title: Role of kainate receptor activation and desensitization on the [Ca(2+)](i) changes in cultured rat hippocampal neurons.
abstract: We investigated the role of kainate (KA) receptor activation and desensitization in inducing the increase in the intracellular free Ca(2+) concentration ([Ca(2+)](i)) in individual cultured rat hippocampal neurons. The rat hippocampal neurons in the cultures were shown to express kainate receptor subunits, KA2 and GluR6/7, either by immunocytochemistry or by immunoblot analysis. The effect of LY303070, an alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptor antagonist, on the alterations in the [Ca(2+)](i) caused by kainate showed cell-to-cell variability. The [Ca(2+)](i) increase caused by kainate was mostly mediated by the activation of AMPA receptors because LY303070 inhibited the response to kainate in a high percentage of neurons. The response to kainate was potentiated by concanavalin A (Con A), which inhibits kainate receptor desensitization, in 82.1% of the neurons, and this potentiation was not reversed by LY303070 in about 38% of the neurons. Also, upon stimulation of the cells with 4-methylglutamate (MGA), a selective kainate receptor agonist, in the presence of Con A, it was possible to observe [Ca(2+)](i) changes induced by kainate receptor activation, because LY303070 did not inhibit the response in all neurons analyzed. In toxicity studies, cultured rat hippocampal neurons were exposed to the drugs for 30 min, and the cell viability was evaluated at 24 hr using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The selective activation of kainate receptors with MGA, in the presence of Con A, induced a toxic effect, which was not prevented by LY303070, revealing a contribution of a small subpopulation of neurons expressing kainate receptors that independently mediate cytotoxicity. Taken together, these results indicate that cultured hippocampal neurons express not only AMPA receptors, but also kainate receptors, which can modulate the [Ca(2+)](i) and toxicity.
authors.affiliation: Center for Neuroscience of Coimbra, Department of Zoology, University of Coimbra, Coimbra, Portugal.
authors.forename: A P
authors.initials: AP
authors.lastname: Silva
authors.forename: J O
authors.initials: JO
authors.lastname: Malva
authors.forename: A F
authors.initials: AF
authors.lastname: Ambrósio
authors.forename: A J
authors.initials: AJ
authors.lastname: Salgado
authors.forename: A P
authors.initials: AP
authors.lastname: Carvalho
authors.forename: C M
authors.initials: CM
authors.lastname: Carvalho
mesh_terms: D000818:Animals; D001569:Benzodiazepines / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D002614:Chelating Agents / Q000493:pharmacokinetics; D003208:Concanavalin A / Q000493:pharmacokinetics; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D005333:Fetus; D016257:Fura-2 / Q000493:pharmacokinetics; D005971:Glutamates / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D007150:Immunohistochemistry; D007608:Kainic Acid / Q000494:pharmacology; D018613:Microscopy, Confocal; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D009498:Neurotoxins / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018091:Receptors, AMPA / Q000187:drug effects* / Q000378:metabolism; D018092:Kainic Acid Receptors / Q000187:drug effects* / Q000378:metabolism; D013778:Tetrazolium Salts; D013844:Thiazoles; D000097808:GluK3 Kainate Receptor
chemical_list: D001569:Benzodiazepines; D002118:Calcium; D002614:Chelating Agents; D003208:Concanavalin A; D018691:Excitatory Amino Acid Antagonists; D016257:Fura-2; D005971:Glutamates; D007608:Kainic Acid; D008869:Microtubule-Associated Proteins; D009498:Neurotoxins; D018091:Receptors, AMPA; D018092:Kainic Acid Receptors; D013778:Tetrazolium Salts; D013844:Thiazoles; D000097808:GluK3 Kainate Receptor; C046105:4-methylglutamic acid; C118651:GYKI 53784; C022616:thiazolyl blue