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

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Abstract
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 (10-7 to 10-3 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

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