Umami taste responses are mediated by alpha-transducin and alpha-gustducin.
The sense of taste comprises at least five distinct qualities: sweet, bitter, sour, salty, and umami, the taste of glutamate. For bitter, sweet, and umami compounds, taste signaling is initiated by binding of tastants to G-protein-coupled receptors in specialized epithelial cells located in the taste buds, leading to the activation of signal transduction cascades. Alpha-gustducin, a taste cell-expressed G-protein alpha subunit closely related to the alpha-transducins, is a key mediator of sweet and bitter tastes. Alpha-gustducin knock-out (KO) mice have greatly diminished, but not entirely abolished, responses to many bitter and sweet compounds. We set out to determine whether alpha-gustducin also mediates umami taste and whether rod alpha-transducin (alpha(t-rod)), which is also expressed in taste receptor cells, plays a role in any of the taste responses that remain in alpha-gustducin KO mice. Behavioral tests and taste nerve recordings of single and double KO mice lacking alpha-gustducin and/or alpha(t-rod) confirmed the involvement of alpha-gustducin in bitter (quinine and denatonium) and sweet (sucrose and SC45647) taste and demonstrated the involvement of alpha-gustducin in umami [monosodium glutamate (MSG), monopotassium glutamate (MPG), and inosine monophosphate (IMP)] taste as well. We found that alpha(t-rod) played no role in taste responses to the salty, bitter, and sweet compounds tested or to IMP but was involved in the umami taste of MSG and MPG. Umami detection involving alpha-gustducin and alpha(t-rod) occurs in anteriorly placed taste buds, however taste cells at the back of the tongue respond to umami compounds independently of these two G-protein subunits.
He
Wei
W
Department of Physiology and Biophysics, The Mount Sinai School of Medicine, New York, New York 10029, USA.
Yasumatsu
Keiko
K
Varadarajan
Vijaya
V
Yamada
Ayako
A
Lem
Janis
J
Ninomiya
Yuzo
Y
Margolskee
Robert F
RF
Damak
Sami
S
D000818:Animals; D002814:Chorda Tympani Nerve / Q000502:physiology; D003433:Crosses, Genetic; D005518:Food Preferences; D005838:Genotype; D005930:Glossopharyngeal Nerve / Q000502:physiology; D005971:Glutamates; D006146:Guanidines; D007291:Inosine Monophosphate; D008562:Membrane Glycoproteins / Q000502:physiology; D051379:Mice; D018345:Mice, Knockout; D000644:Quaternary Ammonium Compounds; D011803:Quinine; D011956:Receptors, Cell Surface / Q000502:physiology; D012970:Sodium Glutamate; D013395:Sucrose; D013649:Taste / Q000502:physiology*; D013650:Taste Buds / Q000502:physiology*; D051193:Toll-Like Receptors; D015293:Transducin / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
D005971:Glutamates; D006146:Guanidines; D007291:Inosine Monophosphate; D008562:Membrane Glycoproteins; D000644:Quaternary Ammonium Compounds; D011803:Quinine; D011956:Receptors, Cell Surface; D012970:Sodium Glutamate; D013395:Sucrose; D051193:Toll-Like Receptors; D015293:Transducin; C099860:SC 45647; C075192:gustducin; C043414:denatonium