A GTP analogue induces calcium release but not secretion in rat mast cells

Two G protein-mediated events, calcium release and secretion, were measured in single rat peritoneal mast cells using the patch-clamp technique. Various phosphorothioate analogues of GTP were introduced into the cells. While GTP gamma S and Rp-GTP alpha S activated both processes, Rp-GTP beta S was found to induce repetitive calcium release in the absence of exocytosis. This response was modulated by IP3, heparin, compound 48/80, and ATP. Our results suggest that Rp-GTP beta S simulates Gp, which links receptors to calcium release.