Evidence for a Na‐K‐ATPase‐inhibitor in erythrocytes of patients with essential hypertension

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Abstract
ATPase activities were determined in haemolysed and dialysed erythrocytes and in haemoglobin‐free membranes of twenty patients with essential hypertension and twenty normotetisive controls. Ouabain‐sensitive ATPase (Na‐K‐ATPase) activity of haemolysate but not that of membranes was decreased in hypertensives whereas ouabain‐insensitive ATPase (Mg‐ATPase + some residual Ca‐ATPase) activity was increased in both enzyme preparations when measurements were performed in the absence of Ca2+‐chelating substances. In haemolysed erythrocytes ouabain‐sensitivity as a percentage of total ATPase activity was a good discriminator between both groups and may be a possible marker for essential hypertension. The decreased activity of Na‐K‐ATPase in haemolysate is apparently due to a non dialysable inhibitor of Na‐K‐ATPase which is either tightly bound to the erythrocyte membrane or dissolved in the cytoplasm. Following haemolysis with subsequent centrifugation the Na‐K‐ATPase inhibitor is removed, at least in part, and thus differences in Na‐K‐ATPase activity demonstrable in haemolysed and dialysed erythrocytes are no longer apparent in haemoglobin‐free membranes.