Membrane responses, taste sensation

TASTE SENSATIONS BASED ON GENERAUZED MEMBRANE RESPONSES... 

Aspartame, sweetness production, 28-30 Aspartic acid, as food material, 138-147 Aspartic acid dipeptides, taste, 141-142r Astringpncy, sensation based on generalized membrane responses, 16-18 Automated data analysis and pattern recognition tool kit, 102... 

Taste of amino acids was studied using the taste sensor [23]. Taste of amino acids has had the large attention so far because each of them elicits complicated mixed taste itself, e.g., L-valine produces sweet and bitter tastes at the same time. Thus, there exist detailed data on taste intensity and taste quality of various amino acids by sensory panel tests [26]. The response of the sensor to amino acids was compared with the results of the panel tests, and response potentials from the eight membranes were transformed into five basic tastes by multiple linear regression. This expression of five basic tastes reproduced human taste sensation very well. 

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). 

As humans, we have developed five perceptive senses smell, taste, touch, sight, and hearing. Sensory response is a good example of adaptation at the molecular level and for this we shall examine the potential of the first two. Odor, like taste, is related to a direct contact of molecules with the olfactive (or gustative) epithelium. These membranes or surfaces contain chemo-receptors which upon excitation by a stimulant give characteristic organoleptic sensations. The specific interactions between small molecules and receptors involve an equilibrium between absorption and desorption and can be studied by chemists using models. 

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