title: Elevated endogenous nitric oxide increases Ca2+ flux via L-type Ca2+ channels by S-nitrosylation in rat hippocampal neurons during severe hypoxia and in vitro ischemia.
abstract: Nitric oxide (NO) mediates pathogenic changes in the brain subsequent to energy deprivation; yet the NO mechanism involved in the early events remains unclear. We examined the acute effects of severe hypoxia and oxygen-glucose deprivation (OGD) on the endogenous NO production and the NO-mediated pathways involved in the intracellular calcium ([Ca(2+)](i)) response in the rat hippocampal neurons. The levels of NO and [Ca(2+)](i) in the CA1 region of the slices rapidly elevated in hypoxia and were more prominent in OGD, measured by the electrochemical method and spectrofluorometry, respectively. The NO and [Ca(2+)](i) responses were enhanced by L-arginine and were reduced by NO synthase inhibitors, suggesting that the endogenous NO increases the [Ca(2+)](i) response to energy deprivation. Nickel and nifedipine significantly decreased the NO and [Ca(2+)](i) responses to hypoxia and OGD, indicating an involvement of L-type Ca(2+) channels in the NO-mediated mechanisms. In addition, the [Ca(2+)](i) responses were attenuated by ODQ or KT5823, inhibitors of the cGMP-PKG pathway, and by acivicin, an inhibitor of gamma-glutamyl transpeptidase for S-nitrosylation, and by the thiol-alkylating agent N-ethylmaleimide (NEM). Moreover, L-type Ca(2+) currents in cultured hippocampal neurons with whole-cell recording were significantly increased by L-arginine and were decreased by L-NAME. Pretreatment with NO synthase inhibitors or NEM but not ODQ abolished the effect of L-arginine on the Ca(2+) currents. Also, vitamin C, which decomposes nitrosothiol but not disulfide by reduction, reversed the change in the Ca(2+) current with L-arginine. Taken together, the results suggest that an elevated endogenous NO production enhances the influx of Ca(2+) via the hippocampal L-type Ca(2+) channel by S-nitrosylation during an initial phase of energy deprivation.
authors.affiliation: Department of Physiology, University of Hong Kong, Faculty of Medicine Building, 21 Sassoon Road, Pokfulam, Hong Kong.
authors.forename: Yung-Wui
authors.initials: YW
authors.lastname: Tjong
authors.forename: Kuihuan
authors.initials: K
authors.lastname: Jian
authors.forename: Meifang
authors.initials: M
authors.lastname: Li
authors.forename: Ming
authors.initials: M
authors.lastname: Chen
authors.forename: Tian-Ming
authors.initials: TM
authors.lastname: Gao
authors.forename: Man-Lung
authors.initials: ML
authors.lastname: Fung
mesh_terms: D000818:Animals; D001120:Arginine / Q000494:pharmacology; D002545:Brain Ischemia / Q000378:metabolism* / Q000473:pathology; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000378:metabolism*; D015687:Cell Hypoxia; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000378:metabolism; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016257:Fura-2; D006624:Hippocampus / Q000166:cytology / Q000378:metabolism*; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D009569:Nitric Oxide / Q000494:pharmacology*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D026403:S-Nitrosothiols / Q000378:metabolism
chemical_list: D020746:Calcium Channels, L-Type; D004791:Enzyme Inhibitors; D026403:S-Nitrosothiols; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D006152:Cyclic GMP; D010100:Oxygen; D002118:Calcium; D016257:Fura-2; D019331:NG-Nitroarginine Methyl Ester