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The 125I-labeled sulfonated cholecystokinin (CCK) analogue, D-Tyr25(Nle28,31)-CCK(25-33), bound saturably and reversibly to membranes of rat cerebral cortex. The dissociation constant Kd was estimated to be 0.14 nM by Scatchard analysis and 0.40 nM from analyses of dissociation/association rates. Hill coefficients of 0.99, Scatchard plots and drug competition studies were consistent with a single population of binding sites. Dependence on divalent cations and inhibition by guanylyl-imidodiphosphate suggested binding to a receptor coupled to a G protein. Competition studies with CCK-analogues and non-peptide specific antagonists indicated binding to receptor sites of the B-subtype (CCKB). |
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