Inhibition of different pathways influencing Na+ homeostasis protects organotypic hippocampal slice cultures from hypoxic/hypoglycemic injury

A prominent feature of cerebral ischemia is the excessive intracellular accumulation of both Na+ and Ca2+, which results in subsequent cell death. A large number of studies have focused on pathways involved in the increase of the intracellular Ca2+ concentration [Ca2+](i), whereas the elevation of intracellular Na+ has received less attention. In the present study we investigated the effects of inhibitors of different Na+ channels and of the Na+/Ca2+ exchanger, which couples the Na+ to the Ca2+ gradient, on ischemic damage in organotypic hippocampal slice cultures. The synaptically evoked population spike in the CA1 region was taken as a functional measure of neuronal integrity. Neuronal cell death was assessed by propidium iodide staining. The Na+ channel blocker tetrodotoxin, and the NMDA receptor blocker MK 801, but not the AMPA/kainate receptor blocker NBQX prevented ischemic cell death. The novel Na+/Ca2+ exchange inhibitor 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea methanesulfonate (KB-R7943), which preferentially acts on the reverse mode of the exchanger, leading to Ca2+ accumulation, also reduced neuronal damage. At higher concentrations, KB-R7943 also inhibits Ca2+ extrusion by the forward mode of the exchanger and exaggerates neuronal cell death. Neuroprotection by KB-R7943 may be due to reducing the [Ca2+](i) increase caused by the exchanger. (C) 2000 Elsevier Science Ltd. All rights reserved.