Transmembrane channel-like 4 is involved in pH and temperature-dependent modulation of salty taste

Human susceptibility to NaCl varies depending on temperature and pH, the molecular mechanisms of which remain unclear. The voltage-dependent chloride channel, transmembrane channel-like 4 (TMC4), is activated at approximately 40 °C and is suppressed at pH 5.5. As these are similar in character to human sensory evaluations, hTMC4 may be involved in human salt taste reception.

Does ENaC Work as Sodium Taste Receptor in Humans?

Taste reception is fundamental for the proper selection of food and beverages. Among the several chemicals recognized by the human taste system, sodium ions (Na+) are of particular relevance. Na+ represents the main extracellular cation and is a key factor in many physiological processes. Na+ elicits a specific sensation, called salty taste, and low-medium concentrations of table salt (NaCl, the common sodium-containing chemical we use to season foods) are perceived as pleasant and appetitive. How we detect this cation in foodstuffs is scarcely understood. In animal models, such as the mouse and the rat, the epithelial sodium channel (ENaC) has been proposed as a key protein for recognizing Na+ and for mediating preference responses to low-medium salt concentrations. Here, I will review our current understanding regarding the possible involvement of ENaC in the detection of food Na+ by the human taste system.

LINGUO-CULTURAL SEMANTICS OF ORGANOLEPTIVES IN GLUTTONIC FRAME

In the article S.M. Rudenko made an attempt of a comprehensive study of linguocultural semantics of terminal organoleptics – language signs of the peripheral zone of the gluttonic frame, which are a mental analogue of the perceptual characteristics of units of its nuclear zone. Folklore, ethnographic, ethnolinguistic, lexicographic and popular science sources were taken as a material for research. It is emphasized that in order to denote taste reception, modern Ukrainian language has a wide range of absolutely different units – from word to text. The main representatives of the analyzed case are the nominations of taste, smell, appearance, color, design of dishes and products, however, units representing sound, touch, and consistency also play an important role in describing food perception. Their semantics has cultural characteristics. In the course of the study, it was found that semantic features were invested in a special form of expression such as taste sensation, intensity (degree sign of the degree of manifestation or influence of taste omissions), assessment (positive or negative characteristic of taste sensations in terms of personal, subjective criteria; the presence or lack of evidence); syncretism (indivisibility) of sensory perception of taste and tactile sensations, taste and smell. Phraseological units of the Ukrainian language, which include gustative elements, are used not only in the language of gluttony, but also in the process of nominating the concepts of other areas of human activity, in particular the highest emotional. Text units, which reflect the model of color matching of dishes to the consumer’s taste expectations are of great importance. The obtained results make it possible to make a conclusion that the semantics of organoleptics in the gluttonic frame reflect both taste preferences developed over the centuries-old history of the Ukrainian people and its specific worldview character.

Decrease in rat taste receptor cell intracellular pH is the proximate stimulus in sour taste transduction

Taste receptor cells (TRCs) respond to acid stimulation, initiating perception of sour taste. Paradoxically, the pH of weak acidic stimuli correlates poorly with the perception of their sourness. A fundamental issue surrounding sour taste reception is the identity of the sour stimulus. We tested the hypothesis that acids induce sour taste perception by penetrating plasma membranes as H+ ions or as undissociated molecules and decreasing the intracellular pH (pHi) of TRCs. Our data suggest that taste nerve responses to weak acids (acetic acid and CO2) are independent of stimulus pH but strongly correlate with the intracellular acidification of polarized TRCs. Taste nerve responses to CO2 were voltage sensitive and were blocked with MK-417, a specific blocker of carbonic anhydrase. Strong acids (HCl) decrease pHi in a subset of TRCs that contain a pathway for H+ entry. Both the apical membrane and the paracellular shunt pathway restrict H+ entry such that a large decrease in apical pH is translated into a relatively small change in TRC pHi within the physiological range. We conclude that a decrease in TRC pHi is the proximate stimulus in rat sour taste transduction.