Sweet, bitter and umami receptors: a complex relationship.

Sweet and bitter are taste qualities linked to food acceptance and rejection in humans. It was long thought that these taste sensations were closely related, but the discovery and characterization of taste receptors revealed that mammals express a single sweet receptor and many unrelated bitter receptors. Bitter-tasting chiral isomers of sweet compounds can bind to the umami receptor, rather than bitter receptors, and elicit the bitter sensation through crosstalk between labelled cells. In support of crosstalk between labelled cells, recent findings suggest that, although most receptor taste cells respond to only one taste, most presynaptic taste cells accept signals from labelled cells that respond to two or more different taste qualities.