Intracellular sodium, potassium and magnesium concentration, ouabain-sensitive 86rubidium-uptake and sodium-efflux and Na+, K+-cotransport activity in erythrocytes of normal male subjects studied on two occasions.

The red cell Na+,K+-ATPase pump activity estimated by the ouabain-sensitive 86Rb-uptake or Na+-efflux, the Na+,K+-cotransport activity measured either by the furosemide-sensitive K+- or Na+- efflux or by the ethacrynic acid-sensitive 86Rb-uptake as well as the intraerythrocyte concentration of sodium, potassium and magnesium were studied in 29 normal male subjects with one to three weeks interval between the first and second blood sampling. Both the red cell sodium and potassium concentration, the erythrocyte ouabain-sensitive 86Rb-uptake and Na+-efflux, the furosemide-sensitive Na+- and K+-efflux and the ethacrynic acid-sensitive 86Rb-uptake are stable over time in the same individual. The furosemide-sensitive Na+-and K+-efflux is significantly related to the ethacrynic acid-sensitive 86Rb-uptake. The intraerythrocyte Na+ concentration was negatively related to the ouabain-sensitive 86Rb-uptake, but not to the ouabain-sensitive Na+-efflux; it was, however, negatively related to the rate constant for the ouabain-sensitive Na+-efflux.

Methodological assessment of assays for intracellular concentration and transmembrane fluxes of sodium and potassium in erythrocytes of man.

The reliability of the assay of intracellular Na+ and K+ concentration; Na+,K+-ATPase activity; Na+-K+ cotransport and Na+-Li+ countertransport in erythrocytes was investigated. These assays were also applied in normal male subjects with and without family history of hypertension. The various assays are reproducible as indicated by the intra-assay variation and are stable over time as shown by the inter-assay variation. A delay between blood sampling and analysis, however, result in an increase in intracellular Na+ concentration and decreases in Na+,K+-ATPase activity; Na+-K+ cotransport and Na+-Li+ countertransport. Compared to the white normal males without family history of hypertension (n = 43) red blood cells of white normal males with such a history (n = 17) have a higher (p less than 0.01) intracellular Na+ concentration. This can be at least partly due to their lower (p less than 0.001) furosemide-sensitive Na+ efflux rate. Also, their ouabain-resistant 86Rb-uptake was lower (p less than 0.05). The potassium concentration in the red blood cells was similar in both groups.