Pancreastatin receptor is coupled to a guanosine triphosphate–binding protein of the G g/11 α 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 G q/11 α by different approaches. Indirect evidence of a pertussis toxin (PT)‐insensitive G protein of the family of G q/11 α 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‐G q/11 α 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 G q/11 α was found to be associated with the semipurified PST receptor. Moreover, anti‐G q/11 α antisera immunoprecipitated most PST‐binding activity (95%), bringing down most of the specific G protein, whereas anti‐G i1,2 α and ‐G o,i3 α failed to immunoprecipitate the PST‐binding activity. Finally, the coupling of the PST receptor with the effector phospholipase C was disrupted by blocking with G q/11 α antisera, suggesting that a G protein of the family of G q/11 α is a signal mediator from PST receptors to phospholipase C activation in rat liver membranes.