PLATELET AND ERYTHROCYTE MG2+, CA2+, NA+, K+ AND CELL-MEMBRANE ADENOSINE-TRIPHOSPHATASE ACTIVITY IN ESSENTIAL-HYPERTENSION IN BLACKS

Objective: To assess the relationship between intracellular Mg2+, Ca2+, Na + and K + and cell membrane adenosine triphosphatase (ATPase) activity in normotensive and hypertensive blacks. Design: Intracellular cations and cell membrane ATPase activity were studied in black patients with untreated essential hypertension and age-, weight- and height-matched normotensive controls. Platelet, erythrocyte and serum Mg2+, Ca2+, Na+ and K+ levels as well as platelet and erythrocyte membrane Na+,K+-ATPase, Ca2+-ATPase and Mg2+-ATPase activities were measured in all subjects. Methods: Intracellular Na+ and K+ were measured by flame photometry and Mg+ and Ca+ by atomic absorption spectrophotometry. Cell membrane ATPase activity was determined by a colorimetric method. Results: The hypertensive group consistently demonstrated depressed activity of each ATPase studied, with significantly lower serum Mg2+, serum K+, erythrocyte Mg2+ and platelet Mg2+ levels compared with the normotensive group. Platelet Na+ and Ca2+ and erythrocyte Ca2+ were significantly elevated in the hypertensive group. In the hypertensive group, mean arterial pressure (MAP) was inversely correlated with platelet and erythrocyte membrane Na+,K+-ATPase, Ca2+-ATPase and Mg2+-ATPase. Serum Mg2+, serum Ca2+ and platelet Mg2+ were negatively correlated with MAP in the hypertensive group whilst erythrocyte and platelet Ca2+ were positively correlated. In the normotensive group, platelet Mg2+ and MAP were negatively, and erythrocyte Ca2+ and MAP, positively correlated. Conclusions: Black patients with essential hypertension have widespread depression of cell membrane Na+,K+-ATPase, Ca2+-ATPase and Mg2+-ATPase activities with serum and intracellular Mg2+ depletion and cytosolic Na+ and Ca2+ overload, which may reflect an underlying membrane abnormality in essential hypertension. These cellular abnormalities may be related to the defective transport mechanisms that in turn may be aggravated by Mg2+ depletion.