Calcium channels do not play a role in the steroid response to ACTH IN Y1 adrenocortical cells.

Overview

Y1 cells derived from mouse tumor zona fasciculata cells (ZF) were used to assess the importance of extracellular (EC) calcium availability via voltage-dependent calcium channels (VDCC) on steroidogenesis. The steroidogenic response to ACTH was investigated in the presence of blockers known to affect both calcium and potassium channels in Y1 cells. Y1 cells respond to either ACTH (100 pM) or cAMP (300 microM) at low EC Ca2+ (1 microM) suggesting that EC Ca2+ is not absolutely necessary for a steroidogenic response. However, increases in Ca2+ from 0.05-2.2 mM induced a small but significant biphasic response, first stimulating then inhibiting steroidogenesis. Nickel and amiloride, blockers of T-type Ca2+ channels in Y1 cells, did not depress ACTH-induced steroidogenesis. The dihydropyridine, nifedipine, which is an L-type channel antagonist did not affect ACTH-induced steroidogenesis while the agonist, Bay K 8644 was consistently inhibitory. Neither pimozide nor omega-conotoxin which suppressed Ca2+ currents in Y1 cells inhibited ACTH-induced steroidogenesis. Depolarization of the membrane which would activate VDCC's was inhibitory rather than stimulatory. The present studies using blockers of both voltage-dependent Ca2+ and K+ channels suggest that EC Ca2+ plays a modulatory role in ACTH-induced steroidogenesis in Y1 cells but the data do not support the concept that activation of voltage dependent calcium channels are an important mechanism for steroidogenesis.