GABAA receptor-mediated increase of cytosolic Ca2+ in isolated bovine adrenal chromaffin cells.

We have studied the effects of GABA on cytosolic free Ca2+ concentration ([Ca2+]i) as a means of investigating the role of GABA in adrenal catecholamine (CA) secretion. It was demonstrated that GABA caused an elevation of [Ca2+]i via the GABAA receptor in a concentration-dependent manner, which was well correlated with an increase of 45Ca uptake, an increase of CA release and a depolarization of chromaffin cells assessed with bis-oxonol fluorescence. Since the GABA-induced rise of [Ca2+]i was absolutely dependent on the presence of extracellular Ca2+ and partly sensitive to nifedipine, at least one entry route for Ca2+ facilitated by GABA via a voltage-sensitive Ca2+ channel was suggested. When extracellular Cl- was lowered, GABA-induced CA release, depolarization, and rise of [Ca2+]i were all markedly enhanced. It is possible that GABA plays a modulatory role in the regulation of adrenal CA secretion as a facilitatory modulator.