Release of D-[3H]aspartate and [14C]GABA in rat hippocampus slices: effects of fatty acid-free bovine serum albumin and Ca2+ withdrawal.

Extended incubation of hippocampus slices in the presence of fatty acid-free bovine serum albumin (FAF-BSA) strongly enhanced the release of D-[3H]aspartate and [14C]GABA induced by veratridine. Saturation of the FAF-BSA with oleic acid abolished the enhancing effect. Spontaneous release and K+-induced release were not significantly changed by the addition of FAF-BSA. Amino-oxyacetic acid in the medium enhanced the veratridine-induced release of D-[3H] aspartate. The spontaneous release of [14C]GABA was greatly increased by Ca2+ withdrawal. With the further addition of EGTA the spontaneous release in the absence of Ca2+ increased more than 8-fold over the measured in the presence of 1.5 mM Ca2+. The enhanced release caused by Ca2+ withdrawal was totally blocked by tetrodotoxin. The toxin was effective even when added after the spontaneous release in the absence of Ca2+ was already proceeding at a high rate. The veratridine-induced release of [14C]GABA was also considerably augmented by Ca2+ withdrawal. D-[3H]aspartate release, studied simultaneously with [14C]GABA by double labeling, did not show enhanced spontaneous release upon Ca2+ withdrawal. The findings provide evidence that the enhanced [14C]GABA release caused by Ca2+ withdrawal is mediated by voltage-dependent Na+ channels.