Assessment of sodium-potassium ATPase activity in human erythrocytes in vitro.

The red cell Na+,K+-ATPase pump activity was measured either by the ouabain-sensitive 86Rb-uptake in the presence or absence of 4 mM potassium in the external medium or by the ouabain-sensitive Na+-efflux in normal male subjects without any medication (n = 14) and during short-term treatment with the serotonin-antagonist, ketanserin. The ouabain-sensitive 86Rb-uptake in a medium containing 4 mM K+ was related to the 86Rb-uptake in a K+-free medium (r = 0.82; p less than 0.001) and to the Na+ efflux (r = 0.74; p less than 0.01). The intra-erythrocyte sodium concentration was negatively related to the ouabain-sensitive 86Rb-uptake (K+-free medium r = 0.59, p less than 0.05: 4 mM K+ in medium r = -0.85; p less than 0.01) and to the ouabain-sensitive Na+ efflux (r = -0.53; p less than 0.05). During serotonin antagonism with ketanserin no changes were found in the ouabain-sensitive 86Rb-uptake or Na+-efflux.