CA2-REGULATED EXPRESSION OF ALDOSTERONE SYNTHASE IS MEDIATED BY CALMODULIN AND CALMODULIN-DEPENDENT PROTEIN-KINASES()

The chronic maintenance of aldosterone production in the adrenal zona glomerulosa is associated with increased expression of aldosterone syn thase (P450aldo), the enzyme responsible for the conversion of 11-deox ycorticosterone to aldosterone. The major physiologic regulators of al dosterone production are angiotensin II (ANG II) and (K+) which act in part through increasing intracellular calcium([Ca2+](i)). Recently we demonstrated that increased [Ca2+](i) is associated with K+ induction of P450aldo expression. To determine whether Ca2+ regulation of P450a ldo is mediated through calmodulin or calmodulin-dependent kinases (Ca MK), we investigated the actions of calmidazolium (a calmodulin inhibi tor) and KN93 (an inhibitor of CaMK) on expression of P450aldo in huma n adrenocortical H295R cell line. Treatment with either calmidazolium or KN93 completely inhibited K+-stimulated expression of P450aldo mRNA with little effect on ANG II or dibutyryl cyclic AMP-stimulated induc tion of this transcript. Cellular calcium levels were also increased u sing the calcium ionophore ionomycin and calcium channel agonist Bay K 8644. These compounds increased P450aldo mRNA and this calcium induct ion was inhibited by calmidazolium and KN93. These data show that Kc-s timulated expression of P450aldo mRNA is regulated in a Ca2+ sensitive manner through mechanisms involving calmodulin and CaMK.