L-type Ca(2+) channel-mediated Zn(2+) toxicity and modulation by ZnT-1 in PC12 cells

In view of evidence that Zn(2+) neurotoxicity contributes to some forms of pathological neuronal death, we developed a model of Zn(2+) neurotoxicity in a cell line amenable to genetic manipulations. Exposure to 500 microM ZnCl(2) for 15 min under depolarizing conditions resulted in modest levels of PC12 cell death, that was reduced by the L-type Ca(2+) channel antagonist, nimodipine, and increased by the L-type Ca(2+) channel opener, S(-)-Bay K 8644. At lower insult levels (200 micrometer Zn(2+)+Bay K 8644), Zn(2+)-induced death appeared apoptotic under electron microscopy and was sensitive to the caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-CH(2)F (Z-VAD); at higher insult levels (1000 microM+Bay K 8644), cells underwent necrosis insensitive to Z-VAD. To test the hypothesis that the plasma membrane transporter, ZnT-1, modulates Zn(2+) neurotoxicity, we generated stable PC12 cell lines overexpressing wild type or dominant negative forms of rat ZnT-1 (rZnT-1). Clones T9 and T23 overexpressing wild type rZnT-1 exhibited enhanced Zn(2+) efflux and reduced vulnerability to Zn(2+)-induced death compared to the parental line, whereas clones D5 and D16 expressing dominant negative rZnT-1 exhibited the opposite characteristics.