One Taste Per Cell, but a Common Signaling Cascade

Abstract

There are controversial views of how mammals distinguish the five taste flavors--bitter, sweet, umami (amino acid), salty, and sour. One model asserts that an individual taste receptor cell expresses only one type of taste receptor and therefore only recognizes and transduces signals in response to a single flavor. Alternatively, a single taste receptor cell could express different taste receptors and thus respond broadly to different taste stimuli, possibly through multiple signaling pathways. A study by Zhang et al. favors a separation of taste perception at the cellular level. However, the three different receptor types that recognize sweet-, umami-, and bitter-tasting ligands all impinge on a common signaling cascade that involves phospholipase Cβ2 (PLCβ2) and a transient receptor potential-like channel (TRPM5), both of which have been previously linked to taste transduction. The authors show that both molecules are coexpressed in taste cell receptors of mice. Genetically altered mice lacking both molecules failed to detect sweet, umami, and bitter stimuli. Neurons that normally propagate signals from activated taste cells to the brain failed to generate action potentials in response to any of theses taste modalities. Only bitter taste perception was rescued when PLCβ2 expression was restored in the subpopulation of cells that expressed the bitter taste receptor. Thus, sweet, umami, and bitter tastes are recognized by distinct cell populations, but converge on a common transduction channel through PLCβ2 to trigger a taste response. Y. Zhang, M. A. Hoon, J. Chandrashekar, K. L. Mueller, B. Cook, D. Wu, C. S. Zuker, N. J. P. Ryba, Coding of sweet, bitter, and umami tastes: Different receptor cells sharing similar signaling pathways. Cell 112 , 293-301 (2003). [Online Journal]