BICARBONATE-SENSITIVE CYSTEINE INDUCED ELEVATION OF EXTRACELLULAR ASPARTATE AND GLUTAMATE IN RAT HIPPOCAMPUS IN-VITRO

The effect of different concentrations of cysteine (0.125, 0.25, 0.5 a nd 1 mM) on the net efflux of endogenous amino acids was studied by th e incubation of rat hippocampal slices. Addition of cysteine (1 mM) in bicarbonate containing low K+ medium (5 min) selectively increased th e basal net efflux of glutamate and aspartate by 370% and 396%, respec tively. High K+ media (50 mM) containing cysteine (1 mM) evoked the ne t efflux of glutamate and aspartate by 1454% and 1019%, respectively. The corresponding effects in control slices without cysteine were 669% and 404%, respectively. No changes were observed on the concentration s of GABA, glutamine and taurine. The cysteine oxidation products, cys teine sulfinate (0.5 mu M) and cystine (0.25 mM) were without effects. The effect of cysteine (0.5 mM) was dramatically reduced in media wit h no added bicarbonare/CO2. Thus, cysteine in a bicarbonate-sensitive manner selectively increases the extracellular concentration of excito toxic amino acids in adult rat brain in vitro, possibly by interfering with the carrier-mediated glutamate uptake/release. (C) 1997 Elsevier Science Ltd. All rights reserved.