Binding sites for progastrin-derived peptides in colonic crypts

Background and Aims: Gastrin(17)gly acts as a growth factor for the colonic mucosa. Studies on the binding properties of the receptor involved in tran sducing the proliferative effects have generally been confined to colorecta l carcinoma cell lines, and no investigation of gastrin(17)gly receptors on normal colonocytes has yet been reported. The aim of this study was to inv estigate the binding of I-125-[Met(15)]-gastrin(17)gly to normal colonic cr ypts. Methods: Crypts were released from normal rat and rabbit colonic mucosa by treatment with EDTA and isolated by centrifugation. The binding of I-125-[M et(15)]-gastrin(17)gly was measured in displacement experiments with increa sing concentrations of either gastrin(17)gly, gastrin(17) or gastrin recept or antagonists. The concentrations required for 50% inhibition were determi ned by the use of curve fitting. Results: I-125-[Met(15)]-Gastrin(17)gly bound to both rat and rabbit crypts , and displacement experiments with unlabeled gastrin(17)gly revealed that the IC50 values were 1.0 +/- 0.6 and 0.6 +/- 0.2 mu mol/L, respectively. Bi nding was also competed by gastrin(17), with IC50 values of 2.4 +/- 1.7 and 2.4 +/- 0.7 mu mol/L, respectively. Binding was inhibited by the non-selec tive gastrin/CCK receptor antagonists proglumide and benzotript, but not by the cholecystokinin (CCK)-A receptor antagonist L364 718, or the gastrin/C CK-B receptor antagonist L365 260. Conclusion: We conclude that the gastrin(17)gly binding site on normal colo nic crypts has properties consistent with the gastrin/CCK-C receptor. (C) 2 001 Blackwell Science Asia Pty Ltd.