Zinc influx and physiological consequences in the β-insulinoma cell line, Min6

In the mammalian pancreas, high concentrations of Zn2+ are co-secreted with insulin, which may then permeate via abundant L-type Ca2+ channels (LTCC) present on the β-cells. Neither the mechanisms utilized by these cells to lower cytosolic Zn2+ nor the implications of increased intracellular Zn2+ on β-cell survival are well understood. To address this, we employed cell imaging of Zn2+ and Ca2+ in the β-insulinoma cell line, Min6. Depolarization induced an intense zinc influx that was blocked by nifedipine and verapamil, indicating that Zn2+ permeates via the LTCC. Both Ca2+ and Zn2+ permeated concomitantly, yet while Ca2+ was subsequently removed from the cytosol, Zn2+ was retained in the cells. Fluorescent staining of vesicular Zn2+ using ZP1 demonstrated that Zn2+ could be slowly sequestered following a brief exposure to low concentration of Zn2+. In contrast, cells were unable to sequester Zn2+ following application of high concentrations, which was followed by massive cell death. Our results demonstrate homeostatic crosstalk between the plasma membrane and intracellular zinc transporters and suggest that attenuating zinc influx may enhance β-cell survival.