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Animals use sour taste to avoid spoiled food and to choose foods containing vitamins and minerals. To investigate the response to sour taste substances during vitamin C (ascorbic acid; AA) deficiency, we conducted behavioral, neural, anatomical, and molecular biological experiments with osteogenic disorder Shionogi/Shi Jcl- od / od rats, which lack the ability to synthesize AA. Rats had higher 3 mM citric acid and 10 mM AA preference scores when AA-deficient than when replete. Licking rates for sour taste solutions [AA, citric acid, acetic acid, tartaric acid, and HCl] were significantly increased during AA deficiency relative to pre- and postdeficiency. Chorda tympani nerve recordings were conducted to evaluate organic acid taste responses in the AA-deficient and replete rats. Nerve responses to citric acid, acetic acid, and tartaric acid were significantly diminished in AA-deficient rats relative to replete controls. There was no significant difference in the number of fungiform papillae taste buds per unit area in the AA-deficient rats relative to the replete rats. However, mRNA expression levels of Gnat3 (NM_173139.1), Trpm5 (NM_001191896.1), Tas1r1 (NM_053305.1), Car4 (NM_019174.3), and Gad1 (NM_017007.1) in fungiform papillae taste bud cells from AA-deficient rats were significantly lower than those in replete rats. Our data suggest that AA deficiency decreases avoidance of acids and reduces chorda tympani nerve responses to acids. AA deficiency downregulates some taste-related genes in fungiform papillae taste bud cells. However, the results also reveal that the mRNA expression of some putative sour taste receptors in fungiform papillae taste bud cells is not affected by AA deficiency. [ABSTRACT FROM AUTHOR]

Taste cells are a heterogeneous population of sensory receptors that undergo continuous turnover. Different chemo‐sensitive cell lines rely on action potentials to release the neurotransmitter onto nerve endings. The electrical excitability is due to the presence of a tetrodotoxin‐sensitive, voltage‐gated sodium current (INa) similar to that found in neurons. Since the biophysical properties of neuronal INa change during development, we wondered whether the same also occurred in taste cells. Here, we used the patch‐clamp recording technique to study INa in salt‐sensing cells (sodium cells) of rat fungiform papillae. We identified these cells by exploiting the known blocking effect of amiloride on ENaC, the sodium (salt) receptor. Based on the amplitude of INa, which is known to increase during development, we subdivided sodium cells into two groups: cells with small sodium current (SSC cells; INa < 1 nA) and cells with large sodium current (LSC cells; INa > 1 nA). We found that: the voltage dependence of activation and inactivation significantly differed between these subsets; a slowly inactivating sodium current was more prominent in LSC cells; membrane capacitance in SSC cells was larger than in LSC cells. mRNA expression analysis of the α‐subunits of voltage‐gated sodium channels in fungiform taste buds supported the functional data. Lucifer Yellow labelling of recorded cells revealed that our electrophysiological criterion for distinguishing two broad groups of taste cells was in good agreement with morphological observations for cell maturity. Thus, all these findings are consistent with developmental changes in the voltage‐dependent properties of sodium‐taste cells. Key points: Taste cells are sensory receptors that undergo continuous turnover while they detect food chemicals and communicate with afferent nerve fibres.The voltage‐gated sodium current (INa) is a key ion current for generating action potentials in fully differentiated and chemo‐sensitive taste cells, which use electrical signalling to release neurotransmitters.Here we show that, during the maturation of rat taste cells involved in salt detection (sodium cells), the biophysical properties of INa, such as voltage dependence of activation and inactivation, change significantly.Our results help reveal how taste cells gain electrical excitability during turnover, a property critical to their operation as chemical detectors that relay sensory information to nerve fibres. [ABSTRACT FROM AUTHOR]

Zinc is an essential trace element, and its deficiency causes taste dysfunction. Zinc accumulates in zinc transporter (ZnT)3-expressing presynaptic vesicles in hippocampal neurons and acts as a neurotransmitter in the central nervous system. However, the distribution of zinc and its role as a signal transmitter in taste buds remain unknown. Therefore, we examined the distribution of zinc and expression profiles of ZnT3 in taste cells and evaluated zinc release from isolated taste cells upon taste stimuli. Taste cells with a spindle or pyriform morphology were revealed by staining with the fluorescent zinc dye ZnAF-2DA and autometallography in the taste buds of rat circumvallate papillae. Znt3 mRNA levels were detected in isolated taste buds. ZnT3-immunoreactivity was found in phospholipase-β2-immunopositive type II taste cells and aromatic amino acid decarboxylase-immunopositive type III cells but not in nucleoside triphosphate diphosphohydrolase 2-immunopositive type I cells. Moreover, we examined zinc release from taste cells using human transient receptor potential A1-overexpressing HEK293 as zinc-sensor cells. These cells exhibited a clear response to isolated taste cells exposed to taste stimuli. However, pretreatment with magnesium-ethylenediaminetetraacetic acid, an extracellular zinc chelator - but not with zinc-ethylenediaminetetraacetic acid, used as a negative control - significantly decreased the response ratio of zinc-sensor cells. These findings suggest that taste cells release zinc to the intercellular area in response to taste stimuli and that zinc may affect signaling within taste buds.

The objective of this study was to investigate the effects of chronic administration of caffeine on the anatomical characteristics of taste buds, the expression level of taste receptor protein in mice, and preference for a palatable solution. We found that following a 21-day administration of caffeine, mice showed increased behavioural responses to sweet stimuli (acesulfame-K solution). Mirroring this behavioural change, chronic caffeine treatment evidently decreased the maximal cross-sectional area and height of the longitudinal axis of fungiform taste buds, the number of taste cells per fungiform taste bud, and the expression of G protein α-gustducin, while the expression of the sweet taste receptors T1R2 and T1R3 was reversed. Our findings demonstrate that chronic administration of caffeine has an impact on taste sensitivity and changes in taste bud features, which may contribute to the alteration of taste behaviour. [ABSTRACT FROM AUTHOR]

Taste buds are complex sensory organs embedded in the epithelium of fungiform papillae (FP) and circumvallate papillae (CV). The sweet, bitter, and umami tastes are sensed by type II taste cells that express taste receptors (Tas1rs and Tas2rs) coupled with the taste G-protein α-gustducin. Recent studies revealed that the taste response profiles of α-gustducin-expressing cells are different between FP and CV, but which genes could generate such distinctive cell characteristics are still largely unknown. We performed a comprehensive transcriptome analysis on α-gustducin-expressing cells in mouse FP and CV by single-cell RNA sequencing combined with fluorescence-activated cell sorting. Transcriptome profiles of the α-gustducin-expressing cells showed various expression patterns of taste receptors. Our clustering analysis defined the specific cell populations derived from FP or CV based on their distinct gene expression. Immunohistochemistry confirmed the specific expression of galectin-3, encoded by Lgals3 , which was recognized as a differentially expressed gene in the transcriptome analysis. Our work provides fundamental knowledge toward understanding the genetic heterogeneity of type II cells, potentially revealing differential characterization of FP and CV taste bud cells. • Newly developed cell collection method can capture specific taste cell populations. • Specific marker genes were detected in fungiform vs circumvallate taste cells. • Tas2r gene expression was much more variable in circumvallate vs fungiform papillae. • Some specific genes were expressed only in Tas1r - or in Tas2r -dominant cells. [ABSTRACT FROM AUTHOR]

Sophorolipids (SL) are typically produced and secreted by select nonpathogenic yeast species (i.e., Candida) from renewable substrates. They are currently being used by industry on a limited basis in formulations for cleaning solutions as well as laundry and dishwashing detergents. Due to the nature of their chemical structure, it was hypothesized that SL would demonstrate taste‐sensory properties. In this study, SL were produced via fermentation on a mixed substrate platform with glucose and either palmitic acid, stearic acid, or oleic acid using Candida (currently reclassified as Starmerella) bombicola ATCC 22214. The taste properties of SL were determined using a single‐cell manual calcium imaging technique on cultured human fungiform taste papillae (HBO) cells. The results of those studies demonstrated that sweetener‐responsive HBO cells also respond to SL, and these responses are mediated by the type 1 taste receptors 3 (T1R3), because they were blocked by lactisole (a T1R3 receptor‐specific blocker). The involvement of the T1R3 receptor in SL recognition was confirmed via the chorda tympani nerve recording (CTNR) study in a (−/−) T1R3 knockout (KO) mouse model. We further demonstrated that SL are capable of blocking the bitter stimuli‐elicited responses both in HBO cells and in the CTNR study. This is the first report demonstrating that SL have taste‐sensory properties, which opens up numerous possibilities for practical applications of SL to ameliorate bitter tastes in foods and drugs and understand the potential source of dysgeusia in some patients. [ABSTRACT FROM AUTHOR]

The human enteroendocrine L cell line NCI-H716, expressing taste receptors and taste signaling elements, constitutes a unique model for the studies of cellular responses to glucose, appetite regulation, gastrointestinal motility, and insulin secretion. Targeting these gut taste receptors may provide novel treatments for diabetes and obesity. However, NCI-H716 cells are cultured in suspension and tend to form multicellular aggregates, preventing high-throughput calcium imaging due to interferences caused by laborious immobilization and stimulus delivery procedures. Here, we have developed an automated microfluidic platform that is capable of trapping more than 500 single cells into microwells with a loading efficiency of 77% within two minutes, delivering multiple chemical stimuli and performing calcium imaging with enhanced spatial and temporal resolutions when compared to bath perfusion systems. Results revealed the presence of heterogeneity in cellular responses to the type, concentration, and order of applied sweet and bitter stimuli. Sucralose and denatonium benzoate elicited robust increases in the intracellular Ca2+ concentration. However, glucose evoked a rapid elevation of intracellular Ca2+ followed by reduced responses to subsequent glucose stimulation. Using Gymnema sylvestre as a blocking agent for the sweet taste receptor confirmed that different taste receptors were utilized for sweet and bitter tastes. This automated microfluidic platform is cost-effective, easy to fabricate and operate, and may be generally applicable for high-throughput and high-content single-cell analysis and drug screening. [ABSTRACT FROM AUTHOR]