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Passive membrane impedance vs voltage-gated conductance

Posted: Sun Nov 04, 2018 11:20 pm
by plasticity
At subthreshold levels of injected current I am guessing that the passive membrane conductance is much greater than the conductance of voltage-gated channels. Is this true? If so then at what transmembrane potential do the voltage-gated conductances start to dominate. Bit of a newbie question!

Re: Passive membrane impedance vs voltage-gated conductance

Posted: Mon Nov 05, 2018 12:24 am
by ted
plasticity wrote:
Sun Nov 04, 2018 11:20 pm
At subthreshold levels of injected current I am guessing that the passive membrane conductance is much greater than the conductance of voltage-gated channels. Is this true?
Consider the reversal potentials of the ionic species to which the membrane is permeable. The resting potential of a cell will be closest to the reversal potential of the ionic species to which the membrane is most permeable. Proof of this true statement is left to the reader as an exercise.

Re: Passive membrane impedance vs voltage-gated conductance

Posted: Mon Nov 05, 2018 10:36 pm
by plasticity
Hi Ted

I am not sure that answers my question.

Re: Passive membrane impedance vs voltage-gated conductance

Posted: Tue Nov 06, 2018 2:15 am
by ted
Never mind--it's true only if the ionic equilibrium potentials can be regarded as fixed. It is not true if there is a permeant species whose concentrations are determined by the transmembrane potential, e.g. chloride.
at what transmembrane potential do the voltage-gated conductances start to dominate
Depends entirely on the cell. In some cases, an active ionic conductance (potassium conductance) dominates even at rest.

Re: Passive membrane impedance vs voltage-gated conductance

Posted: Tue Nov 06, 2018 3:45 pm
by plasticity
Thanks Ted!

What about for pyramidal cells? Can my question be answered definitively for them?

Cheers!

Re: Passive membrane impedance vs voltage-gated conductance

Posted: Sun Nov 11, 2018 12:28 am
by ted
No. You'd have to determine the gating properties and spatial variation of channel density of every kind of ion channel in the membrane of one cell. That cannot be done.