Abstract
Previous molecular cloning studies provided evidence that several molecules were specifically involved in the taste signal transduction. T1r3 is a component molecule of receptor which responds to sweet and umami substances. Gustducin (Ggust) is a G protein α-subunit and Trpm5 is a cation channel, both of which participate in the signal transduction for sweet, umami and bitter tastes. In the present study, taste responses of the chorda tympani nerve (CT) were compared among mice knocked out each of the taste related genes (T1r3-, Ggust- and Trpm5-KO mice). Compared to those in wild type mice, responses to sweet substances in these 3 KO mice were diminished but not fully abolished. Further analysis on the residual sweet responses using gurmarin (Gur), a inhibitor of sweet responses, revealed that in T1r3 KO mice, responses to sucrose and glycine were clearly inhibited by Gur, whereas no such Gur inhibition was observed in responses to maltose and glucose. In Trpm5 KO mice, CT responses to all sweet compounds tested were more or less inhibited by Gur. In contrast, in Ggust-KO mice no Gur inhibition on sweet responses was observed. These results suggest the possibility that Ggust may play a crucial role in the Gur-sensitive transduction pathway for sweet taste responses in mice. [Jpn J Physiol 55 Suppl:S168 (2005)]
