M1714 Functional Role of Calcium-Sensing Receptor on Somatostatin Release From Rat Gastric Mucosa

Abstract

G A A b st ra ct s profiles and examined the effects of 5-HT and GLP-1 on EC and L cells respectively to assess the likelihood of an interactive functional relationship between these neuroendocrine cells. Methods: We used an adenocarcinoma cell line (NCI-H716) as a model for L cells and the KRJ-1 cell line as a model for EC cells. Duodenal mucosa was used to studied hormone release ex vivo. Receptor expression was identified using real-time PCR and western blot. The WST-1 proliferation assay was used to assess cell proliferation in response to exendin-4 (long-acting GLP-1 agonist) and 5HT. 5HT and GLP1 secretion was assessed (ELISA) and signaling pathways investigated (cAMP ELISA and MAPK phosphorylation). Results: EC cells express GLP receptor mRNA and protein. L cells express 5HT1A and 5HT2A receptor mRNA and protein but not 5HT2B, 5HT2C, or 5HT3A mRNA. Exendin4 promoted proliferation of EC cells and L cells at high concentration (10uM). 5HT has no effect on proliferation of L cells. Exendin-4 decreased 5HT secretion from EC cells (25%35% decrease, p=0.02) with an ~IC50=1nM. This was associated with a 25-45% (p<0.05) decrease in intracellular cAMP and MAPK phosphorylation and could be reversed by the GLP1 antagonist (GLP8-38). Addition of exendin-4 to isolated duodenal tissue also inhibited serotonin release (30-40% decrease, p=0.024). 5HT treatment has no significant effect on GLP-1 secretion from L cells. Conclusion: GLP-1 is a proliferative agent for neoplastic EC cells at micromolar concentrations. In contrast, at physiological (nanomolar) concentrations, GLP1 inhibits EC cell 5HT secretion via cAMP/MAPK-mediated pathways. Given the central role of EC cells in regulating GI function (motility, secretion, nociception), it is possible that the L cell plays a key up-stream regulatory role in these phenomenon. These results also suggest that EC cell proliferation is not an independent event and that other neuroendocrine cells may regulate EC function and play a role in NET development.