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.