title: Characterization of cholecystokinin receptors on bovine gallbladder membranes.
abstract: Cholecystokinin (CCK) binding to its receptors on a muscularis membrane fraction of bovine gallbladder was characterized using a biologically active CCK-33-[125I]Bolton-Hunter conjugate. Receptor binding was localized to the muscularis layer of the gallbladder; no binding was seen on either mucosal or serosal membranes. At 24 degrees C and pH 6.5, binding was maximal after 60-90 min of incubation, remained at a plateau for at least 240 min, and was reversed by the addition of unlabeled CCK-8. Optimal binding was seen at pH of 5.5 and required the presence of magnesium. Gallbladder binding data, best fit by a two-parameter model using a nonlinear least-squares computer program, was consistent with a single order of binding sites with a Kd of 618 +/- 168 pM and a binding capacity of 100.5 +/- 15.7 fmol/mg prot (mean +/- SE, n = 5). CCK-8 and CCK-33 inhibited 125I-CCK binding to gallbladder membranes with similar potencies, whereas desulfated CCK-8, gastrin I and II, and CCK-4 were at least 500 times less potent than CCK-33. The CCK antagonists dibutyryl cGMP and proglumide inhibited 125I-CCK binding with an IC50 of 31 and 600 microM, respectively. The present studies therefore demonstrate the existence of a specific CCK receptor on bovine gallbladder muscularis membranes with a high degree of selectivity for CCK analogues.
mesh_terms: D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002766:Cholecystokinin / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors / Q000378:metabolism; D005704:Gallbladder / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D009092:Mucous Membrane / Q000378:metabolism; D009130:Muscle, Smooth / Q000378:metabolism; D011817:Rabbits; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011949:Receptors, Cholecystokinin; D012704:Serous Membrane / Q000378:metabolism; D013997:Time Factors
chemical_list: D011956:Receptors, Cell Surface; D011949:Receptors, Cholecystokinin; D002766:Cholecystokinin