GABAAand GABABreceptors are functionally active in the regulation of catecholamine secretion by bovine chromaffin cells

Abstract

GABA stimulates the basal catecholamine release from adrenal bovine chromaffin cells in a calciumdependent manner. This release represents about 70% of that obtained by similar doses of nicotine under similar experimental conditions. This effect is mediated by GABA_A receptor sites present in chromaffin cells, since it was mimicked by muscimol and reversed by bicuculline. In addition, GABA, through its GABA_A receptors, increases the catecholamine release evoked by submaximal doses of aicotine, but it has no effect on nicotine‐evoked secretion of catecholamines when nicotine was given at maximal doses. These results seem to indicate that both nicotine and GABA release catecholamines from the same intracellular pool. In contrast, baclofen, a GABA_B receptor agonist, depressed both basal and nicotineevoked catecholamine release; this result indicates that in addition to GABA_A control of catecholamine secretion by chromaffin cells, there is a GABA_B control of this function. These results support the existence of a dual regulation of catecholamine secretion by both the GABA_A and GABA_B receptors in a similar way as that proposed for muscarinic and nicotinic cholinergic receptors.