Ethanol induces glutamate secretion by Ca2+ mobilization and ROS generation in rat hippocampal astrocytes

In this study we have investigated the effect of ethanol on [Ca2+]c by microfluorimetry and glutamate secretion using an enzyme-linked system, in rat hippocampal astrocytes in culture. Our results show that ethanol (1-200 mM) evoked a dose-dependent increase in glutamate secretion. 50 mM ethanol, a concentration within the range of blood alcohol levels in intoxicated humans, induced a release of Ca2+ from intracellular stores in the form of oscillations. Ca2+-mobilizing effect of ethanol was not prevented by preincubation of cells in the presence of 2 mM of the antioxidant dithiothreitol. Ethanol-evoked glutamate secretion was reduced when extracellular Ca2+ was omitted (medium containing 0.5 mM EGTA) and following preincubation of astrocytes in the presence of the intracellular Ca2+ chelator 1,2-bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid tetraacetoxy-methyl ester (10 microM). Preincubation of astrocytes in the presence of 2 mM of the antioxidant dithiothreitol significantly reduced ethanol-evoked glutamate secretion. Finally, preincubation of astrocytes in the presence of bafilomycin (50 nM) significantly reduced ethanol-induced neurotransmitter release, indicating that exocytosis is involved in glutamate secretion. In conclusion, our results suggest that ethanol mobilizes Ca2+ from intracellular stores, and stimulates a Ca2+-dependent glutamate secretion, probably involving reactive oxygen species production, and therefore creating a situation potentially leading to neurotoxicity in the hippocampus.