GLUTAMATE-INDUCED INTRACELLULAR CALCIUM CHANGES AND NEUROTOXICITY IN CORTICAL-NEURONS IN-VITRO - EFFECT OF CHEMICAL ISCHEMIA

To study the role of calcium in neuronal death during ischemia, we exa mined the characteristics of intracellular Ca2+ ([Ca2+](i)) changes in single rat forebrain neurons exposed for 5 min to glutamate (3 mu M 1 mu M glycine), NMDA (30 mu M + 1 mu M glycine), kainate (100 mu M) or high K+ (50 mM), under both normal and ischemic conditions. The par ameters of [Ca2+](i) change measured included peak [Ca2+](i) level, pl ateau [Ca2+](i) level, area under the [Ca2+](i) response curve and tim e taken by [Ca2+](i) to recover to 10% of the peak response. Under nor mal conditions, all the agonists studied produced similar [Ca2+](i) ch anges. Chemical ischemia simulated by application of 5 mM KCN in gluco se-free buffer had no effect on the basal level of [Ca2+](i), but sign ificantly enhanced and prolonged the [Ca2+](i) changes produced by all the agonists. However, in toxicity studies, chemical ischemia signifi cantly potentiated the toxicity of only glutamate and N-methyl-D-aspar tate. In correlation studies, all the neurons which died displayed an irreversible secondary [Ca2+](i) load prior to loss of viability. Thes e studies suggest that while Ca2+ entry may play a critical role in ne uronal death, the magnitude of initial [Ca2+](i) change does not predi ct the toxicity of an agonist in cortical neurons.