RAB3-PEPTIDE STIMULATES EXOCYTOSIS FROM MAST-CELLS VIA A PERTUSSIS-TOXIN-SENSITIVE MECHANISM

Synthetic peptides of the putative effector domain of members of the r ab3 gene family of small GTP-binding proteins have been shown to have potent actions on vesicular transport and exocytosis [1,2]. Here, we u se similar rab3-effector domain peptides to study their role in intrac ellular signalling in mast cells. We find that rab3-like peptides stim ulate exocytosis and decrease cyclic 3',5'-AMP levels in these cells w hen applied extracellularly. Cells pretreated with pertussis toxin (Pt X) to selectively uncouple alpha(i)/alpha(o) type G proteins from thei r biological activators, however, did not respond to rab3 peptides. ra b3-like peptides also induce a Ca2+ transient in mast cells. These obs ervations provide evidence for functional coupling between an effector domain peptide sequence of rab3 protein and a PtX-sensitive G protein substrate.