# membrane potential

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• #5840

Hi, I have a membrane potential question I really need help on.

If a cell is -55 mv and the equalibrium of K is -60 and the equalibrium of Na is 60, which way will the K move.

There is a picture of a cell with the K moving out and Na moving in (and the cell is more permeable to K than Na)

I would like to know the answer, and if I should be using the equation of E(K) = -59 log Ki/Ko

• #55638
quote darthangi:

If a cell is -55 mv and the equalibrium of K is -60 and the equalibrium of Na is 60, which way will the K move.

There is a picture of a cell with the K moving out and Na moving in (and the cell is more permeable to K than Na)

I would like to know the answer, and if I should be using the equation of E(K) = -59 log Ki/Ko

well you should indeed use the Nernst-equation and then you calculate the ratio [K+]in / [K+]out:

E = E(0) – RT/nF * ln ( [K+]in / [K+]out)

you’ll find that [K+]in > [K+]out and thus potassium will flow out.

If you want to take into account the permeability to the ions, you should use the Goldmann-Hodgkin-Katz-equation.