title: Characterization of the binding of [3H]-(+/-)-L-364,718: a new potent, nonpeptide cholecystokinin antagonist radioligand selective for peripheral receptors.
abstract: [3H]-(+/-)-L-364,718 a new, potent and selective nonpeptide peripheral cholecystokinin (CCK) antagonist bound saturably and reversibly to rat pancreatic membranes. The radioligand recognized a single class of binding sites with a high affinity (Kd = 0.23 nM). The binding of [3H]-(+/-)-L-364,718 was stereospecific in that the more biologically active (-)-enantiomer demonstrated greater potency than the (+)-enantiomer. The rank order of potency of various CCK agonists and antagonists in displacing [3H]-(+/-)-L-364,718 correlated with their ability to displace [125I]CCK-8 and their known pharmacological activities in peripheral tissues. However, the absolute potencies of agonists were greater in displacing [125I]CCK-8 than [3H]-(+/-)-L-364,718. As described for other physiologically relevant receptor systems, the potency for displacement of [3H]-(+/-)-L-364,718 binding by CCK agonists, but not antagonists, was reduced by guanosine 5'-(beta, gamma-imido)triphosphate and NaCl and enhanced by MgCl2. [3H]-(+/-)-L-364,718 also demonstrated specific binding to bovine gall bladder tissue but not guinea pig brain or gastric glands, consistent with its selectivity as a peripheral CCK antagonist. [3H]-(+/-)-L-364,718 binding to pancreatic membranes was not affected by various pharmacological agents known to interact with other common peptide and nonpeptide receptor systems. These data indicate that [3H]-(+/-)-L-364,718 represents a new potent nonpeptide antagonist radioligand for the study of peripheral CCK receptors which may allow differentiation of agonist and antagonist interactions.
mesh_terms: D000818:Animals; D001570:Benzodiazepinones / Q000378:metabolism*; D002766:Cholecystokinin / Q000037:antagonists & inhibitors* / Q000494:pharmacology; D020109:Devazepide; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D010179:Pancreas / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011949:Receptors, Cholecystokinin; D012965:Sodium Chloride / Q000494:pharmacology; D013237:Stereoisomerism; D014316:Tritium
chemical_list: D001570:Benzodiazepinones; D011956:Receptors, Cell Surface; D011949:Receptors, Cholecystokinin; D014316:Tritium; D006165:Guanylyl Imidodiphosphate; D012965:Sodium Chloride; D002766:Cholecystokinin; D020109:Devazepide