Intracellular concentration and transmembrane fluxes of sodium and potassium in erythrocytes of normal men and women.

The intracellular concentration and transmembrane fluxes of sodium and potassium were studied in the red blood cells of normal men and women in the two halves of their menstrual cycle. Compared to men, the intra-erythrocyte sodium concentration was lower in women during the second half of the menstrual cycle. These two groups were similar for Na+, K+-ATPase pump activity estimated from the ouabain-sensitive 86rubidium-uptake and for the furosemide-sensitive sodium and potassium efflux. Women in the first half of the menstrual cycle, had intra-erythrocyte sodium concentration similar to men, but their furosemide-sensitive sodium efflux was lower. A lower intra-erythrocyte sodium concentration was observed in the second half as compared to the first half of the menstrual cycle in women. No significant difference was observed in the intra-erythrocyte potassium concentration and transmembrane fluxes of potassium in men and women in either half of the menstrual cycle. Therefore one should take into account sex-related variability when studying cationic fluxes and concentrations in red blood cells of men and women.