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pubmed:abstractText |
Human gallbladders were used to investigate the mechanisms of the impaired contraction induced by cholecystokinin (CCK) associated with cholesterol stones. Single muscle cells were isolated enzymatically with collagenase. Inositol 1,4,5-trisphosphate was measured by high-performance liquid chromatography. Diacylglycerol was assayed by thin-layer chromatography. CCK stimulation showed decreased muscle contraction and production of inositol 1,4,5-trisphosphate and diacylglycerol in gallbladders with cholesterol stones compared with those with pigment stones. Exogenous calmodulin induced maximal contraction of 22.4 +/- 0.5 and 21.0 +/- 0.6% in gallbladders with cholesterol and pigment stones, respectively. Similar findings were observed with a synthetic diacylglycerol analogue. Two G protein activators, aluminum fluoride and guanosine 5'-O-(3-thiotriphosphate), evoked similar responses in these two types 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 fully stimulated by circumventing receptors with G protein activators or second messengers. After G protein activation, the pathways appear to be functionally intact. The defect might then reside in the receptor or in the interaction between receptors and G proteins.
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