Bitter, sweet, and umami signaling in taste cells: it's not as simple as we thought

The taste system uses distinct signaling pathways to detect chemicals in potential food items. Bitter, sweet and umami stimuli have complex chemical structures and activate G protein coupled receptor (GPCR) pathways while salt and sour are detected by ionotropic receptors. The current taste model states that bitter, sweet, and umami stimuli are transduced by Type II taste cells using GPCRs and a common PLCβ2/IP₃R3/TRPM5 signaling pathway. However, there are several caveats to this model that suggest additional signaling mechanisms are involved. Multiple studies have reported that loss of individual signaling components reduces, but does not abolish, taste responses to these stimuli. Recent work has also identified a subset of taste cells that are separate from Type II cells and are broadly responsive to multiple taste qualities, including bitter, sweet and umami. These studies suggest that the signaling processes in taste cells are more complex than previously appreciated.