No role for zinc in the storage of histamine in rat peritoneal mast cells.

The histamine in the granules of mast cells has been proposed to be stored as a heparin-zinc-histamine complex. Due to its chelating action zinc should increase (double) the histamine binding capacity of heparin. We have determined the zinc content of isolated rat peritoneal mast cells to 2.4-4.1 nmol/10-6 cells and of their granules to 13.3-21.4 nmol/mg dry weight. The corresponding amounts of histamine were 150 and 680 nmol respectively. The zinc content found is far (20 times) too low to allow for an adequate binding of histamine in a heparin-zinc-histamine complex. In vitro the granules take up zinc in the same manner as they take up other cations and zinc competes with histamine for granule storage sites. Consequently, Hi-uptake is reduced and not enhanced in the presence of zinc in the suspension medium. In summary no evidence was found for a storage function of zinc in a heparin-zinc-histamine complex.