Adenosine triphosphatase in non-secreting and secreting mast cells

A Ca++-Mg++ ATPase has been demonstrated in the plasma membrane of rat peritoneal mast cells. The enzyme is localized by electron microscopy on the outer surface of the membrane. This agrees with the biochemical findings. A Ca++-Mg++ activated ATPase has also been shown to be present in the granule membrane. The optimal pH of the plasma membrane enzyme is close to the optimal pH for the histamine release. All the 14 inhibitors of plasma membrane ATPase tested - which caused varying degrees of inhibition of the enzyme - also inhibited histamine release induced by antigen, compound 48/80 and the divalent ionophore A23187. The conclusion from the study with the inhibitors is that a mild inhibition of the enzyme is compatible with histamine release, but a pronounced inhibition of the enzyme is always associated with inhibition of histamine release. ATP in low concentrations potentiates the release.