title: Mild acidosis enhances AMPA receptor-mediated intracellular zinc mobilization in cortical neurons.
abstract: Overactivation of glutamate receptors and subsequent deregulation of the intraneuronal calcium ([Ca2+]i) levels are critical components of the injurious pathways initiated by cerebral ischemia. Another hallmark of stroke is parenchymal acidosis, and we have previously shown that mild acidosis can act as a switch to decrease NMDAR-dependent neuronal loss while potentiating the neuronal loss mediated by AMPARs. Potentiation of AMPAR-mediated neuronal death in an acidotic environment was originally associated only with [Ca2+]i dyshomeostasis, as assessed by Ca2+ imaging; however, intracellular dyshomeostasis of another divalent cation, Zn2+, has recently emerged as another important co-factor in ischemic neuronal injury. Rises in [Zn2+]i greatly contribute to the fluorescent changes of Ca2+-sensitive fluorescent probes, which also have great affinity for Zn2+. We therefore revisited our original findings (Mcdonald et al., 1998) and investigated if AMPAR-mediated fura-2 signals we observed could also be partially due to [Zn2+]i increases. Fura-2 loaded neuronal cultures were exposed to the AMPAR agonist, kainate, in a physiological buffer at pH 7.4 and then washed either at pH 7.4 or pH 6.2. A delayed recovery of fura-2 signals was observed at both pHs. Interestingly this impaired recovery phase was found to be sensitive to chelation of intracellular Zn2+. Experiments with the Zn2+ sensitive (and Ca2+-insensitive) fluorescent probe FluoZin-3 confirmed the idea that AMPAR activation increases [Zn2+]i, a phenomenon that is potentiated by mild acidosis. Additionally, our results show that selective Ca2+ imaging mandates the use of intracellular heavy metal chelators to avoid confounding effects of endogenous metals such as Zn2+.
authors.affiliation: Department of Basic and Applied Medical Science, Molecular Neurology Unit, CeSI-Center for Excellence on Aging, University G. d'Annunzio, Chieti, Italy.
authors.forename: Valerio
authors.initials: V
authors.lastname: Frazzini
authors.forename: Ilario G
authors.initials: IG
authors.lastname: Rapposelli
authors.forename: Carlo
authors.initials: C
authors.lastname: Corona
authors.forename: Erica
authors.initials: E
authors.lastname: Rockabrand
authors.forename: Lorella M T
authors.initials: LM
authors.lastname: Canzoniero
authors.forename: Stefano L
authors.initials: SL
authors.lastname: Sensi
mesh_terms: D000138:Acidosis / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism*; D007608:Kainic Acid / Q000494:pharmacology; D051379:Mice; D009474:Neurons / Q000378:metabolism*; D018091:Receptors, AMPA / Q000819:agonists / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism*
chemical_list: D018091:Receptors, AMPA; D015032:Zinc; D007608:Kainic Acid