title: Occurrence of two cholecystokinin binding sites in guinea-pig brain cortex.
abstract: Saturation experiments of the highly potent cholecystokinin analogue [3H]Boc(diNle28,31)CCK27-33 ([3H]BNDL-CCK7, 100 Ci/mmol) with guinea pig brain cortex in a large concentration range (0.05 nM to 30 nM) show the presence of two different binding sites (A site: KD = 0.13 nM, Bmax = 35 fmol/mg; B site: KD = 6.4 nM, Bmax = 92 fmol/mg). Both sites exhibit different sensitivity to sodium ions and therefore can be selectively investigated at [3H]BDNL-CCK7 concentration lower than 1 nM for the A site in Tris buffer and in Krebs buffer for the B site. The selectivity factors KIB/KIA of various CCK related peptides vary from 58 for CCK4 to 26 for CCK8 and 4 for the antagonist (Nle28,31) CCK27-32-NH2. The occurrence of two different CCK binding sites in the brain could explain biphasic pharmacological effects of CCK8.
mesh_terms: D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism*; D002766:Cholecystokinin / Q000378:metabolism*; D006168:Guinea Pigs; D007700:Kinetics; D008566:Membranes / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011949:Receptors, Cholecystokinin
chemical_list: D011956:Receptors, Cell Surface; D011949:Receptors, Cholecystokinin; D002766:Cholecystokinin