# Reversal potential and Equilibrium potential

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wy
Reversal potential and Equilibrium potential

Hi !

I've recorded Na+ currents from neurons and I'm trying to fit activation and steady-state deactivation curve.

External sodium conc. was 127mM and internal  was 8.6 mM.
ENa is 67.8 mV predicted by the Nernst equation
but actual extrapolated reversal potential was near +42 mV
This deviation possibly arose from contamination outward currents or non-linearity arising form Goldman-type rectification.

Here is my question.
When I fit the activation curve, which value should I use for VNa in cord conductance equation
( GNa = INa(Vm-VNa) ? ....42 mV (actual reversal potential) or 67.8 mV(preducted ENa)

W.

Bubli
Hi,

Hi,

I am having difficulty recording Na+ currents from my neurons .. .so I was wondering what solutions you used to obtain your sodium currents.

Thanks

lazy
I am not sure if my reply

I am not sure if my reply makes  sence or not.
Using smooth muscle cells, I have tried to obtain steady-state activation/inactivation curves of Na channel. In the current case, it seems to be steady-state activation curve.

I used pipette solution without sodium ions, means that the Na reversal potential is +infinitive. The experiment data showed that the curve crossed to the voltage axis and did  not show it as infinitive.

Compared with that experience, your reversal potential around +42 mV does not seem so bad as my opinion. You like to obtain the steady-state activation curve using code conductance, so I would say the actual extrapolated reversal potential should be used as VNa. Otherwise, your stady-state curve would not realize the characteristics of the channel between +42 mV and +67.8 mV.

Alternatively, I would do the same experiment without and with TTX in order to block the Na current using Cs instead of K. You should have a straight lime over the applied voltage steps which would cross to your curve (without TTX) at the theoretical reversal potential (or very close). With this, you can subtract the leak component and your stady-state curve must be more realistic.