ACTH-induced Cl− current in bovine adrenocortical cells: correlation with cortisol secretion

Abstract

ACTH has been shown to depolarize bovine adrenal zona fasciculata cells by inhibiting a K+ current. The effects of this hormone on such cells have been reexamined using perforated and standard patch recording methods. In current clamp experiments, ACTH (10 nM) induced a membrane depolarization to −36 ± 1 mV ( n = 56), which was mimicked by forskolin (10 μM) or by 8-(4-chlorophenylthio)-cAMP (8 mM). ACTH-induced membrane depolarizations were associated in the majority of cells with an increase in membrane conductance. In the other cells, these membrane responses could occur without change or could be correlated with a transient or with a continuous Cs+-sensitive decrease in membrane conductance. The depolarizations associated with an increase in membrane conductance were depressed by Cl− current inhibitors diphenylamine-2-carboxylic acid (DPC; 1 mM), anthracene-9-carboxylic acid (9-AC; 1 mM), DIDS (400 μM), verapamil (100 μM), and glibenclamide (20 μM). In voltage-clamped Cs+-loaded cells, ACTH activated a time-independent current that displayed an outward rectification and reversed at −21.5 mV ± 2 ( n = 6). This current, observed in the presence of internal EGTA (5 mM), was depressed in low Cl− external solution and was inhibited by DPC, 9-AC, DIDS, 5-nitro-2-(3-phenylpropylamino)benzoic acid, verapamil, and glibenclamide. ACTH-stimulated cortisol secretion was blocked by Cl− channel inhibitors DIDS (400 μM) and DPC (1 mM). The present results reveal that, in addition to inhibiting a K+current, ACTH activates in bovine zona fasciculata cells a Ca2+-insensitive, cAMP-dependent Cl− current. This Cl− current is involved in the ACTH-induced membrane depolarization, which seems to be a crucial step in stimulating steroidogenesis.