Extracellular accumulation of glutamate in the hippocampus induced by ischemia is not calcium dependent — In vitro and in vivo evidence

Calcium dependency of ischemia-induced increase in extracellular glutamate in the hippocampus was studied in vitro and in vivo. Perfusion of a low pO 2 medium without glucose (in vitro ischemia) induced an increase in extracellular glutamate in rat hippocampal slices. This increase did not depend on Ca 2+. which is in contrast with the observation that about 40% of membrane depolarization (50 mM KCl)-evoked release was Ca 2+-dependent. In vivo cerebral ischemia of 5 min duration in gerbils also caused Ca 2+-independent increase in extracellular glutamate in the hippocampus. The data suggest that the increase in extracellular glutamate induced by ischemia is not due to the enhanced release of neurotransmitter glutamate.