Mild acidosis enhances AMPA receptor-mediated intracellular zinc mobilization in cortical neurons.
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+.
Frazzini
Valerio
V
Department of Basic and Applied Medical Science, Molecular Neurology Unit, CeSI-Center for Excellence on Aging, University G. d'Annunzio, Chieti, Italy.
Rapposelli
Ilario G
IG
Corona
Carlo
C
Rockabrand
Erica
E
Canzoniero
Lorella M T
LM
Sensi
Stefano L
SL
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*
D018091:Receptors, AMPA; D015032:Zinc; D007608:Kainic Acid