Regulation of thrombin-induced mast cell degranulation by zinc and manganese

This study was undertaken to determine whether zinc, manganese and copper could regulate the thrombin-induced secretion of the granule-associated mediator, β-hexosaminidase, from mast cells derived from mouse bone marrow. Exposure of thrombin to copper (2-100 μM) does not affect the enzyme-induced release of β-hexosaminidase from the mast cells. Zinc at 50 μM reduced the degranulation of calcium ionophore A23187 activated cells by 75% and that of immunological challenge or thrombin by 30% each. Exposure of the thrombin to incremental concentrations of manganese (2-100 μM) prevents its degranulation activity in a dose-related fashion. 75% inhibition of the enzyme activity was achieved at 100 μM manganese. However, exposure of IgE sensitized or unsensitized cells to incremental concentrations of manganese (2-400 μM) prior to antigen or calcium ionophore A23187 stimulation, does not significantly affect the exocytosis of β-hexosaminidase. The binding of purified human FITC-thrombin to E-mast cells was analyzed by fluorescence flow cytometry. All cells bound specifically the labelled thrombin. Pretreatment of the FITC-thrombin with 100 μm zinc or manganese had no effect on the binding of the labelled thrombin to the cells. It was assumed that manganese modulates either directly the thrombin activity or the substrate for the enzyme on the cell surface.