Acting in good taste: nutrient sensors in the gut

[...]sweet taste sensation is initiated by ligand binding to the extracellular domain of the heterodimeric receptor complex formed by the GPCRs T1R2 and T1R3, whereas savoury taste sensation is initiated through a heterodimer of T1R1 and T1R3. 1 The activated intracellular domain of the heterodimeric receptor complex then couples with a specific G protein alpha subunit, G alpha gustducin, resulting in downstream effector signals including increased intracellular calcium. 2 The activity of G alpha gustducin also leads to activation of transient receptor potential ion channel 5 (TRPM5), a cation channel whose downstream effects are not yet well understood. 3 The discovery of G alpha gustducin expression in luminal gut epithelium raised the intriguing possibility that the gut is somehow able to "taste" luminal contents. 4 More recently, taste receptors and their downstream effectors were shown to be expressed within the stomach, proximal small bowel and even the colon. 5 6 These findings suggest that taste sensation may serve an important physiologic role in the gut.