Pancreastatin receptor is coupled to a guanosine triphosphate-binding protein of the Gg/11α family in rat liver membranes

Pancreastatin (PST), a recently discovered regulatory peptide derived from chromogranin A, has been shown to have a glycogenolytic effect in the hepatocyte that is mediated by increasing intracellular calcium. Our previous studies on pancreastatin signaling suggested that PST receptor is coupled to some G proteins in the plasma membrane of the hepatocyte. The nature of this interaction was investigated using antisera against Gq/11α by different approaches. Indirect evidence of a pertussis toxin (PT)-insensitive G protein of the family of Gq/11α was obtained by measuring high-affinity guanosine triphosphatase (GTPase) activity in soluble rat liver membranes. PST increased GTPase activity in a dose-dependent manner. This effect was only slightly inhibited by PT pretreatment of the membranes, whereas anti-Gq/11α antisera blocked most of the PST-stimulated GTPase activity. The selective association of the PST receptor with this G protein was further studied by the coelution in wheat germ agglutinin semipurification of the receptor and by immunoprecipitation of the G protein-PST receptor complexes using G-protein-specific antisera. A G protein of the family of Gq/11α was found to be associated with the semipurified PST receptor. Moreover, anti-Gq/11α antisera immunoprecipitated most PST-binding activity (95%), bringing down most of the specific G protein, whereas anti-Gi1,2α and -Go,i3α failed to immunoprecipitate the PST-binding activity. Finally, the coupling of the PST receptor with the effector phospholipase C was disrupted by blocking with Gq/11α antisera, suggesting that a G protein of the family of Gq/11α is a signal mediator from PST receptors to phospholipase C activation in rat liver membranes.