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 acc umulation of both Na+ and Ca2+, which results in subsequent cell death. A l arge number of studies have focused on pathways involved in the increase of the intracellular Ca2+ concentration [Ca2+](i), whereas the elevation of i ntracellular Na+ has received less attention. In the present study we inves tigated the effects of inhibitors of different Na+ channels and of the Na+/ Ca2+ exchanger, which couples the Na+ to the Ca2+ gradient, on ischemic dam age in organotypic hippocampal slice cultures. The synaptically evoked popu lation spike in the CA1 region was taken as a functional measure of neurona l 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 de ath. The novel Na+/Ca2+ exchange inhibitor 2-[2-[4-(4-nitrobenzyloxy)phenyl ]ethyl]isothiourea methanesulfonate (KB-R7943), which preferentially acts o n the reverse mode of the exchanger, leading to Ca2+ accumulation, also red uced neuronal damage. At higher concentrations, KB-R7943 also inhibits Ca2 extrusion by the forward mode of the exchanger and exaggerates neuronal ce ll 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.