VOLTAGE-DEPENDENT CALCIUM AND POTASSIUM CURRENTS IN Y-1 ADRENOCORTICAL-CELLS ARE UNRESPONSIVE TO ACTH

In this report we use both whole cell and perforated patch clamp recor ding techniques to characterize calcium and potassium channels in Y-1 adrenocortical cells in order to assess their responsiveness to ACTH. Both transient and long-lasting components of an inward calcium curren t were identified which were similar to T and L-type Ca2+ currents. Wi th Ba2+ as the charge carrier, the transient current activated at volt ages more hyperpolarized than -50 mV with V-1/2 for activation at -78. 1 mV, and for steady state inactivation at -52.3 mV. The L-type curren t activated at -20 mV, with a V-1/2 for activation at -29.9 mV and ste ady state inactivation at -44.2 mV. Under perforated patch conditions the response was shifted to more depolarized voltages. Both currents w ere responsive to agents which usually affect T- or L-type Ca2+ curren ts. The transient current was completely blocked by 50 mu M lanthanum or 200 mu M nickel and partially blocked by 300 mM amiloride. Cadmium (100 mu M) and nifedipine (300 nM) completely blocked the long-lasting current while omega-conotoxin GVIA (192 nM) inhibited the current by only 20-25%. The agonist, Bay K 8644 was stimulatory at 50 nM. Both tr ansient and sustained outward potassium currents similar to A-type and delayed rectifier currents, respectively, were present. The transient current demonstrated fast activation at voltages more positive than - 10 mV, inactivation with continued depolarization and steady state ina ctivation at V-1/2 = -50 mV The sustained current activated rapidly an d had minimal inactivation with continued depolarization. The transien t current was blocked by 5 mM 4AP and the sustained by 25 mM TEA. Whil e Y-1 cells contain both calcium and potassium currents similar to tho se found in other adrenocortical cells, none of the currents were affe cted by ACTH or AII, secretagogues which stimulate steroidogenesis. Th ese data, combined with the inability of both Ca2+ and K+ channel bloc kers to alter ACTH-induced steroidogenesis as reported earlier, sugges ts that neither calcium nor potassium currents are responsive to ACTH in Y-1 cells.