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.
Takahashi
M
M
Tsukuba Research Laboratories, Upjohn Pharmaceuticals Ltd., Ibaraki, Japan.
Hashimoto
M
M
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