Speculate on what would happen to the resting membrane poten

Speculate on what would happen to the resting membrane potential (RMP) of a cell if the ECF concentration of K+ was 3 mM rather than the normal value. Assume all other ion concentrations are normal and the cell has normal permeability to Na+, K+, and Cl-. Do not calculate the membrane potential, but rather identify how RMP would change and justify your answer by explaining changes to gradients and resting ion fluxes.

Solution

The reference value of extracellular potassium concentration ranges from 3.6 to 5.0 mEq/L and its intracellular concentration is about 150 mEq/L. If the extracellular potassium concentration decreases to 3 mM rather than the normal value, the membrane potential becomes more negative because there will be more potassium efflux due to increased concentration gradient. This leads to hyperpolarization of the cell.