Receptors taste

Taste buds Taste Profiles Taste receptors Tastes, primary... 

Sapid. Having the power of affecting the taste receptor. 

Sensory receptors expressed in particular in taste receptor cells of the taste buds that sense the five basic tastes salt, sour, sweet, bitter and umami (glutamate taste). Sodium type ion channels sense salty taste whereas sour taste is transduced by potassium type ion channels. The underlying cause of sweet, bitter, and umami tastes is the selective activation of different groups of G protein coupled receptors that discriminate between sweet, bitter, and umami tasting molecules. 

The speed with which taste stimulation occurs, coupled with the fact that stimulation with toxic substances does no damage to the receptors, led Beidler to suggest that taste stimulus need not enter the interior of the taste cell in order to initiate excitation. Because a taste cell has been shown to be sensitive to a number of taste qualities, and to a large number of chemical stimuli, he and his coworkers concluded that a number of different sites of adsorption must exist on the surface of the cell. Therefore, they assumed that taste response results from adsorption of chemical stimuli to the surface of the receptor at given receptor sites. This adsorption is described by a monomolecular reaction similar to that assumed by Renqvist, Lasareff, and Hahn, but with a difference. From the fact that each type of chemical-stimulus compound has a unique level of saturation of the taste receptor, it was concluded that the magnitude of the response is dependent on the initial reaction with the receptor, and not on other, subsequent receptor-reactions that are common to all types of receptor stimulation. Therefore, it was assumed that the magnitude of neural response is directly proportional to the number of sites filled, the maximum response occurring when all of the sites are filled. Beidler derived a fundamental... 

That the initial event of taste stimulation takes place on the cell surface of the taste receptor is now universally accepted. In addition, accumulated evidence strongly suggests that taste-bud stimulation is extracellular in nature. For example, (1) the sweet-taste response is both rapid and reversible, (2) the intensely sweet proteins monellin" and thaumatin could not possibly penetrate the cell, because of their size, and (3) miraculin, the taste-modifying glycoprotein, having a molecular weight of 44,000 would also be too large to penetrate the taste cell. ... 

There is little doubt that Shallenberger s AH,B hypothesis is the most plausible concept in the explanation of the initial stimulation of the sweet-taste receptor. However, it was unfortunate that the evidence was accrued largely with the aid of reducing sugars, which, in solution, equilibrate between many isomers, so that it is not possible to relate total gustatory response to any one particular stereochemical structure It is also not... 

AH,B units at opposite ends of the molecule, just as in the case of l,3-dihydroxy-2-propanone (see Section II,3,a,ii), so that the molecule cannot align itself correctly on the receptor surface.Odorant molecules have been observed to behave similarly. The poor polarization of the taste receptor is enhanced by the combined effect of (a) the absence of a ring-oxygen atom, and hence a polar center, and (b) the presence of hydrophobic, methylene groups. 

Fig. 38.— Polarization of Bitter-Sweet Molecules on Taste Receptors. ...

Taste-modality recognition is a function of the cells of the taste buds. Perception of the sensation is a result of complex processes in the brain. The biological events that are discussed are those that occur, or are suggested as occurring, in taste-receptor cells, beginning at the instant when the taste-stimulus molecule interacts with the cell, until the membrane of the receptor cell is polarized. These are peripheral events. However, our knowledge of the peripheral mechanisms in taste perception is not sufficiently complete to provide a detailed, biophysical explanation of this phenomenon. Nevertheless, several stages in this explanation have been hypothesized, and some are demonstrable. 

The mechanisms by which the taste (and also the olfactory) system senses chemical compounds is assumed to occur by way of a chemoreceptory system that interacts effectively with a broad, structural variety of stimulant molecules, by means of a receptor epithelium consisting of the mosaic of adjacent, peripheral membranes of many receptor cells, exposed to a medium carrying stimulus molecules. A receptor cell is conveniently and, for our present purpose, sufficiently defined as a cell equipped to interact, according to some mechanism, with stimulus molecules, to convert the effect of this interaction into a signal, and to project this signal into the system. The taste receptor is thus a differentiated, epithelial cell synaptically contact-... 

The taste receptors allow for the collection of only a small amount of information, enabling us to distinguish the taste modalities, namely, sweet, bitter, saline, or acid. Responses to the true taste-receptors are produced with a high degree of probability over relatively simple pathways, containing few fibers. The cortical centers for tastes, if present at all, are small. ... 

Hoon M., Adler E., Lindemeier J., Battey J.F., et al. (1999). Putative mammalian taste receptors a class of taste-specific GPCRs with distinct topographic selectivity. Cell 96, 541-551. 

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