Na-K-adenosine triphosphatase and cation content in the erythrocyte in essential hypertension

We measured ouabain-sensitive and ouabain-resistant Na-K-adenosine triphosphatase (ATPase) activity in the red cells of 25 normotensive (average mean blood pressure [BP] 90.2 +/- 1.27 mm Hg) and 29 hypertensive subjects (average mean BP 115.3 +/- 2.45 mm Hg). Intracellular Na and K content were measured in 13 of the normotensive and 19 of the hypertensive subjects. All subjects were male, black, of comparable weight, and had not received antihypertensive medications for at least 30 days. Ouabain-sensitive ATPase activity was found significantly lower in the hypertensive than in the control group (140.2 +/- 11 and 97.6 +/- 7.6 nmol/mg/hr, respectively, P = 0.0008), whereas no significant difference in ouabain-insensitive ATPase was observed. Intracellular Na concentration was higher (9.47 vs. 7.24 mmol/L, P = 0.0144), and intracellular K concentration lower (82.8 vs. 88.8 mmol/L, P = 0.0425) in the hypertensive subjects. These results are consistent with diminished activity of the Na-K pump in black males with essential hypertension who have received no treatment.