Sci. STKE, 20 December 2005
TASTE PERCEPTION Sweeter When It's Hot
Sugar solutions taste sweeter when warm. Talavera et al. now provide a molecular mechanism for this phenomenon. They identified the transient receptor potential (TRP) family members TRPM5 and TRPM4 as thermally activated, calcium-dependent cation channels. TRPM5 and the related protein TRP4 are calcium-impermeable cation channels. When expressed in human embryonic kidney (HEK) 293 cells, these proteins exhibited a shift in voltage dependence in response to increased temperature in the range of 15°C to 35°C, such that at higher temperatures the channels were more active. Activation of the channels by heat required the presence of intracellular calcium, despite the fact that these channels do not conduct calcium ions. Therefore, they are poised to serve as coincidence detectors, sensing a stimulus that increases intracellular calcium concentrations, such as the presence of a taste ligand that activates a taste receptor, as well as temperature. Indeed, knockout mice lacking TRPM5 did not show any increase in responsiveness (chorda tympani nerve stimulation) to sweet compounds when presented at higher temperatures, whereas wild-type mice showed an increased response to sweet, but not bitter or umami, when the temperature was increased. Thus, heat activation of TRPM5 appears to underlie the sensation that warm, sugary tastes are sweeter.
K. Talavera, K. Yasumatsu, T. Voets, G. Droogmans, N. Shigemura, Y. Ninomiya, R. F. Margolskee, B. Nilius, Heat activation of TRPM5 underlies thermal sensitivity of sweet taste. Nature 438, 1022-1025 (2005). [PubMed]
Citation: Sweeter When It's Hot. Sci. STKE 2005, tw452 (2005).
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