Potassium channels are involved in zinc-induced apoptosis in MES23.5 cells

There is evidence that zinc may be involved in the pathogenesis of Parkinson's disease by an apoptotic pathway. However, the mechanisms underlying zinc-induced apoptosis are unknown. Previous studies showed that 6-hydroxydopamine (6-OHDA)-enhanced potassium channels are involved in apoptosis of dopaminergic neurons. Our study was designed to test whether zinc-induced apoptosis was mediated by potassium channels. First we demonstrated cell apoptosis with zinc treatment by Hoechst staining assay. The results showed that 13.38% +/- 0.6% of MES23.5 cells were apoptotic after 24 hr of incubation with 60 microM zinc sulfate. Then we observed that the tyrosine hydroxylase (TH) protein expression and the dopamine content decreased, as detected by Western blots and high-performance liquid chromatography-electrochemical detection (HPLC-ECD). We further elucidated the mechanism of cell apoptosis by using whole-cell patch clamp recording. The data demonstrated that MES23.5 cells exhibited a tetraethylammonium (TEA)-sensitive outward K(+) current with delayed rectifier characteristics. Increases of K(+) current density were recorded following the treatment with 60 microM zinc for 4-8 hr. After incubation with 20 mM TEA, the zinc-induced enhancement of K(+) currents was fully blocked. Furthermore, incubation with TEA blocked zinc-mediated caspase-3 activation and cell apoptosis. These data suggest that zinc-induced apoptosis of MES23.5 dopaminergic cells may due to the enhancement of TEA-sensitive K(+) channel activity.