Effect of aldosterone on the human erythrocyte sodium--potassium pump in vitro.

1. The effects of aldosterone in vitro on the Na+, K+-dependent ATPase activity of isolated human erythrocyte membranes and on rubidium (86Rb) uptake and [3H]ouabain binding of intact erythrocytes were studied. 2. ATPase activity was nearly doubled (0.061 +/- 0.006 to 0.110 +/- 0.01 mumol of Pi h-1 mg-1 of protein) by the addition of a physiological concentration of aldosterone (2.7 X 10(-10) mol/l). Higher concentrations had no greater effect. 3. Aldosterone had no significant effect on 86Rb uptake or [3H]ouabain binding. 4. Erythrocytes contain aldosterone at concentrations similar to that in plasma. The effect of aldosterone on ATPase is probably maximal.