Regulation of calcium influx and catecholamine secretion in chromaffin cells by a cytochrome P450 metabolite of arachidonic acid.

These studies were designed to determine the role of arachidonic acid metabolites in catecholamine secretion from adrenal chromaffin cells. Inhibitors of the cytochrome P450-dependent metabolism of arachidonic acid were shown to interfere with stimulus-secretion coupling in cultured chromaffin cells. Ketoconazole (10 microM), clotrimazole (20 microM), and piperonyl butoxide (50 microM) inhibited carbachol-dependent catecholamine secretion by 44%, 83%, and 100%, respectively; histamine-dependent secretion by 25%, 60%, and 81%, and secretion induced by 59 mM KCl depolarization by 25%, 55%, and 89%. Uptake of 45Ca2+ into the cells in response to carbachol was inhibited 63% by ketoconazole, 86% by clotrimazole, and 95% by piperonyl butoxide; KCl-dependent uptake was inhibited 7%, 56%, and 85%, respectively. However, cytochrome P450 inhibitors did not inhibit catecholamine secretion when cells were stimulated with the calcium ionophores ionomycin or lasalocid. These results indicated the involvement of a cytochrome P450 product in controlling Ca2+ influx in response to membrane depolarization. Cells prelabeled with [3H]arachidonic acid formed a 3H-labeled metabolite which comigrated with authentic 5,6-epoxyeicosatrienoic (5,6-EET) acid on reverse phase and normal phase HPLC. Pretreatment with clotrimazole inhibited the production of this 3H-labeled metabolite. Addition of synthetic 5,6-EET (1 nM) to cells pretreated with piperonyl butoxide resulted in catecholamine secretion. These data suggest a role for a cytochrome P450 metabolite of arachidonic acid in agonist-stimulated catecholamine secretion.