Why does the Nernst Equation work for Resting Potentials?

Matt Jones jonesmat at ohsu.edu
Thu Jun 27 11:19:57 EST 1996

In article <ysizybla391r.fsf at sapo.usc.edu> Terrence M. Brannon,
brannon at sapo.usc.edu writes:
>My question is: don't Na+ and Cl- and the inorganic anions create a
>charge which the K+ must respond to in its passive diffusion?

I think the most precise way of solving the Nernst eqn. is to use ionic
activities rather than simple concentrations. The effective activity of
an ionic species is less than the molar concentration, and depends on
both the molar concentration of that ion and others in the solution. So
using the effective activity instead of the concentration should
compensate for the interactions with other ions and give the correct
result. Also, the charge effects are probably small at physiological ion
concentrations, so maybe using concentrations is a pretty good


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