Taste sensation mechanism

As early as 1848, it had been suggested that sensory receptors transduce only one sensation, independent of the manner of stimulation. Behavioral experiments tend to support this theory. In 1919, Renqvist proposed that the initial reaction of taste stimulation takes place on the surface of the taste-cell membrane. The taste surfaces were regarded as colloidal dispersions in which the protoplasmic, sensory particles and their components were suspended in the liquor or solution to be tested. The taste sensation would then be due to adsorption of the substances in the solution, and equal degrees of sensation would correspond to adsorption of equal amounts. Therefore, the rate of adsorption of taste stimulants would be proportional to the total substances adsorbed. The phenomenon of taste differences between isomers was partly explained by the assumption that the mechanism of taste involves a three-dimensional arrangement for example, a layer of fatty acid floating on water would have its carboxylic groups anchored in the water whereas the long, hydrocarbon ends would project upwards. 

It is noted that, as is shown in Figure 15, the chemicals with different taste-responses show markedly different effects on the dynamic behavior of the phospholipid film. Detail discussion on the chemical response in relation to the mechanism of taste sensation has already been given in a series of studies from our research group [3,42,43]. 

Sweet Taste. The mechanism of sweetness perception has been extensively studied because of its commercial importance. Many substances that vary in chemical structure have been discovered which are similar to the taste of sucrose. Commercial sweeteners include sucralose, acesulfame-K, saccharin, aspartame, cyclamate (Canada) and the protein thaumatin 4), Each sweetener is unique in its perceived sensation because of the time to the onset of sweetness and to maximum sweetness, ability to mask other sensations, persistence, aftertaste and intensity relative to sucrose [TABLE IT. For example, the saccharides, sorbitol and... 

Many people can detect hydrogen cyanide by odor or taste sensation at a concentration of 1 ppm in air while most people can detect 5 ppm. But HCN does not have an offensive odor, and a few people cannot smell it even at toxic levels. OSHA has set 4.7 ppm as the maximum, average safe exposure limit for a 15-minute period. Exposure to 20 ppm of HCN in air causes slight warning symptoms after several hours 50 ppm causes disturbances within an hour 100 ppm is dangerous for exposures of 30 to 60 minutes and 300 ppm can be rapidly fatal unless prompt, effective first aid is administered. A small concentration of cyanide (0.02 to 0.04 mg/L) always exists in a person s body, and the body has a mechanism for continuous removal of small amounts of cyanide129. 

These taste-modifying substances provide an insight into the mechanism of the production of taste sensations and, therefore, are a valuable tool in the study of the interrelationship between taste and chemical structure. 

Human taste response is modified by several plant-derived substances. The detergent sodium dodecyl sulfate, as well as triterpene saponins from the leaves of several plant species (most notably Gymnema sylvestre and Ziziphus jujuba) will temporarily inhibit the sweet taste sensation in man the duration of the effect being about one hour for G. sylvestre and about fifteen minutes for Z. jujuba. The mechanism of action seems to be related, in part, to the surfactant properties of the materials. Structures of the modifiers and possible mechanisms of action are discussed. 

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. 

Side effects of triptans include paresthesias, fatigue, dizziness, flushing, warm sensations, and somnolence. Minor injection site reactions are reported with SC use, and taste perversion and nasal discomfort may occur with intranasal administration. Up to 15% of patients report chest tightness, pressure, heaviness, or pain in the chest, neck, or throat. Although the mechanism of these symptoms is unknown, a cardiac source is unlikely in most patients. Isolated cases of myocardial infarction and coronary vasospasm with ischemia have been reported. 

After the saliva has carried the tastants into the taste bud, they interact with the taste receptors on the surface of the cells, or with ion channels, which are pore-like proteins. Salty and sour tastants act through ion channels, and sweet and bitter sensations are mediated by surface receptors. The different taste submodalities rely on specific mechanisms Na+ flux through Na+... 

The sweet taste and olfactory responses to a variety of stimuli are examples of chemical senses that utilize protein receptors for initial detection of the stimulus. Most bitter compounds have a hydrophobic component which enables their direct interaction with the cell membrane however, some evidence suggests a protein receptor mechanism. The cooling sensation is treated as a chemesthetic sense, where stimulation takes place at the basal membrane. However, compounds that evoke this response have very specific structural limitations, and most are related to menthol. For purposes of discussion, bitter and cooling sensations will be discussed under generalized receptor mechanisms. 

The salty taste is primarily due to sodium ions acting directly on ion channels. Amiloride specifically blocks sodium channels however, it does not block all responses to salt, in cating more than one mechanism for salty sensation. A different compound, 4-aminopyridine, blocks potassium channels but not sodium. This suggests that receptor proteins and second messengers are not uired, and that these stimuli act directly on ion membrane channels. The physiology of the response of cells to salt has been reviewed (7). 

The only product in this category that has been adequately studied is Listerine. Listerine is a mixture of essential oils—thymol, menthol, a eucalyptol, and methylsalicylate. The mechanism of action appears to be related to alteration of the bacterial cell wall. This product is uncharged and has a low substantivity. Adverse effects reported have been a burning sensation and bitter taste. It is available in a 21.6-26.9% alcohol vehicle with a pH of 4.2. Recommended usage is twice daily, and the ADA accepts the product and some of its generic copies for the control of plaque and gingivitis. 

Do these diverse compounds give rise to a common perception of sweetness or to qualitatively different sensations Sweetness does indeed appear to be a unitary percept (Breslin et al. 1994,1996). However, some sweeteners may be discriminable on the basis of their activation of other sensory transduction mechanisms or differences in the temporal properties of their sensory action. For example, the sweetener sodium saccharin activates bitter receptors in some people (Kuhn et al. 2004 Pronin et al. 2007), and also inhibits sweet taste at high concentrations (Galindo-Cuspinera et al. 2006). Sweet proteins such as thaumatin and monellin can have a slow onset or evoke a prolonged sweetness compared with sugars (Faus 2000), likely owing to a relatively high affinity for the sweet taste receptor. 

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