Background and purpose
The G protein-coupled receptor 119 (GPR119) mediates insulin secretion from pancreatic β cells and glucagon-like peptide 1 (GLP-1) release from intestinal L cells. While GPR119-mediated insulin secretion is glucose dependent, it is not clear whether or not GPR119-mediated GLP-1 secretion similarly requires glucose. This study was designed to address the glucose-dependence of GPR119-mediated GLP-1 secretion, and to explore the cellular mechanisms of hormone secretion in L cells versus those in β cells. Experimental approach: GLP-1 secretion in response to GPR119 agonists and ion channel modulators, with and without glucose, was analysed in the intestinal L cell line GLUTag, in primary intestinal cell cultures and in vivo. Insulin secretion from Min6 cells, a pancreatic β cell line, was analysed for comparison. Key
Purpose
The G protein-coupled receptor 119 (GPR119) mediates insulin secretion from pancreatic β cells and glucagon-like peptide 1 (GLP-1) release from intestinal L cells. While GPR119-mediated insulin secretion is glucose dependent, it is not clear whether or not GPR119-mediated GLP-1 secretion similarly requires glucose. This study was designed to address the glucose-dependence of GPR119-mediated GLP-1 secretion, and to explore the cellular mechanisms of hormone secretion in L cells versus those in β cells. Experimental approach: GLP-1 secretion in response to GPR119 agonists and ion channel modulators, with and without glucose, was analysed in the intestinal L cell line GLUTag, in primary intestinal cell cultures and in vivo. Insulin secretion from Min6 cells, a pancreatic β cell line, was analysed for comparison. Key
Results
In GLUTag cells, GPR119 agonists stimulated GLP-1 secretion both in the presence and in the absence of glucose. In primary mouse colon cultures, GPR119 agonists stimulated GLP-1 secretion under glucose-free conditions. Moreover, a GPR119 agonist increased plasma GLP-1 in mice without a glucose load. However, in Min6 cells, GPR119-mediated insulin secretion was glucose-dependent. Among the pharmacological agents tested in this study, nitrendipine, an L-type voltage-dependent calcium channel blocker, dose-dependently reduced GLP-1 secretion from GLUTag cells, but had no effect in Min6 cells in the absence of glucose. Conclusions and implications: Unlike that in pancreatic β cells, GPR119-mediated GLP-1 secretion from intestinal L cells was glucose-independent in vitro and in vivo, probably because of a higher basal calcium tone in the L cells.