Glucose-Sensing Receptor T1R3: A New Signaling Receptor Activated by Glucose in Pancreatic β-Cells

Subunits of the sweet taste receptors T1R2 and T1R3 are expressed in pancreatic beta-cells. Compared with T1R3, mRNA expression of T1R2 is considerably lower. At the protein level, expression of T1R2 is un-detectable in beta-cells. Accordingly, a major component of the sweet taste-sensing receptor in beta-cells may be a homodimer of T1R3 rather than a heterodimer of T1R2/T1R3. Inhibition of this receptor by gurmarin or deletion of the T1R3 gene attenuates glucose-induced insulin secretion from beta-cells. Hence the T1R3 homodimer functions as a glucose-sensing receptor (GSR) in pancreatic beta-cells. When GSR is activated by the T1R3 agonist sucralose, elevation of intracellular ATP concentration ([ATP](i)) is observed. Sucralose increases [ATP](i) even in the absence of ambient glucose, indicating that sucralose increases [ATP](i) not simply by activating glucokinase, a rate-limiting enzyme in the glycolytic pathway. In addition, sucralose augments elevation of [ATP](i) induced by methylsuccinate, suggesting that sucralose activates mitochondrial metabolism. Nonmetabolizable 3-O-methylglucose also increases [ATP](i) and knockdown of T1R3 attenuates elevation of [ATP](i) induced by high concentration of glucose. Collectively, these results indicate that the T1R3 homodimer functions as a GSR; this receptor is involved in glucose-induced insulin secretion by activating glucose metabolism probably in mitochondria.