Long-term regulation of catecholamine formation by ouabain in cultured bovine adrenal chromaffin cells

The long-term effects of ouabain, an inhibitor of Na+/K+-ATPase, on catecholamine formation in cultured bovine adrenal chromaffin cells were examined. The increase in [C-14]catecholamine formation from [C-14]tyrosine induced by ouabain was dependent on incubation time, and its maximal effect was observed after incubation for 8 h. The stimulatory effect of ouabain was concentration dependent (10-300 nM), causing maximal stimulation at 300 nM. The formation of [C-14]catecholamines induced by ouabain was not increased by incubation with [C-14]DOPA instead of [C-14]tyrosine. Ouabain-induced [C-14]catecholamine formation was influenced by decreases in extracellular Ca2+ concentration, but not bq the presence of cycloheximide or actinomycin D. These results suggested that ouabain stimulates continuous activation of hydroxylation of tyrosine through a Ca2+-dependent mechanism in cultured bovine adrenal chromaffin cells.