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

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Abstract
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 NO 3 − 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 thefurosemideinsensitive 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≧47mm 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.