PANCREASTATIN RECEPTOR IS COUPLED TO A GUANOSINE TRIPHOSPHATE-BINDINGPROTEIN OF THE G(Q 11)ALPHA 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 rec eptor is coupled to some G proteins in the plasma membrane of the hepa tocyte. The nature of this interaction was investigated using antisera against G(q/11)alpha by different approaches. Indirect evidence of a pertussis toxin (PT)-insensitive G protein of the family of G(q/11)alp ha was obtained by measuring high-affinity guanosine triphosphatase (G TPase) activity in soluble rat liver membranes. PST increased GTPase a ctivity in a dose-dependent manner. This effect was only slightly inhi bited by PT pretreatment of the membranes, whereas anti-G(q/11)alpha a ntisera blocked most of the PST-stimulated GTPase activity. The select ive association of the PST receptor with this G protein was further st udied by the coelution in wheat germ agglutinin semipurification of th e receptor and by immunoprecipitation of the G protein-PST receptor co mplexes using G-protein-specific antisera. A G protein of the family o f G(q/11)alpha was found to be associated with the semipurified PST re ceptor. Moreover, anti-G(q/11)alpha antisera immunoprecipitated most P ST-binding activity (95%), bringing down most of the specific G protei n, whereas anti-G(il,2)alpha and -G(o,13)alpha failed to immunoprecipi tate the PST-binding activity. Finally, the coupling of the PST recept or with the effector phospholipase C was disrupted by blocking with G( q/11)alpha antisera, suggesting that a G protein of the family of G(q/ 11)alpha is a signal mediator from PST receptors to phospholipase C ac tivation in rat liver membranes.