A Contribution of an Electrogenic Na+ Pump to Membrane Potential in Aplysia Neurons

Abstract

The resting membrane potential (RMP) of Aplysia neurons is very temperature-dependent, and in some cells increases with increasing temperature by as much as 2 mv/t. RMP at room temperature may significantly exceed the K equilibrium potential, which can be determined by measurement of the equilibrium point of the spike after potential. The hyperpolarization on warming is completely abolished by ouabain, replacement of external Na+ by Li+, removal of external K+, and by prolonged exposure to high Ca++, while it is independent of external chloride but is increased by cocaine (3 x 10-3 M). In an identified cell that shows a marked temperature dependence of RMP, both the K equilibrium potential and the membrane resistance were found to be relatively independent of temperature. The hyperpolarization on warming, which may increase RMP by as much as 50%, can most reasonably be ascribed to the activity of an electrogenic Na+ pump.