Much of our current evidence concerning of the role of calcium (

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BackgroundChanges in ionic concentration have a fundamental effect on numerous physiological processes. For example, IP3-gated thapsigargin sensitive intracellular calcium (Ca2+) storage provides a source of the ion for many cellular signaling events. Less is known about the dynamics of other intracellular ions. The present study investigated the intracellular source of zinc (Zn2+) that has been reported to play a role in cell signaling.ResultsIn primary cultured cortical cells (neurons) labeled with intracellular fluorescent Zn2+ indicators, we showed that intracellular regions of Zn2+ staining co-localized with the endoplasmic reticulum (ER). The latter was identified with ER-tracker Red, a marker for ER. The colocalization was abolished upon exposure to the Zn2+ chelator TPEN, indicating that the local Zn2+ fluorescence represented free Zn2+ localized to the ER in the basal condition. Blockade of the ER Ca2+ pump by thapsigargin produced a steady increase of intracellular Zn2+. Furthermore, we determined that the thapsigargin-induced Zn2+ increase was not dependent on extracellular Ca2+ or extracellular Zn2+, suggesting that it was of intracellular origin. The applications of caged IP3 or IP3-3Kinase inhibitor (to increase available IP3) produced a significant increase in intracellular Zn2+.ConclusionsTaken together, these results suggest that Zn2+ is sequestered into thapsigargin/IP3-sensitive stores and is released upon agonist stimulation.

There is a rising intracellular Zn 2 + transient during neuronal ischemic hypoxia (oxygen-glucose deprivation and reoxygenation, OGD/R). The results of our recent works suggest that the OGD/ R-induced Zn 2 + transient can readily be mistaken for a Ca 2 + transient. The aim of this study was to examine the respective functions of Zn 2 + and Ca 2 + in OGD/R-induced neuronal injury. We showed that [Zn 2 + ] i accumulation was consistently met with the induction of OGD/R-induced cell injury. Ca 2 + accumulation induced with high [K + ] (to open voltage-gated calcium channels) or ionomycin (a Ca 2 + ionophore) caused a moderate neuronal injury that was reduced significantly by the application of the Zn 2 + chelator N,N,N 0 ,N 0 -tetrakis(2-pyridylmethyl)ethylenediamine (TPEN). In comparison, Zn 2 + accumulation, induced with the Zn 2 + ionophore pyrithione, resulted in significantly greater injury. The application of nimodipine and MK801 was shown to attenuate neuronal injury only from a mild (10 mins) OGD insult. Neuronal injury from more severe (30 mins) OGD was not mitigated by the ion channel antagonists, whereas treatment with the Zn 2 + chelator TPEN did afford significant protection from cell injury. These results indicate Zn 2 + -mediated damage to be of greater consequence than Ca 2 + -mediated damage, and collectively support the suggestion that Zn 2 + accumulation may be a more significant causal factor of OGD/R-induced neuronal injury.

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