- GPR40 is a G protein-coupled receptor expressed preferentially in β cells, that has been implicated in mediating free fatty acid-stimulated insulin release. GPR40 RNAi impaired the ability of palmitic acid (PA) to increase both insulin secretion and intracellular calcium ([Ca 2+ ] i ). The PA-dependent [Ca 2+ ] i increase was attenuated by inhibitors of Gαq, PLC, and SERCA. Thus GPR40 activates the Gαq pathway, leading to release of Ca 2+ from the ER. Yet the GPR40-dependent [Ca 2+ ] i rise was dependent on extracellular Ca 2+ and elevated glucose, and was blocked by inhibition of L-type calcium channels (LTCC) or opening of the K ATP channel; this suggests that GPR40 promotes Ca 2+ influx through up-regulation of LTCC pre-activated by glucose and membrane depolarization. Taken together, the data indicate that GPR40 mediates the increase in [Ca 2+ ] i and insulin secretion through the Gαq–PLC pathway, resulting in release of Ca 2+ from the ER and leading to up-regulation of Ca 2+ influx via LTCC.