The taste transduction channel TRPM5 is a locus for bitter-sweet taste interactions.
Ordinary gustatory experiences, which are usually evoked by taste mixtures, are determined by multiple interactions between different taste stimuli. The most studied model for these gustatory interactions is the suppression of the responses to sweeteners by the prototype bitter compound quinine. Here we report that TRPM5, a cation channel involved in sweet taste transduction, is inhibited by quinine (EC(50)=50 microM at -50 mV) owing to a decrease in the maximal whole-cell TRPM5 conductance and an acceleration of channel closure. Notably, quinine inhibits the gustatory responses of sweet-sensitive gustatory nerves in wild-type (EC(50)= approximately 1.6 mM) but not in Trpm5 knockout mice. Quinine induces a dose- and time-dependent inhibition of TRPM5-dependent responses of single sweet-sensitive fibers to sucrose, according to the restricted diffusion of the drug into the taste tissue. Quinidine, the stereoisomer of quinine, has similar effects on TRPM5 currents and on sweet-induced gustatory responses. In contrast, the chemically unrelated bitter compound denatonium benzoate has an approximately 100-fold weaker effect on TRPM5 currents and, accordingly, at 10 mM it does not alter gustatory responses to sucrose. The inhibition of TRPM5 by bitter compounds constitutes the molecular basis of a novel mechanism of taste interactions, whereby the bitter tastant inhibits directly the sweet transduction pathway.
Talavera
Karel
K
Laboratory of Ion Channel Research, Dept. of Molecular Cell Biology, Herestraat 49, Campus Gasthuisberg, O&N1, KU Leuven, B-3000 Leuven, Belgium. karel.talavera@med.kuleuven.be
Yasumatsu
Keiko
K
Yoshida
Ryusuke
R
Margolskee
Robert F
RF
Voets
Thomas
T
Ninomiya
Yuzo
Y
Nilius
Bernd
B
D000818:Animals; D002478:Cells, Cultured; D002814:Chorda Tympani Nerve / Q000187:drug effects / Q000502:physiology; D004553:Electric Conductivity; D006801:Humans; D015640:Ion Channel Gating / Q000187:drug effects; D051379:Mice; D018408:Patch-Clamp Techniques; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D011802:Quinidine / Q000494:pharmacology; D011803:Quinine / Q000494:pharmacology*; D013395:Sucrose / Q000494:pharmacology; D050053:TRPM Cation Channels / Q000187:drug effects / Q000502:physiology*; D013649:Taste / Q000187:drug effects / Q000502:physiology*
D000644:Quaternary Ammonium Compounds; D011802:Quinidine; D011803:Quinine; D013395:Sucrose; D050053:TRPM Cation Channels; C437888:TRPM4 protein, human; C498617:Trpm5 protein, mouse; C043414:denatonium