Abstract
We have studied the effects of GABA on cytosolic free Ca 2+ concentration ([Ca 2+] i) as a means of investigating the role of GABA in adrenal catecholamine (CA) secretion. It was demonstrated that GABA caused an elevation of [Ca 2+] i via the GABA A 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 [Ca 2+] i was absolutely dependent on the presence of extracellular Ca 2+ and partly sensitive to nifedipine, at least one entry route for Ca 2+ facilitated by GABA via a voltage-sensitive Ca 2+ channel was suggested. When extracellular Cl − was lowered, GABA-induced CA release, depolarization, and rise of [Ca 2+] 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.
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