Voltage-activated cation transport in human erythrocytes.

We report here the effects of membrane potential on the permeability of the human erythrocyte to Na, K, and Ca. Membrane potential was changed either by varying the K concentration gradient in the presence of valinomycin or by varying the concentration gradient of the permeant anion nitrate in the presence of 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. When the membrane potential was changed from inside negative (-10 mV) to inside positive (greater than 40 mV), influx, efflux, and net flux of Na and K increased. Marked net cation loss and cell shrinkage occurred in the absence of a chemical gradient for Na and K. This voltage-dependent increase in Na and K conductance is partially inhibited by 10 microM ruthenium red and persists when the membrane potential is returned to -10 mV after transient exposure to inside-positive potentials. A similar voltage-dependent behavior was found for Ca influx. The voltage-activated Ca influx is almost completely inhibited by 10 microM ruthenium red.