Thermal gating of TRP ion channels: food for thought?
Members of the family of transient receptor potential (TRP) ion channels mediate a wide range of sensory modalities, including thermosensation and taste. Among the "thermo-TRPs," some, such as TRPV1, are activated by warm temperatures, whereas others, such as TRPM8, are activated by cold. How is temperature able to have such strong and opposing effects on these related channels? Although at a structural level the answer to this question is not known, an elegant biophysical model has been proposed that accounts for the different thermosensitivities of TRP channels. This model posits that temperature acts by shifting the inherent weak voltage sensitivity of TRPV1 and TRPM8 in opposite directions, thus promoting opening of TRPV1 at warm temperatures and TRPM8 at cold temperatures. TRPM5, which is distantly related to TRPM8, is a Ca2+-activated cation channel expressed in taste cells that is essential for sweet, bitter, and umami tastes. Like TRPV1 and TRPM8, TRPM5 is weakly sensitive to voltage and thus may also be temperature sensitive. A recent report shows that activity of TRPM5 is increased at warm temperatures, suggesting that heat may enhance the perception of taste through direct modulation of the putative taste transduction channel.
Department of Biological Sciences, Program in Neuroscience, University of Southern California, Los Angeles, CA 90089, USA. liman@usc.edu
Emily R
ER
Liman
D000818:Animals; D003080:Cold Temperature; D006358:Hot Temperature; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology*; D008564:Membrane Potentials; D051379:Mice; D008959:Models, Neurological; D010465:Perception / Q000502:physiology; D043562:Receptors, G-Protein-Coupled / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D050053:TRPM Cation Channels / Q000502:physiology; D050916:TRPV Cation Channels / Q000502:physiology; D013649:Taste / Q000502:physiology; D013696:Temperature; D050051:Transient Receptor Potential Channels / Q000145:classification / Q000502:physiology*
D043562:Receptors, G-Protein-Coupled; D050053:TRPM Cation Channels; C404409:TRPM5 protein, human; C425966:TRPM8 protein, human; D050916:TRPV Cation Channels; C494482:TRPV1 protein, human; D050051:Transient Receptor Potential Channels