Acetylcholine and cholecystokinin receptors functionally couple by different G‐proteins to phospholipase C in pancreatic acinar cells

Abstract

We have studied the involvement of GTP-binding proteins in the stimulation of phospholipase C from rat pancreatic acinar cells. Pretreatment of permeabilized cells with activated cholera toxin inhibited both cholecystokinin-octapeptide (CCK-OP) and GTPyS but not carbachol (CCh)-induced production of inositol trisphosphate. Pertussis toxin had no effect. Neither vasoactive intestinal polypeptide, a stimulator, of adenylyl cyclase, nor the CAMP-analogue, 8-bromo CAMP, mimicked the inhibitory effect of cholera toxin on agonist-induced phospholipase C activation. This indicates that inhibition by cholera toxin could not be attributed to a direct interaction of cholera toxin activated G, with phospholipase C or to an elevation of CAMP. In isolated rat pancreatic plasma membranes cholera toxin ADP-ribosylated a 40 kDa protein, which was inhibited by CCK-OP but not by CCh. We conclude from these data that both CCK-and muscarinic acetylcholine receptors functionally couple to phospholipase C by two different GTP-binding proteins.

Oscillating intracellular Ca2+ signals evoked by activation of receptors linked to inositol lipid hydrolysis: Mechanism of generation

“…In the pancreatic acinar cells, cholecystokinin and acetylcholine, agents that are known to bind to separate receptor sites but both evoke inositol lipid breakdown and Ins (1,4,5) P3 generation (Schnefel et al, 1988), induce somewhat different patterns of Ca 2+ signals (Osipchuk et al, 1990). These findings show that the model in Fig.…”

“…In the case of cholecystokinin action on pancreatic acinat cell membranes it is known that there is, at least at high concentrations, activation ofadenyl cyclase, whereas acetylcholine does not activate this enzyme (Schulz, 1989). Acetylcholine and cholecystokinin receptors interact with different G-proteins and while both these G-proteins can link up with phosphoinositidase C (Schnefel et al, 1988), they may also be able to connect other effectors and these could be different for the two types of G-proteins. It is interesting in this context that internal stimulation of pancreatic acinar cells with GTP-,/-S, that would undoubtedly interact with several different kinds of G-proteins, produces [Ca2+]i changes that seem to combine the patterns characteristic for acetylcholine and cholecystokinin although being perhaps dominated by the latter (Osipchuk et al, 1990).…”

Inhibition of electrical coupling in pairs of murine pancreatic acinar cells by OAG and isolated protein kinase C

“…Different kinase activities have been demonstrated in pancreatic acini, including a cAMP-dependent protein kinase, a Ca2+-calmodulin dependent kinase, and protein kinase C (Burnham & Williams, 1984a;Noguchi et al, 1985). They appear to be differentially activated by secretagogues such as secretin and vasoactive intestinal peptide, which increase the production of cAMP, or cholecystokinin and cholinergic agents, which lead to a G-protein mediated activation of phospholipase C, resulting in an elevation of the intracellular Ca 2+ concentration and protein kinase C activity (Burnham & Williams, 1984b;Merritt et al, 1986;Ishizuka et al, 1987;Schnefel et al, 1988). Activation of PKC and a concomitant increase of amylase release could also be induced by phorbol esters and diacylglycerol (Women & Wrenn, 1984;Merritt & Rubin, 1985).…”

Signal Transduction Mechanisms Involved in Hormonal Ca 2+ Fluxes

“…Further evidence is provided by a) the enhancement of phospholipase C activation by suboptimal concentrations of GTPyS in the presence of agonist, b) an agonist-induced stimulation of GTPase activity, c) the inhibition of phospholipase C activation by GDP,S, d) an inhibition of agonist-induced activation of phospholipase C by toxins (some cell types only), and e) the retention of receptor-G-protein complexes (28-30) or G-proteinphospholipase C complexes (31) during purification. (27,(34)(35)(36)(37). This effect of cholera toxin was independent of ADP-ribosylation of G. and changes of cyclic AMP.…”

“…In platelets, pertussis toxin inhibits thrombin but not U46619 (a thromboxane A2 analogue) responses (33). Further, heterogeneity in the type of G-protein able to couple to phospholipase C is suggested by the ability of cholera toxin to inhibit the effects of Ca2'-mobilizing agonists in a variety of cell types (27,(34)(35)(36)(37). This effect of cholera toxin was independent of ADP-ribosylation of G. and changes of cyclic AMP.…”