ANTAGONISTIC EFFECT OF YM022, AN ANTIULCER AGENT IN RATS, ON HUMAN CHOLECYSTOKININ (CCK)(B) GASTRIN RECEPTOR/

We recently isolated a cDNA clone for the human cholecystokinin (CCK)( B)/gastrin receptor and permanently expressed this receptor cDNA in NI H-3T3 cells. [I-125]CCK-8 specifically bound to the membrane of the tr ansfectant, and this binding was displaced by unlabeled CCK-8 with an IC50 of 0.32 nM. Treatment of these cells with CCK-8 increased the int racellular Ca2+ concentration with an EC(50) Of 0.30 nM. Using these c ells expressing functional human CCKB/gastrin receptors, we investigat ed the pharmacological properties of phenacyl),4-benzodiazepin-3-yl]-3 -(3-methylphenyl) urea (YM022), a potent and selective CCKB/gastrin re ceptor antagonist in rats. YM022 potently inhibited [I-125]CCK-8 bindi ng to the membrane with an IC50 of 55 pM and CCK-8-induced Ca2+ mobili zation with that of 7.4 nM. On the other hand, its racemate and enanti omer more weakly inhibited this binding (IC50 Of 110 pM and 11 nM, res pectively) and Ca2+ mobilization (IC50 Of 18 nM and 94 nM, respectivel y). These results indicate that YM022 stereoselectively recognizes the human CCKB/gastrin receptor as a potent antagonist and that the estab lished transfectant is useful for characterization of human CCKB/gastr in-receptor ligands.