Gustatory and extragustatory functions of mammalian taste receptors

An ever increasing number of reports about taste receptors in non-gustatory tissues suggest that these molecules must have additional functions apart from taste. Of the extraoral tissues expressing taste receptors, the gastrointestinal tract received particular attention since evidence is mounting that tastants after being ingested might exert important regulatory roles in digestive and metabolic processes. At present, the G protein-coupled taste receptors for sweet, umami and bitter stimuli along with taste-related signaling molecules have been investigated in various parts of the alimentary canal. While the mechanism linking the gastrointestinal activity of sweet compounds via the activation of sweet taste receptors to metabolic adjustments has been worked out in some detail, other taste receptor mediated gastrointestinal activities are less well understood. The present article summarizes current knowledge on mammalian G protein-coupled taste receptors as well as various aspects of their proposed role in gastrointestinal tissues.