G-protein activation mediates prepulse facilitation of Ca2+ channel currents in bovine chromaffin cells

• Published in: The Journal of membrane biology Vol. 140; no. 1; p. 47
• Main Authors: Doupnik, C A, Pun, R Y
• Format: Journal Article
• Language: English
• Published: United States 01.05.1994
• Subjects: Adenosine Triphosphate - metabolism; Adrenal Medulla - drug effects; Adrenal Medulla - metabolism; Animals; Calcium Channels - drug effects; Calcium Channels - metabolism; Catecholamines - metabolism; Cattle; Cells, Cultured; Enkephalins - metabolism; GTP-Binding Proteins - metabolism; Guanosine 5'-O-(3-Thiotriphosphate) - pharmacology; Guanosine Diphosphate - analogs & derivatives; Guanosine Diphosphate - pharmacology; Membrane Potentials; Thionucleotides - pharmacology
• ISSN: 0022-2631
• DOI: 10.1007/bf00234485

The effects of G-protein activation were investigated on tonic, large depolarization-induced Ca2+ channel facilitation in cultured bovine adrenal chromaffin cells. Under whole-cell voltage clamp, activation of G proteins by intracellular dialysis with 200 microM GTP-gamma S did not significantly affect prepulse facilitation or whole-cell Ba2+ current (IBa) density. In contrast, inactivation of G proteins by intracellular GDP-beta S or pertussis toxin (PTX) pretreatment completely abolished or markedly attenuated facilitation of IBa, respectively. GDP-beta S dialysis resulted in nearly a threefold increase in peak IBa density, whereas PTX pretreatment resulted in a 50% increase. Our results indicate that under control recording conditions (200 microM intracellular GTP), G proteins are tonically activated and suppress high-voltage-activated (HVA) Ca2+ channels in a voltage-dependent and voltage-independent manner. Local superfusion of chromaffin cells with normal bath solution produced a rapid and reversible increase (approximately 50%) in IBa amplitudes that also abolished prepulse facilitation. Together, these results demonstrate that tonic facilitation of HVA Ca2+ channels in bovine chromaffin cells involves the voltage-dependent relief of a G-protein-mediated suppression, imposed by chromaffin cell secretory products that feedback and activate G-protein-coupled autoreceptors.