GPR40 mediates the effects of FFAs on glucose stimulated insulin secretion and the change of intracellular calcium concentration in pancreatic β cells

Abstract

Objective To investigate whether G-protein coupled receptor 40(GPR40)mediates short-term and long-term effects of free fatty acids (FFAs) on glucose stimulated insulin secretion (GSIS) and the change of [Ca2+]i in mouse insulinoma NIT-1 cells.Methods The expression of GPR40 in NIT-1 cells was inhibited by siRNA.The short-term and long-term effects of saturated (palmitate) or unsaturated (oleate) fatty acids on GSIS in NIT-1 cells transfected with GPR40 siRNA were examined.Insulin was measured by ELISA.The change in intracellular calcium concentration was observed by laser confocal scanning microscopy after NIT-1 cells were incubated with Fluo-3/AM.Results The short-term treatment of FFAs increased GSIS from NIT-1 cells transfected with control siRNA or mock(P＜0.01),but not from cells transfected with GPR40 siRNA.The exposure of mock,control siRNA transfected cells to FFAs for 48 h resulted in attenuation of GSIS compared to nonexposed cells.In contrast,insulin secretion from cells transfected with GPR40 siRNA was not impaired by exposure to FFAs for 48 h.After incubation with FFAs for 2 h,the maximal fluorescence intensity in control siRNA transfected cells was higher compared with that in GPR40 siRNA transfected cells during the process of GSIS(P＜0.05).However,after incubation with FFAs for 48 h,the maxiaml fluorescence intensity in control siRNA transfected cells was lower than that in GPR40 siRNA transfected cells during the process of GSIS (P ＜ 0.05).Conclusion GPR40 is implicated in mediating the short-term and long-tern effects of FFAs on GSIS and the change of intracellular calcium concentration. Key words: G-protein coupled receptor 40; Free fatty acids; Diabetes mellitus，type 2; Insulin; Ca2+