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 transducing the proliferative effects have generally been confined to colorectal 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 investigate the binding of I-125-[Met(15)]-gastrin(17)gly to normal colonic crypts. Methods: Crypts were released from normal rat and rabbit colonic mucosa by treatment with EDTA and isolated by centrifugation. The binding of I-125-[Met(15)]-gastrin(17)gly was measured in displacement experiments with increasing concentrations of either gastrin(17)gly, gastrin(17) or gastrin receptor antagonists. The concentrations required for 50% inhibition were determined 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. Binding 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-selective gastrin/CCK receptor antagonists proglumide and benzotript, but not by the cholecystokinin (CCK)-A receptor antagonist L364 718, or the gastrin/CCK-B receptor antagonist L365 260. Conclusion: We conclude that the gastrin(17)gly binding site on normal colonic crypts has properties consistent with the gastrin/CCK-C receptor. (C) 2001 Blackwell Science Asia Pty Ltd.