The effects of different concentrations of glucose on glucose sensors and GLP-1 secretion in the enteroendocrine cell line STC-1.

Glucose triggers glucagon-like peptide (GLP)-1 secretion from L cells involving several glucose sensors including sodium-glucose transporter (SGLT)1, glucose transporter (GLUT)2, and sweet taste receptors (STRs). This study investigated the effects of different glucose concentrations on GLP-1 secretion, intracellular concentrations of Ca2+ and cAMP, glucose uptake, and protein levels of SGLT1, GLUT2, and STRs in STC-1 cells. Low glucose (5.6 mM) increased GLP-1 secretion, intracellular Ca2+ concentration, and SGLT1 protein level compared with glucose-free group. GLP-1 secretion and intracellular Ca2+ concentration triggered by low glucose were inhibited by the SGLT1 inhibitor. GLP-1 secretion or intracellular Ca2+ concentration in high-glucose (25, 100, 200 mM) groups was significantly higher than that of low-glucose group. Elevation of cAMP level was observed in concentration-dependent manner, and decreased glucose uptake was observed in 100 or 200 mM glucose group. High glucose increased protein levels of STRs and GLUT2 in comparison to low-glucose group. GLP-1 secretion and intracellular levels of Ca2+ and cAMP triggered by high glucose were inhibited in the presence of the GLUT2 or STR inhibitor. These results suggest that SGLT1 is dominantly responsible for GLP-1 secretion triggered by low glucose, and that STRs and GLUT2 are involved in GLP-1 secretion induced by high glucose.