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Binding sites for progastrin-derived peptides in colonic crypts
1University Department of Surgery, Austin Hospital, Austin and Repatriation Medical Centre, Melbourne, Victoria, Australia.
Journal of Gastroenterology and Hepatology
|February 24, 2001
Summary
Gastrin17gly binds to normal colonic crypts, suggesting a role in colonocyte growth. The binding site appears to be a gastrin/cholecystokinin-C receptor, distinct from CCK-A and CCK-B receptors.
Area of Science:
- Gastroenterology
- Molecular Biology
- Cell Biology
Background:
- Gastrin17gly functions as a growth factor for the colonic mucosa.
- Previous studies focused on colorectal carcinoma cell lines, neglecting normal colonocytes.
- Receptor binding for gastrin17gly in normal colonic crypts remained uninvestigated.
Purpose of the Study:
- To investigate the binding of 125I-[Met15]-gastrin17gly to normal colonic crypts.
- To characterize the gastrin17gly binding site on normal colonocytes.
- To determine the receptor subtype involved in gastrin17gly signaling in normal colonic mucosa.
Main Methods:
- Isolation of crypts from normal rat and rabbit colonic mucosa using EDTA and centrifugation.
- Measurement of 125I-[Met15]-gastrin17gly binding via displacement experiments.
- Determination of IC50 values using increasing concentrations of unlabeled gastrin17gly, gastrin17, and receptor antagonists.
Main Results:
- 125I-[Met15]-gastrin17gly demonstrated binding to both rat and rabbit colonic crypts.
- Displacement experiments revealed IC50 values for gastrin17gly and gastrin17 in the micromolar range.
- Binding was inhibited by non-selective gastrin/CCK receptor antagonists but not by selective CCK-A or CCK-B receptor antagonists.
Conclusions:
- The gastrin17gly binding site on normal colonic crypts exhibits characteristics of the gastrin/CCK-C receptor.
- This finding suggests a specific role for gastrin/CCK-C receptors in mediating gastrin17gly's proliferative effects on normal colonocytes.