THE REGULATORY SITE OF FUNCTIONAL GTP-BINDING PROTEIN-COUPLED TO THE HIGH-AFFINITY CHOLECYSTOKININ RECEPTOR AND PHOSPHOLIPASE A(2) PATHWAY IS ON THE G(BETA) SUBUNIT OF G(Q) PROTEIN IN PANCREATIC ACINI

A non-hydrolysable guanosine nucleotide analog, GTP[S] at 200 mu M, stimulated amylase secretion which was inhibited by an anti-phospholipase A(2) (PLA(2)) antibody in permeabilized pancreatic acini, indicating that the PLA(2) pathway is linked to the GTP binding protein. A high affinity cholecystokinin (CCK) receptor agonist, CCK-OPE (10 mu M), and a low affinity receptor agonist,CCK-8 (0.1 mu M), both caused amylase secretion in permeabilized cells. The action of CCK-OPE was abolished by the G(beta) antibody but not by the G(alpha-q,11) antibody, whereas the opposite was true of the CCK-8 response. Biscoclaurine alkaloid isotetrandrine (10 mu M), a specific inhibitor of PLA(2)-coupled G proteins, abolished Ca2+ oscillations and amylase secretion induced by CCK-OPE (0.1-100 nM), but not by CCK-8 (10 pM) in intact acini. Gp antagonist-2A (10 mu M), which inhibits the activation of Gq, also inhibited the actions of CCK-OPE (10 pM-1 mu M) in intact acini. These observations indicate that the functional unit of the heterotrimeric G protein coupled to the high affinity CCK receptor appears to be different from that linked to the low affinity CCK receptor/G(q-alpha) pathway. The regulatory site of this G protein coupled to the high affinity CCK receptor is on the beta subunit of G(q) protein which elicits Ca2+ oscillations and monophasic amylase secretion via the PLA(2) pathway. (C) 1995 Academic Press, Inc.