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Does the opening of a voltage-gated ion channel (i.e. the change of configuration of the protein) by an appropriate local change of the membrane potential directly and significantly alter the membrane potential in turn? Like the influx of ions that was caused by the opening of the channel does directly alter the local membrane potential?

(Assume there were no ions going through the channel: would there nevertheless be a significant change of the membrane potential by the mere opening of the channel?)

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  • $\begingroup$ Why are you interested in this question? How can you imagine a channel opening but no ions passing through? Even if we could somehow experimentally isolate this effect, why would you expect it to matter enough compared with the voltage changes due to ion flow? $\endgroup$ – vkehayas Oct 4 '17 at 9:50
  • $\begingroup$ I added "significant" in my question. Because I am not a biophysicist and my physical intuition is not strong enough, I only guess that there might be a significant change. If you say the effect is negligible ("doesn't matter enough"), that's already a valid answer. $\endgroup$ – Hans-Peter Stricker Oct 4 '17 at 10:10
  • $\begingroup$ Like others said before: if there was such an effect, you would have heard of it. Does this apply here, too? $\endgroup$ – Hans-Peter Stricker Oct 4 '17 at 10:11
  • $\begingroup$ BTW: Of course I can imagine a channel opening but no ions passing (because there aren't any around). But not under normal circumstances, that's true. $\endgroup$ – Hans-Peter Stricker Oct 4 '17 at 10:12
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Not in any substantial way from the perspective of the overall membrane potential; it could be possible to measure the charge moving as a way to study channel gating, but that's a completely separate issue (and the scale of measurement would have to be incredibly precise, way more precise than is relevant for neural function).

Although very few ions have to move across the membrane to change the membrane potential, this "very few" is in relationship to the total number of ions present in a solution, which is massive and difficult to imagine. A single ion channel can flux millions of ions per second.

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  • $\begingroup$ That's the explicit answer I hoped for (and expected) but couldn't get otherwise. $\endgroup$ – Hans-Peter Stricker Oct 4 '17 at 16:38
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I would like to add a small calculation to this question: The membrane has a large capacitance (1 uF/cm^2). A 20 um diameter cell will have a capacitance of about 50pF.

The number of charges needed to change the membrane potential in 1 mV can be calculated by:

Q=C*dV

Acording to the fromula you`ll need 0.5 pC or about 3*10^-6 elementary charges to produce a 1 mV change.

A single ion channel such as the Shaker K+ channel can move 12-13 elementary charges during activation link. This would mean activation of 3*10^6 Shaker K+ ion channels.

You can see you`ll need to have a lot of channels to do the trick.

Even though the voltage changes due to these "gating" charges is small, the current generated by the movement of these charges can be measured. They are called "gating currents".

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