title: Intracellular zinc elevation measured with a "calcium-specific" indicator during ischemia and reperfusion in rat hippocampus: a question on calcium overload.
abstract: Much of our current evidence concerning of the role of calcium (Ca2+) as a second messenger comes from its interaction with fluorescent probes; however, many Ca2+ probes also have a higher affinity for another divalent cation: zinc (Zn2+). In this study, using a selective Zn2+ probe (Newport Green), we investigated the accumulation of intracellular Zn2+ transients in acute rat hippocampal slices during ischemia, simulated by oxygen and glucose deprivation (OGD). Subsequent reperfusion with glucose-containing oxygenated medium resulted in an additional increase in intracellular Zn2+. Such observations compelled us to investigate the contribution of Zn2+ to the alleged intracellular Ca2+ overload occurring in ischemia and reperfusion. Using confocal fluorescent microscopy of Calcium Green-1, a widely used Ca2+ indicator, we detected increases in fluorescence intensity during OGD and reperfusion. However, application of a Zn2+ chelator, at the peak of the fluorescence elevation (interpreted as Ca2+ overload), resulted in a significant drop in intensity, suggesting that rising Zn2+ is the primary source of the increasing Calcium Green-1 fluorescence. Finally, staining with the cell viability indicator propidium iodide revealed that Zn2+ is responsible for the ischemic neuronal cell death, because Zn2+ chelation prevented cells from sustaining ischemic damage. Current cellular models of ischemic injury center on Ca2+-mediated excitotoxicity. Our results indicate that Zn2+ elevation contributes to conventionally recognized Ca2+ overload and also suggest that the role of Ca2+ in neurotoxicity described previously using Ca2+ probes may need to be re-examined to determine whether effect previously attributed to Ca2+ could, in part, be attributable to Zn2+.
authors.affiliation: Department of Biomedical Science, Program in Molecular and Cellular Biology, Ohio University, Athens, Ohio 45701, USA.
authors.forename: Christian J
authors.initials: CJ
authors.lastname: Stork
authors.forename: Yang V
authors.initials: YV
authors.lastname: Li
mesh_terms: D000818:Animals; D002118:Calcium / Q000032:analysis / Q000378:metabolism*; D016923:Cell Death / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology; D006624:Hippocampus / Q000737:chemistry / Q000378:metabolism*; D007424:Intracellular Fluid / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D015424:Reperfusion / Q000379:methods; D015032:Zinc / Q000032:analysis / Q000378:metabolism*
chemical_list: D015032:Zinc; D002118:Calcium