Effects of Ouabain on Cytosolic Calcium in Lymphocytes, Platelets and Adrenomedullary Cells

It has been suggested that a circulating inhibitor of Na/K ATPase can stimulate natriuresis and cause vasoconstriction in essential hypertension by stimulating transmembrane Na/Ca exchange to produce increased cytosolic concentrations of ionized calcium ([Ca]1) in renal tubular and arteriolar smooth muscle cells. If this inhibitor affected [Ca]1 in all cell types, then clinical assays for its presence could be applied to easily accessible cells such as blood cells or platelets, and the inhibitor could exert a hormonal action on Ca-dependent adrenomedullary secretion of catecholamines. We used the Quin 2 technique for measuring [Ca]1 in lymphocytes, platelets and adrenomedullary cells in response to ouabain. Inhibition of Na/K ATPase by ouabain (10 to 10 mol/l enhanced transient [Ca]1 responses during Ca repletion but had no effect on steady-state [Ca]1 in any of the cell lines. Although it is possible that a Na/Ca exchange mechanism may exaggerate transient increases in [Ca]1 during Na/K ATPase inhibition, other mechanisms appear to buffer these acute perturbations of [Ca]1 in lymphocytes, platelets and adrenomedullary cells