Effects of pH, potential, chloride and furosemide on passive Na+ and K+ effluxes from human red blood cells.

Ouabain-resistant effluxes from pretreated cells containing K+/Na+ = 1.5 into K+ and Na+ free media were measured. Furosemide-sensitive cation effluxes from cells with nearly normal membrane potential and pH were lower in NO3- media than in Cl- media; they were reduced when pH was lowered in Cl- media. When the membrane potential was positive inside furosemide increased the effluxes of Na+ and K+ (7 experiments). With inside-positive membrane potential the furosemide-insensitive effluxes were markedly increased, they decreased with decreasing pH at constant internal Cl- and also when internal Cl- was reduced at constant pH. The correlation between cation flux and the membrane potential was different for cells with high or low internal chloride concentrations. The data with chloride greater than or equal to 47 mM showed a better fit with the single-barrier model than with the infinite number-of-barriers model. With low chloride no significant correlation between flux and membrane potential was found. The data are not compatible with pure independent diffusion of Na+ and K+ in the presence of ouabain and furosemide.