GABA activity in dispersed bovine pineal cells: effect on serotonin release and calcium and chloride uptake

The presence of gamma-aminobutyric acid (GABA) and peripheral and central benzodiazepine receptors in the mammalian pineal gland prompted the examination of GABAergic transmission in dispersed bovine pineal cells. The effect of GABA on 3H-serotonin (5HT) release was examined in bovine pineal cells. GABA, by acting through GABA B receptor subtype, decreased 5HT release and by acting through GABA B, and presumably through GABA A receptor subtypes, inhibited depolarization-induced 45Ca2+ uptake in bovine pinealocytes. GABA, by acting on GABA B as well as on GABA A receptors, prevented the 5HT2- or 5HT1C-mediated stimulatory effect of serotonergic agonists on calcium uptake in pineal cells. GABA augmented 36Cl- uptake by bovine pineal cells. These results are interpreted to indicate that, by regulating the release of 5HT, GABA may modulate the synthesis and action of melatonin.