Early events in the activation of Ca2+ dependent secretion: studies with rat peritoneal mast cells.

1. Secretion of histamine from mast cells is a Ca2+ dependent exocytotic process initiated by attachment of various agents to receptors on the cell surface. Secretion can also be triggered by the Ca2+ ionophores A23187 and ionomycin. Only in the case of the ionophores is the mechanism of Ca2+ mobilisation understood. 2. When agonist ligands are added to cells which have been preincubated with 32P-phosphate or 3H-inositol, one can detect an increase in the rate of labeling of phosphatidylinositol. As for other systems, the phosphatidylinositol response in mast cells shows the characteristics of an early receptor directed event. 3. We discuss the relationship of the phosphatidylinositol response and Ca2+ mobilisation in mast cell activation.