Taste perception

At a symposium at the 2006 American Diabetes Association (ADA) Scientific Sessions on the implications of taste perception, Robert F. Margolskee (New York, NY) discussed the molecular biology of taste. Multiple taste buds are contained within papillae of the tongue. Taste receptors are present in cells of the front, side, and posterior portion of the tongue, with different taste responses in different areas. The innervation of the taste buds involves the facial nerves and vagus. Each taste bud contains 50–100 taste receptor cells, specialized epithelial cells with neuron-like properties making contact with taste stimuli in the oral cavity, leading to activation of an intracellular cascade with subsequent neurotransmitter release. Two taste qualities, salty and sour, are mediated by microvilli in the superior portions of the taste receptor cells, with salty taste involving sodium-specific channels and sour taste involving a number of different mechanisms (either receptors or via blockade of apical potassium entry). The three other tastes are bitter, sweet, and umami (Japanese for “delicious,” the taste of monosodium glutamate), all mediated by G-protein receptors. Bitter taste receptors have 25–30 different structures coupled to a specific G-protein, while umami and sweet depend on a different family of taste receptors—T1R2 and T1R3 for sweet, and T1R1 and T1R3 (as well as other complex combinations) for the taste of glutamate. Both the sweet and umami receptors have large extracellular domains.

Sweet taste genetics have been studied in inbred mice strains to determine the saccharine taste locus, with some strains tasting and others not tasting this. In humans, similar studies allowed identification of loci on chromosome 1p38.33 with a candidate gene identified for T1R3, which was previously thought to be …