Protection of excitotoxic neuronal death by gluconate through blockade of N-methyl-D-aspartate receptors.
Excitotoxic neuronal death is mediated primarily by the N-methyl-D-aspartate receptor. N-methyl-D-aspartate induces two forms of excitotoxicity in CA1 pyramidal neurons of cultured rat hippocampal slices: the rapidly developing form that depends on external Na+ and Cl-, and the delayed form that requires external Ca2+ but not Cl-. Consistent with this notion, replacement of external Cl- with glucuronate, isethionate or methylsulfate attenuated or delayed selectively the rapid excitotoxicity. However, gluconate substituting for Cl- blocked both rapid and delayed forms of excitotoxicity. Gluconate also reduced N-methyl-D-aspartate-induced membrane currents recorded from CA1 neurons in a dose-dependent manner. This dose-dependence was remarkably similar to that observed for protection of N-methyl-D-aspartate-induced neuronal death by gluconate. Although gluconate chelated Ca2+ most strongly among the four Cl- substitutes examined, excitotoxic neuronal death could be protected by 7 mM gluconate without Ca2+ chelating action. The voltage-dependent Mg2+ block of N-methyl-D-aspartate receptors was not affected by gluconate. Gluconate suppressed the N-methyl-D-aspartate component of excitatory synaptic currents evoked in CA1 neurons. We conclude that protection of excitotoxic neuronal death by gluconate at low doses (<20 mM) is due to its antagonistic action on N-methyl-D-aspartate receptors. Gluconate is a widely used substitute for Cl-. Our unexpected findings give a warning that the results of any of the experiments concerning excitotoxicity or glutamate receptors obtained by gluconate substituting for Cl- must be interpreted with caution.
Shionogi Research Laboratories, Futabacho, Toyonaka, Osaka, Japan.
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T
Sakaguchi
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Kuno
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K
Kawasaki
D000818:Animals; D002118:Calcium / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects*; D002478:Cells, Cultured; D004396:Coloring Agents; D019706:Excitatory Postsynaptic Potentials / Q000187:drug effects*; D005942:Gluconates / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects / Q000502:physiology; D018696:Neuroprotective Agents / Q000494:pharmacology*; D011419:Propidium; D051381:Rats; D017207:Rats, Sprague-Dawley; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000502:physiology
D004396:Coloring Agents; D005942:Gluconates; D018696:Neuroprotective Agents; D016194:Receptors, N-Methyl-D-Aspartate; D011419:Propidium; C030691:gluconic acid; D002118:Calcium