The figure below illustrates some possible realistic intracellular and extracell

Question

The figure below illustrates some possible realistic intracellular and extracellular concentrations of charged solutes, where A- represents other permeant and impermeant anions and C+ represents other cations.

Intracellular:
20mM Na+
140 mM K+
35 mM Cl-
15 mM A-

Extracellular:
150mM Na+
5mM K+
5mM C+
140 mM Cl-
20mM A-

Calculate the equilibrium membrane potentials (the nernst potentials) for Na+, K+, and CL- in this system. Be certain to indicate "inside positive" or "inside negative" in your answers. Alternatively, make a convention statement such as "All values of membrane electrical potential are expressed as inside with respect to outside (ground)"

E NA+ =
E K+=
E Cl-=

Explanation / Answer

First add up everything you have on the outside then everything you have on the inside. You should find that (+) charges are in equilibrium (due to Na+ & K+ being constantly moved in & out of the cell). From here you should be able to determine what the resting potential is and whether the inside or outside is more negative. For Eq potentials: E = (RT/zF)*ln(ion outside/ion inside) Remember: R = ideal gas constant T = temp F = Faraday's constant z = # of moles transferred Calculate E for each ion.

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