Abstract
Sweet taste responses in receptor cells are known to occur through a common signaling pathway involving T1R2/T1R3 heterodimeric receptors, G-αgustducin (Ggust) and TRPM5 channels. In mice, sweet responses of the chorda tympani (CT) nerve are classified into two components; one is inhibited by gurmarin [Gur-sensitive (GS)] and the other is not [Gur-insensitive (GI)]. Recently, TRPM5 is found to be a temperature-denpendent increase (TDI) in response to sweeteners. In the current study, we examined GS and GI components to sucrose (Suc), glucose (Glc), saccharin (Sac), SC45647 (SC) in the CT nerve at 15, 25, 35°C of temperature in T1R3-, Ggust- and TRPM5-KO mice. Compared to those in wild type mice, the CT nerve responses of three types of KO mice to Suc, Glc, Sac were either greatly reduced, or abolished in case of SC at every temperature. In T1R3-KO mice, responses to Suc and Glc exhibited TDI and GS. In Ggust-KO mice, responses to Suc and Glc exhibited only TDI. In TRPM5-KO mice, responses to Glc exhibited TDI and GS. The responses to Sac did not exhibit TDI and GS in all KO mice. These results suggest that (1) the GS component may occur through not only TRPM5-dependent (temperature-sensitive) pathway, but also other unknown pathway which may be TRPM5-independent (temperature-sensitive) in Glc responses, and (2) it is possible that Ggust may play an indispensable role in the GS transduction pathway for sweet taste responses in mice. [J Physiol Sci. 2008;58 Suppl:S167]
