ACTIVATION OF EXOCYTOSIS BY THE HETEROTRIMERIC-G PROTEIN-G(I3)

Secretagogues of rat peritoneal mast cells, such as mastoparan and com pound 48/80, induce mast cell exocytosis by activating directly the gu anosine triphosphate-binding proteins that are required for exocytosis . The introduction of a synthetic peptide that corresponds to the carb oxyl-terminal end sequence of Galpha(i3) into the cells specifically b locked this secretion. Similar results were obtained when antibodies t o this peptide were introduced. The Galpha(i3) was located in both the Golgi and the plasma membrane, but only the latter source of Galpha(i 3) appeared to be essential for secretion. These results indicate that Galpha(i3) functions to control regulated exocytosis in mast cells.