Generation of plasma membrane potential by the Na+-pump coupled to proton extrusion.

Lettré cells maintain a plasma membrane potential near -60 mV, yet are scarcely depolarized by 80 mM Rb+ and are relatively impermeable to 86Rb+. They are depolarized by ouabain without a concomitant change in intracellular cation content. Addition of K+ to cells suspended in a K+ free medium, or of Na+ to cells in a Na+ free medium, hyperpolarizes the cells. They contain electroneutral transport mechanisms for Na+, K+ and H+ which can function as Na+:K+ and Na+:H+ exchanges. It is concluded that plasma membrane potential of Lettré cells, in steady-state for Na+ and K+, is produced by an electrogenic Na+ pump sustained by electroneutral exchanges, and restricted by anion leakage.