title: Glutamate-induced calcium increase mediates magnesium release from mitochondria in rat hippocampal neurons.
abstract: Excess administration of glutamate is known to induce Ca(2+) overload in neurons, which is the first step in excitotoxicity. Although some reports have suggested a role for Mg(2+) in the excitotoxicity, little is known about its actual contribution. To investigate the role of Mg(2+) in the excitotoxicity, we simultaneously measured intracellular Ca(2+) and Mg(2+), using fluorescent dyes, Fura red, a fluorescent Ca(2+) probe, and KMG-104, a highly selective fluorescent Mg(2+) probe developed by our group, respectively. Administration of 100 μM glutamate supplemented with 10 μM glycine to rat hippocampal neurons induced an increase in intracellular Mg(2+) concentration ([Mg(2+)](i)). Extracellular Mg(2+) was not required for this glutamate-induced increase in [Mg(2+)](i), and no increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) or [Mg(2+)](i) was observed in neurons in nominally Ca(2+)-free medium. Application of 5 μM carbonyl cyanide p-(trifluoromethoxy) phenylhydrazone (FCCP), an uncoupler of mitochondrial inner membrane potential, also elicited increases in [Ca(2+)](i) and [Mg(2+)](i). Subsequent administration of glutamate and glycine following FCCP treatment did not induce a further increase in [Mg(2+)](i) but did induce an additive increase in [Ca(2+)](i). Moreover, the glutamate-induced increase in [Mg(2+)](i) was observed only in mitochondria localized areas. These results support the idea that glutamate is able to induced Mg(2+) efflux from mitochondria to the cytosol. Furthermore, pretreatment with Ru360, an inhibitor of the mitochondrial Ca(2+) uniporter, prevented this [Mg(2+)](i) increase. These results indicate that glutamate-induced increases in [Mg(2+)](i) result from the Mg(2+) release from mitochondria and that Ca(2+) accumulation in the mitochondria is required for this Mg(2+) release.
authors.affiliation: Center for Biosciences and Informatics, School of Fundamental Science and Technology, Graduate School of Science and Technology, Keio University, Yokohama, Kanagawa, Japan.
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Shindo
authors.forename: Ai
authors.initials: A
authors.lastname: Fujimoto
authors.forename: Kohji
authors.initials: K
authors.lastname: Hotta
authors.forename: Koji
authors.initials: K
authors.lastname: Suzuki
authors.forename: Kotaro
authors.initials: K
authors.lastname: Oka
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D016923:Cell Death / Q000502:physiology; D002478:Cells, Cultured; D018698:Glutamic Acid / Q000502:physiology* / Q000633:toxicity; D006624:Hippocampus / Q000378:metabolism / Q000502:physiology*; D008274:Magnesium / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism* / Q000473:pathology; D009498:Neurotoxins / Q000378:metabolism / Q000633:toxicity; D051381:Rats; D017208:Rats, Wistar; D015854:Up-Regulation / Q000502:physiology
chemical_list: D009498:Neurotoxins; D018698:Glutamic Acid; D008274:Magnesium; D002118:Calcium