Adrenocorticotropin Activates Barium-Conducting Channels from Bovine Adrenocortical Zona Fasciculata Cells in Lipid Bilayers*

Abstract

Plasma membranes from bovine adrenal zona fasciculata cells were incorporated into lipid bilayers, and the activity of individual calcium channels was monitored under voltage clamp conditions. Using barium as the permeant ion, two distinct channels with conductances of approximately 8 and 20 picoSiemens (pS) were characterized. The 20 pS conductance corresponds to conductances found in L-type calcium channels. This channel displayed voltage dependency and a sensitivity to BayK 8644. Addition of ACTH (10 nM) to the bilayer preparations promoted an increased open time for the 20-pS channel. These data confirm the presence of dihydropyridine-sensitive calcium channels in bovine adrenocortical cells and support a potential role for these channels as a site of modulation by ACTH.