Na(+) and Ca(2+) homeostasis pathways, cell death and protection after oxygen-glucose-deprivation in organotypic hippocampal slice cultures.

Intracellular ATP supply and ion homeostasis determine neuronal survival and degeneration after ischemic stroke. The present study provides a systematic investigation in organotypic hippocampal slice cultures of the influence of experimental ischemia, induced by oxygen-glucose-deprivation (OGD). The pathways controlling intracellular Na(+) and Ca(2+) concentration (Na(+) and Ca(2+)) and their inhibition were correlated with delayed cell death or protection. OGD induced a marked decrease in the ATP level and a transient elevation of Ca(2+) and Na(+) in cell soma of pyramidal neurons. ATP level, Na(+) and Ca(2+) rapidly recovered after reintroduction of oxygen and glucose. Pharmacological analysis showed that the OGD-induced Ca(2+) elevation in neuronal cell soma resulted from activation of both N-methyl-d-aspartate (NMDA)-glutamate receptors and Na(+)/Ca(2+) exchangers, while the abnormal Na(+) elevation during OGD was due to Na(+) influx through voltage-dependent Na(+) channels. In hippocampal slices, cellular degeneration occurring 24 h after OGD, selectively affected the pyramidal cell population through apoptotic and non-apoptotic cell death. OGD-induced cell loss was mediated by activation of ionotropic glutamate receptors, voltage-dependent Na(+) channels, and both plasma membrane and mitochondrial Na(+)/Ca(2+) exchangers. Thus, we show that neuroprotection induced by blockade of NMDA receptors and plasma membrane Na(+)/Ca(2+) exchangers is mediated by reduction of Ca(2+) entry into neuronal soma, whereas neuroprotection induced by blockade of AMPA/kainate receptors and mitochondrial Na(+)/Ca(2+) exchangers might result from reduced Na(+) entry at dendrites level.