Ionic and metabolic requirements for stimulation of secretion by ouabain in bovine adrenal medullary cells

The effect of ouabain on the secretion of catecholamines from isolated bovine adrenal medullary cells was investigated. Ouabain enhances the basal rate of secretion approximately 2-fold, with half-maximal stimulation occurring at a glycoside concentration of around 5 X 10(-7) M. Parallel measurements of the release of dopamine beta-hydroxylase (EC 1.14.17.1) (an enzyme associated with chromaffin granules) and lactate dehydrogenase (EC 1.1.1.27) (which is confined to the cytosolic compartment) suggest that this increase in secretion occurs as a result of an enhanced rate of exocytosis rather than by any other route. The stimulatory effect of ouabain is dependent on extracellular sodium but is maintained in the nominal absence of calcium and is unaffected by changes in the major external anion. Neither tetrodotoxin nor phenoxybenzamine alters the response to glycoside treatment, but the calcium channel blocker methoxyverapamil reduces the catecholamine secretion evoked by ouabain in a dose-dependent fashion. This study serves to characterize the secretory action of ouabain in isolated chromaffin cells and to provide a foundation for the ion flux studies reported in the following paper.