Acid detection by taste receptor cells

DeSimone, John A.; Lyall, Vijay; Heck, Gerard L.; Feldman, George M.

doi:10.1016/s0034-5687(01)00293-6

Cited by 67 publications

(54 citation statements)

References 57 publications

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“…Taste cells are bathed in saliva, which has a pH of 6 -7 under ambient conditions but can be further acidified by the ingestion of sour-tasting foods that can have a pH as low as 3 (24). At present, the mechanism of sour transduction is not well understood, and several candidate pH-sensitive ion channels have been proposed to mediate this modality (24). Our observation that TRPM5 is pH-sensitive makes it a candidate to play a role in sour taste transduction.…”

Section: Discussionmentioning

confidence: 99%

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Extracellular Acid Block and Acid-enhanced Inactivation of the Ca2+-activated Cation Channel TRPM5 Involve Residues in the S3-S4 and S5-S6 Extracellular Domains

Liú

Zhang

Liman

2005

Journal of Biological Chemistry

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TRPM5, a member of the superfamily of transient receptor potential ion channels, is essential for the detection of bitter, sweet, and amino acid tastes. In heterologous cell types it forms a nonselective cation channel that is activated by intracellular Ca 2؉ . TRPM5 is likely to be part of the taste transduction cascade, and regulators of TRPM5 are likely to affect taste sensation. In this report we show that TRPM5, but not the related channel TRPM4b, is potently blocked by extracellular acidification. External acidification has two effects, a fast reversible block of the current (IC 50 pH ‫؍‬ 6.2) and a slower irreversible enhancement of current inactivation. Mutation of a single Glu residue in the S3-S4 linker and a His residue in the pore region each reduced sensitivity of TRPM5 currents to fast acid block (IC 50 pH ‫؍‬ 5.8 for both), and the double mutant was nearly insensitive to acidic pH (IC 50 pH ‫؍‬ 5.0). Prolonged exposure to acidic pH enhanced inactivation of TRPM5 currents, and mutant channels that were less sensitive to acid block were also less sensitive to acid-enhanced inactivation, suggesting an intimate association between the two processes. These processes are, however, distinct because the pore mutant H896N, which has normal sensitivity to acid block, shows significant recovery from acid-enhanced inactivation. These data show that extracellular acidification acts through specific residues on TRPM5 to block conduction through two distinct but related mechanisms and suggest a possible interaction between extracellular pH and activation and adaptation of bitter, sweet, and amino acid taste transduction.All animals have evolved mechanisms by which they sense chemicals in the environment and discriminate the nutritious from the noxious. In mammals, taste cells signal the presence of at least five distinct types of chemicals that give us the perceptions of bitter, sour, sweet, salty, and amino acid tastes. Two of these modalities, salty and sour, detect ions (Na ϩ and H ϩ , respectively), and both modalities may be mediated directly by ion channels on the apical surface of taste cells (1). The other three modalities are mediated by distinct G proteincoupled receptors (2-4) that signal through a common transduction cascade, for which both phospholipase C ␤2 and the ion channel TRPM5 are essential elements (5). It is likely that upon binding of taste molecules, sweet, bitter, and amino acid taste receptors initiate a signaling cascade that activates phospholipase C ␤2, leading to the breakdown of phosphatidylinositol 4,5-bisphosphate into inositol trisphosphate and diacylglycerol and the release of Ca 2ϩ from intracellular stores (6, 7). TRPM5 may be the final element of this cascade, converting the biochemical signal transduction pathway into an electrical signal sent to the brain (5, 8). The essential role of TRPM5 in multiple taste pathways suggests that chemicals that modify its activity could have profound effects on taste sensation.TRPM5 belongs to the transient receptor potential (TRP) 1 fa...

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Section: Discussionmentioning

confidence: 99%

“…Weak acids can exist in an undissociated form that can cross cell membranes and thereby acidify intracellular compartments of cells. Indeed, this is believed to be the mechanism for sour taste transduction (24). Fig.…”

Section: Trpm5 Ismentioning

confidence: 98%

Extracellular Acid Block and Acid-enhanced Inactivation of the Ca2+-activated Cation Channel TRPM5 Involve Residues in the S3-S4 and S5-S6 Extracellular Domains

Liú

Zhang

Liman

2005

Journal of Biological Chemistry

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“…Our current knowledge about the detection of sourness is the least advanced of the five main taste senses. Sourness is related to the acidity of food commonly related to the detection of bacterial fermentation products and it typically evokes a rejection response (Lindemann 2001;DeSimone et al 2001;Huang et al 2006). Taste cells that mediate a sour taste are sensitive to intracellular hydrogen ion concentration.…”

Section: Taste (Gustation)mentioning

confidence: 99%

“…Taste cells that mediate a sour taste are sensitive to intracellular hydrogen ion concentration. The TR therefore are the protein complexes that serve as ion channels for the selective entrance of hydrogen ions into the taste cell (Lindemann 2001;DeSimone et al 2001). Hydrogen gated channels used among mammalian species include HCN (named after hyperpolarization-activated cyclic nucleotide-gated channel) among others.…”

Section: Taste (Gustation)mentioning

confidence: 99%

Unfolding the codes of short-term feed appetence in farm and companion animals. A comparative oronasal nutrient sensing biology review

Roura¹,

Humphrey²,

Tedó³

et al. 2008

Can. J. Anim. Sci.

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Roura, E., Humphrey, B., Tedo´, G. and Ipharraguerre, I. 2008. Unfolding the codes of short-term feed appetence in farm and companion animals. A comparative oronasal nutrient sensing biology review. Can. J. Anim. Sci. 88: 535Á558. The evolution of the chemical senses has resulted in a sensory apparatus for high taste and smell acuity in mammals and birds to ensure self-nourishment. Such peripheral chemosensory systems function as a code to unfold the nutritional value of feedstuffs. Food ingestion simultaneously evokes odor, taste and thermo-mechanical (somatosensing) sensations. Olfaction represents the capacity to identify feed volatiles that are predominantly derived from essential nutrients in plants.Comparative biology of olfaction shows that primates and chickens have a smaller olfactory epithelium and fewer olfactory receptor (OR) genes than non-primate mammals studied to date including farm and companion animals, such as the pig, the cow, the dog, the cat and the horse. A significant proportion of the total OR genes in mammals and birds have lost their functionality (pseudogenes) in a process that seems to reflect a decrease in the animal's reliance on the sense of smell, particularly in humans and cows. The taste system allows animals to recognize a diverse repertoire of nutrient (sugars, amino acids, salts, acids and fats) or toxic related chemical entities that provide valuable information about the quality of food. Taste senses non-volatile molecules in the oral cavity through taste receptors (TR). The TR are expressed in the sensory cells forming the taste buds of the tongue's papillae. Taste cells are linked to a network of solitary chemosensory cells diffused through many non-taste tissues involved in metabolic homeostasis. The number of functional taste receptor genes (TASR) in humans is equivalent to that in other mammals and superior to that in chickens. The TASR family 1 (TAS1R coding for umami and sweet TR) is conserved, in number and type, across the species evaluated, with the exception of the sweet receptor in chicken and feline species. The TASR family 2 (TAS2R coding for bitter TR) shows a strong adaptive capacity to dietary sources and digestive physiology across vertebrates. Pseudogenization (loss of gene functionality) in the TAS2R family seems to be a frequent strategy. The implications of oronasal nutrient sensing related to comparative animal feeding strategies and behaviors such as neophobia, feed refusal and hedonic preferences are discussed. Feed palatability and appetence might be one of the main driving forces in short-term feed consumption. Finally, practical applications relevant to animal production are outlined.Key words: Nutrient sensing, taste, olfaction, somatosensing, feed intake, farm, companion animals Roura, E., Humphrey, B., Tedo´, G. et Ipharraguerre, I. 2008. Le code de l'appe´tence a`court terme chez les animaux domestiques et de compagnie. Biologie comparative de la de´tection bucco-nasale des e´le´ments nutritifs. Can. J. Anim. Sci. 88: 535Á558. En e´voluant, ...

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“…In contrast, amino acids, sweeteners, and most bitter tasting stimuli, were found to bind to specific membrane systems. DeSimone, Lyall, Heck and Feldman [8] acknowledged acid stimuli as the unique sources of sour taste, in an investigation of the mechanisms by which acidic stimuli activate taste receptors by means of pH-tracking.…”

Section: Electrical Taste Sour Taste and Phmentioning

confidence: 99%

Revisiting the Relationship Between Electrogustometry and Sour Taste Perception

Stillman

2009

TOOTORJ

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Abstract:In a recent study Ellegård, Goldsmith, Hay, and Morton concluded that electrogustometry is neither mediated by sour taste receptors, nor reflects sour taste quality. While aspects of electric taste await a full explanation, such farreaching claims have significant implications for the future of electrogustometry in clinical practice. The current paper presents a critique of the grounds upon which the arguments were based, and suggests that these conclusions may be premature.Ellegård, Goldsmith, Hay and Morton [1] addressed the contention that taste perception with anodal electrogustometric stimulation is mediated via sour taste receptors. Their stated aim was to evaluate "to what extent electrogustometry relates to an ability to detect sour taste -rather than sweet, salt, or bitter." They reasoned that if anodal stimulation activates sour taste receptors, then the positive predictive values of electrogustometry should be better for sour taste perception than for other taste qualities. They correlated electrogustometric thresholds with visual analogue scale (VAS) ratings to whole mouth and regional applications of taste solutions provided by patients with various disorders that have the potential to affect taste. Because the pattern of predictive values did not favour sour taste they rejected the view that "electrogustometry is mediated by sour taste receptors or even that it reflects the sour taste quality" [1]. Instead they concluded that electrogustometry measures a function of taste perception different from that induced by chemical stimuli.Research has yet to provide definitive answers to some of the questions that are raised concerning electric taste. In the meantime the validity of the arguments upon which conclusions are based must be established, because conclusions such as those reached by Ellegård et al. have significant implications for the future of electrogustometry in clinical practice. Here I challenge the expectation that electrogustometric thresholds should be better predictors of VAS scores from sour-tasting stimuli than from other solutions. ELECTRICAL TASTE, SOUR TASTE, AND pHIt may be tempting to overlook the fact that although an electrogustometer provides a quantitative threshold estimate; the device does not directly measure a taste response. Instead it delivers a stimulus. The ensuing perceptual response is quantified using an operational definition: namely, the current required for a chosen percentage of stimulus detections. Classically the stimulus delivered via electrogustometry was *Address correspondence to this author at the Massey University Albany, Private Bag 102-904 North Shore MSC, Auckland, New Zealand; Tel: 64 9 4140800; Fax: 64 9 414 0831; E-mail: J.A.Stillman@massey.ac.nz referred to as an "adequate" stimulus in view of the liberation of protons in the vicinity of the anode [2]. Acids are, of course, proton donors, and their association with sour taste is reflected in the Latin root of the word acid meaning "to be sour". Sour or soapy tastes have been reported, de...

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Acid detection by taste receptor cells

Cited by 67 publications

References 57 publications

Extracellular Acid Block and Acid-enhanced Inactivation of the Ca2+-activated Cation Channel TRPM5 Involve Residues in the S3-S4 and S5-S6 Extracellular Domains

Extracellular Acid Block and Acid-enhanced Inactivation of the Ca2+-activated Cation Channel TRPM5 Involve Residues in the S3-S4 and S5-S6 Extracellular Domains

Unfolding the codes of short-term feed appetence in farm and companion animals. A comparative oronasal nutrient sensing biology review

Revisiting the Relationship Between Electrogustometry and Sour Taste Perception

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