virtual" and well known experiment:

Two compartments are separated by a semi-permeable membrane oriented to the "water" side (semi permeable for K+).
IC:
compartment one contains water.
compartment two is filled with a solution of KCl (potassium chloride). Concentration doesn't matters but we will take 40 mM.
The membrane capacitor is supposed discharged, right?
http://nerve.bsd.uchicago.edu/rp1.htm

Then,
At a time t1, since some K+ have moved and now, the membrane must carry some charges since we have a potential difference?

Please describe the charges carried on each side (if needed) of the membrane that explains it functions as a capacitor and maintains charges?
Hope the question is sufficiently clear?

 

[Cincinnatus]

It doesn't matter how many of his questions that you answer. He doesn't think there's something in particular wrong with our understanding of action potential generation / propagation in neurons. Instead he's sure that the theory is wrong for a priori reasons and will keep changing the subject until you get tired of arguing with him.

If you google him you'll see that he's done the same thing on many fora including this one several other times. It's really pretty useless to keep answering his questions as he's never going to stop and say "oh I get it now".

Somasimple, why don't you just explain your theory? (in the IR forum here) It may well be that you can explain the data as well as or better than the Hodgkin-Huxley model (and it's extensions). Why not let us judge your hypothesis in the only way hypotheses can be, by testing them with real data.

Until then, the fact remains that the Hodgkin-Huxley model is very very good at making testable predictions and works better than any other model we currently have. This alone is reason enough to think that the model is at least a good approximation to the truth.

 

[somasimple]

Cincinnatus,

The same answer may apply to you. Are you unable to describe the thing?

 

[somasimple]

If you google him you'll see that he's done the same thing on many fora including this one several other times.

And I got, every time, different explanations.

Until then, the fact remains that the Hodgkin-Huxley model is very very good at making testable predictions

We are currently testing the initial conditions of this model and you refuse to explain the next mandatory step of its functionning.

Then,
At a time t1, since some K+ have moved and now, the membrane must carry some charges since we have a potential difference?

Please describe the charges carried on each side (if needed) of the membrane that explains it functions as a capacitor and maintains charges?
Hope the question is sufficiently clear?

Giving a good answer is the best way to smash me down!
Come on, it's my pleasure.

 

[Dale]

I'm now facing with a strange behavior from your own: Every time we're close to get, at last, a reply, you change abruptly and bring a ton of useless material that has nothing to see with the current question.

It has everything to do with the current question. If you understood the principles I linked to then you would understand capacitors and how a membrane acts as one, as well as how a potential difference can be established by a chemical gradient. I take it then that you did not even bother to read what I provided.

So, I'll restate one more time my simple "virtual" and well known experiment:

Two compartments are separated by a semi-permeable membrane oriented to the "water" side (semi permeable for K+).
IC:
compartment one contains water.
compartment two is filled with a solution of KCl (potassium chloride). Concentration doesn't matters but we will take 40 mM.
The membrane capacitor is supposed discharged, right?
http://nerve.bsd.uchicago.edu/rp1.htm

Then,
At a time t1, since some K+ have moved and now, the membrane must carry some charges since we have a potential difference?

Please describe the charges carried on each side (if needed) of the membrane that explains it functions as a capacitor and maintains charges?
Hope the question is sufficiently clear?

I will restate my answer. The concentration of K+ increases until it reaches the equilibrium potential described by the http://en.wikipedia.org/wiki/Goldman_equation" across the membrane shows that it must carry equal and opposite charge density on each side. Obviously, since the charge carriers in this electrolyte are K+ and Cl-, the charges will be K+ on one side and Cl- on the other.

I hope the answer is sufficiently clear. If you have some specific question about one of the above physical principles, please don't hesitate to ask. If you merely have another rant about HH not being valid, please back it up with some experimental data that HH fails to explain and present your alternative which does explain it.

Your failure to understand HH and the underlying principles is not a valid criticism.

 

[Cincinnatus]

For the lurkers following this thread, the Goldman equation which DaleSpam refers to in the previous post is the same as the equation we had been calling the GHK (Goldman-Hodgkin-Katz) equation earlier in this discussion. It is a variant of the Nernst equation which may be more familar to some people...

Anyway, somasimple doesn't seem to accept the GHK equation as applied to biological membranes...