Lowering extracellular Na+ concentration causes NMDA receptor-mediated neuronal death in cultured rat hippocampal slices.
Reduction of the transmembrane Na+ gradient is expected to induce neurotoxic glutamate release via reversed uptake. We describe neuronal death induced by lowering extracellular Na+ concentration in cultured rat hippocampal slices. When slices were exposed to 3.6 mM Na+ for 30 min, almost all the neurons in the CA1 region were degenerated within 20-24 h. The marginal concentration of external Na+ for induction of neurotoxicity was 6.6 mM. N-methyl-D-aspartate (NMDA) receptor antagonists, MK-801 at 1-3 microM and (+/-)-CPP at 30 microM, significantly decreased these neurotoxic effects. A non-NMDA receptor antagonist, DNQX at 30-100 microM, had no protective effect against neurotoxicity. Removal of external Ca2+ completely eliminated neuronal death, but replacing external Cl- with SO4(2-) had no protective effect against neurotoxicity. A drastic 40-fold increase in glutamate release was produced by 30 min exposure to 3.6 mM Na+, and this release was partially independent of external Ca2+. These findings suggest that the low-Na(+)-induced neurotoxicity we observed is mediated by excessive release of glutamate via reversed uptake and subsequent Ca(2+)-influx through NMDA receptors. The model reported here may be useful for investigation of the mechanism of neuronal injury mediated by endogenous glutamate.
Tsukuba Research Laboratories, Upjohn Pharmaceuticals Ltd., Ibaraki, Japan.
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Takahashi
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Hashimoto
D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects; D002712:Chlorides / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism; D006624:Hippocampus / Q000166:cytology*; D009474:Neurons / Q000737:chemistry / Q000166:cytology* / Q000187:drug effects; D009498:Neurotoxins / Q000494:pharmacology; D009924:Organ Culture Techniques; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology*
D002712:Chlorides; D018691:Excitatory Amino Acid Antagonists; D009498:Neurotoxins; D011810:Quinoxalines; D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; C056723:FG 9041; D016291:Dizocilpine Maleate; D012964:Sodium; D002118:Calcium