Characterization of cholecystokinin receptors on bovine gallbladder membranes

Publisher Website
Google Scholar
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.degree. 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 Mg. Gallbladder binding data, best fit by a 2-parameter model using a nonlinear least-squares computer program, was consistent with a single order of binding sites with Kd of 618 .+-. 168 pM and a binding capacity of 100.5 .+-. 15.7 fmol/mg protein (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 [mean inhibitory concentration] of 31 and 600 .mu.M, respectively. The existence of a specific CCK receptor on bovine gallbladder muscularis membranes with a high degree of selectivity for CCK analogs was thus demonstrated.

This publication has 13 references indexed in Scilit: