DIRECT G-PROTEIN ACTIVATION REVERSES IMPAIRED CCK SIGNALING IN HUMAN GALLBLADDERS WITH CHOLESTEROL STONES

Human gallbladders were used to investigate the mechanisms of the impa ired contraction induced by cholecystokinin (CCK) associated with chol esterol stones. Single muscle cells were isolated enzymatically with c ollagenase. Inositol 1,4,5-trisphosphate was measured by high-performa nce liquid chromatography. Diacylglycerol was assayed by thin-layer ch romatography. CCK stimulation showed decreased muscle contraction and production of inositol 1,4,5-trisphosphate and diacylglycerol in gallb ladders with cholesterol stones compared with those with pigment stone s. Exogenous calmodulin induced maximal contraction of 22.4 +/- 0.5 an d 21.0 +/- 0.6% in gallbladders with cholesterol and pigment stones, r espectively. Similar findings were observed with a synthetic diacylgly cerol analogue. Two G protein activators, aluminum fluoride and guanos ine 5'-O-(3-thiotriphosphate), evoked similar responses in these two t ypes of gallbladders, with maximal contractions of 21.3 +/- 0.4 and 23 .3 +/- 0.5%, respectively, in those with cholesterol stones and 20.9 /- 0.8 and 22.6 +/- 0.4%, respectively, in those with pigment stones. These results suggest that receptor-dependent ligands like CCK cannot fully activate the intracellular pathways, which, however, can be full y stimulated by circumventing receptors with G protein activators or s econd messengers. After G protein activation, the pathways appear to b e functionally intact. The defect might then reside in the receptor or in the interaction between receptors and G proteins.