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Dibattista M, Pifferi S, Hernandez-Clavijo A, Menini A. The physiological roles of anoctamin2/TMEM16B and anoctamin1/TMEM16A in chemical senses. Cell Calcium 2024; 120:102889. [PMID: 38677213 DOI: 10.1016/j.ceca.2024.102889] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2024] [Revised: 04/11/2024] [Accepted: 04/17/2024] [Indexed: 04/29/2024]
Abstract
Chemical senses allow animals to detect and discriminate a vast array of molecules. The olfactory system is responsible of the detection of small volatile molecules, while water dissolved molecules are detected by taste buds in the oral cavity. Moreover, many animals respond to signaling molecules such as pheromones and other semiochemicals through the vomeronasal organ. The peripheral organs dedicated to chemical detection convert chemical signals into perceivable information through the employment of diverse receptor types and the activation of multiple ion channels. Two ion channels, TMEM16B, also known as anoctamin2 (ANO2) and TMEM16A, or anoctamin1 (ANO1), encoding for Ca2+-activated Cl¯ channels, have been recently described playing critical roles in various cell types. This review aims to discuss the main properties of TMEM16A and TMEM16B-mediated currents and their physiological roles in chemical senses. In olfactory sensory neurons, TMEM16B contributes to amplify the odorant response, to modulate firing, response kinetics and adaptation. TMEM16A and TMEM16B shape the pattern of action potentials in vomeronasal sensory neurons increasing the interspike interval. In type I taste bud cells, TMEM16A is activated during paracrine signaling mediated by ATP. This review aims to shed light on the regulation of diverse signaling mechanisms and neuronal excitability mediated by Ca-activated Cl¯ channels, hinting at potential new roles for TMEM16A and TMEM16B in the chemical senses.
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Affiliation(s)
- Michele Dibattista
- Department of Translational Biomedicine and Neuroscience, University of Bari A. Moro, 70121 Bari, Italy
| | - Simone Pifferi
- Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, 60126 Ancona, Italy.
| | - Andres Hernandez-Clavijo
- Department of Chemosensation, Institute for Biology II, RWTH Aachen University, 52074 Aachen, Germany
| | - Anna Menini
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, 34136 Trieste, Italy.
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Guarascio DM, Gonzalez-Velandia KY, Hernandez-Clavijo A, Menini A, Pifferi S. Functional expression of TMEM16A in taste bud cells. J Physiol 2021; 599:3697-3714. [PMID: 34089532 PMCID: PMC8361675 DOI: 10.1113/jp281645] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2021] [Accepted: 06/04/2021] [Indexed: 12/14/2022] Open
Abstract
Key points Taste transduction occurs in taste buds in the tongue epithelium. The Ca2+‐activated Cl– channels TMEM16A and TMEM16B play relevant physiological roles in several sensory systems. Here, we report that TMEM16A, but not TMEM16B, is expressed in the apical part of taste buds. Large Ca2+‐activated Cl− currents blocked by Ani‐9, a selective inhibitor of TMEM16A, are measured in type I taste cells but not in type II or III taste cells. ATP indirectly activates Ca2+‐activated Cl– currents in type I cells through TMEM16A channels. These results indicate that TMEM16A is functional in type I taste cells and contribute to understanding the largely unknown physiological roles of these cells.
Abstract The Ca2+‐activated Cl– channels TMEM16A and TMEM16B have relevant roles in many physiological processes including neuronal excitability and regulation of Cl– homeostasis. Here, we examined the presence of Ca2+‐activated Cl– channels in taste cells of mouse vallate papillae by using immunohistochemistry and electrophysiological recordings. By using immunohistochemistry we showed that only TMEM16A, and not TMEM16B, was expressed in taste bud cells where it largely co‐localized with the inwardly rectifying K+ channel KNCJ1 in the apical part of type I cells. By using whole‐cell patch‐clamp recordings in isolated cells from taste buds, we measured an average current of −1083 pA at −100 mV in 1.5 μm Ca2+ and symmetrical Cl– in type I cells. Ion substitution experiments and blockage by Ani‐9, a specific TMEM16A channel blocker, indicated that Ca2+ activated anionic currents through TMEM16A channels. We did not detect any Ca2+‐activated Cl– currents in type II or III taste cells. ATP is released by type II cells in response to various tastants and reaches type I cells where it is hydrolysed by ecto‐ATPases. Type I cells also express P2Y purinergic receptors and stimulation of type I cells with extracellular ATP produced large Ca2+‐activated Cl− currents blocked by Ani‐9, indicating a possible role of TMEM16A in ATP‐mediated signalling. These results provide a definitive demonstration that TMEM16A‐mediated currents are functional in type I taste cells and provide a foundation for future studies investigating physiological roles for these often‐neglected taste cells. Taste transduction occurs in taste buds in the tongue epithelium. The Ca2+‐activated Cl– channels TMEM16A and TMEM16B play relevant physiological roles in several sensory systems. Here, we report that TMEM16A, but not TMEM16B, is expressed in the apical part of taste buds. Large Ca2+‐activated Cl− currents blocked by Ani‐9, a selective inhibitor of TMEM16A, are measured in type I taste cells but not in type II or III taste cells. ATP indirectly activates Ca2+‐activated Cl– currents in type I cells through TMEM16A channels. These results indicate that TMEM16A is functional in type I taste cells and contribute to understanding the largely unknown physiological roles of these cells.
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Affiliation(s)
- Domenico M Guarascio
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, 34136, Italy
| | | | - Andres Hernandez-Clavijo
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, 34136, Italy
| | - Anna Menini
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, 34136, Italy
| | - Simone Pifferi
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, 34136, Italy.,Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, 60126, Italy
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Sparks JT, Botsko G, Swale DR, Boland LM, Patel SS, Dickens JC. Membrane Proteins Mediating Reception and Transduction in Chemosensory Neurons in Mosquitoes. Front Physiol 2018; 9:1309. [PMID: 30294282 PMCID: PMC6158332 DOI: 10.3389/fphys.2018.01309] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 08/30/2018] [Indexed: 12/17/2022] Open
Abstract
Mosquitoes use chemical cues to modulate important behaviors such as feeding, mating, and egg laying. The primary chemosensory organs comprising the paired antennae, maxillary palps and labial palps are adorned with porous sensilla that house primary sensory neurons. Dendrites of these neurons provide an interface between the chemical environment and higher order neuronal processing. Diverse proteins located on outer membranes interact with chemicals, ions, and soluble proteins outside the cell and within the lumen of sensilla. Here, we review the repertoire of chemosensory receptors and other membrane proteins involved in transduction and discuss the outlook for their functional characterization. We also provide a brief overview of select ion channels, their role in mammalian taste, and potential involvement in mosquito taste. These chemosensory proteins represent targets for the disruption of harmful biting behavior and disease transmission by mosquito vectors.
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Affiliation(s)
- Jackson T Sparks
- Biology Department, High Point University, High Point, NC, United States
| | - Gina Botsko
- Biology Department, High Point University, High Point, NC, United States
| | - Daniel R Swale
- Department of Entomology, Louisiana State University AgCenter, Baton Rouge, LA, United States
| | - Linda M Boland
- Department of Biology, University of Richmond, Richmond, VA, United States
| | - Shriraj S Patel
- Department of Biology, University of Richmond, Richmond, VA, United States
| | - Joseph C Dickens
- Department of Biology, University of Richmond, Richmond, VA, United States
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Recent Advances in Molecular Mechanisms of Taste Signaling and Modifying. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2016; 323:71-106. [PMID: 26944619 DOI: 10.1016/bs.ircmb.2015.12.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The sense of taste conveys crucial information about the quality and nutritional value of foods before it is ingested. Taste signaling begins with taste cells via taste receptors in oral cavity. Activation of these receptors drives the transduction systems in taste receptor cells. Then particular transmitters are released from the taste cells and activate corresponding afferent gustatory nerve fibers. Recent studies have revealed that taste sensitivities are defined by distinct taste receptors and modulated by endogenous humoral factors in a specific group of taste cells. Such peripheral taste generations and modifications would directly influence intake of nutritive substances. This review will highlight current understanding of molecular mechanisms for taste reception, signal transduction in taste bud cells, transmission between taste cells and nerves, regeneration from taste stem cells, and modification by humoral factors at peripheral taste organs.
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Ileri-Gurel E, Pehlivanoglu B, Dogan M. Effect of Acute Stress on Taste Perception: In Relation with Baseline Anxiety Level and Body Weight. Chem Senses 2012; 38:27-34. [DOI: 10.1093/chemse/bjs075] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
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Dye-permeable, voltage-gated channel on mouse fungiform taste bud cells. Brain Res 2010; 1373:17-24. [PMID: 21167135 DOI: 10.1016/j.brainres.2010.12.019] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2010] [Revised: 12/07/2010] [Accepted: 12/08/2010] [Indexed: 11/20/2022]
Abstract
We show here the expression, permeability and pharmacology of a voltage-gated channel in certain taste bud cells (TBCs) which is known to be permeable to Lucifer Yellow CH (LY) and known to release ATP as a neurotransmitter in response to taste substances. LY dissolved in a 200 mM K(+)-containing solution label TBCs immunoreactive to PLCβ2, a phospholipase subtype, but not the TBC subtype immunoreactive to SNAP-25, a SNARE protein. In addition to these subtypes, LY also labelled a few of the non-immunoreactive TBCs. Monovalent and divalent anion probes with molar mass less than 1200 also label PLCβ2-immunoreactive TBCs and a few non-immunoreactive TBCs, whereas a cation probe, rhodamine B, labels the cell membrane of TBCs nonselectively and K(+) independently. The number of LY-labelled TBCs is decreased by 5 μM DIDS (4,4'-diisothiocyanostilbene-2-2'disulfonate), 1mM octanol and 10(-5)M H(+), but not by 10 μM carbenoxolone, 2mM probenecid, 10mM TEA, or 30 μM flufenamic acid. PLCβ2-immunoreactive TBCs and a few non-immunoreactive TBCs generate a TEA-insensitive outwardly rectifying current. DIDS decreases this current in magnitude with IC(50) of ~0.4 μM in a voltage-independent manner. Also 10(-5)M H(+) and 1mM octanol decreases the current magnitude, but 10 μM carbenoxolone and 2mM probenecid do not. These results show that the LY-permeable channel preferably permeates anions and occurs not only on PLCβ2-immunoreactive TBCs but also on certain non-immunoreactive TBCs. Also the results show that the pharmacology of the LY-permeable channel is different from hemichannels reported. The discussion focuses on the pharmacology and the role of the LY-permeable channel.
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7
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Zhang Y, Kolli T, Hivley R, Jaber L, Zhao FI, Yan J, Herness S. Characterization of the expression pattern of adrenergic receptors in rat taste buds. Neuroscience 2010; 169:1421-37. [PMID: 20478367 DOI: 10.1016/j.neuroscience.2010.05.021] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2010] [Revised: 05/03/2010] [Accepted: 05/11/2010] [Indexed: 12/01/2022]
Abstract
Taste buds signal the presence of chemical stimuli in the oral cavity to the central nervous system using both early transduction mechanisms, which allow single cells to be depolarized via receptor-mediated signaling pathways, and late transduction mechanisms, which involve extensive cell-to-cell communication among the cells in the bud. The latter mechanisms, which involve a large number of neurotransmitters and neuropeptides, are less well understood. Among neurotransmitters, multiple lines of evidence suggest that norepinephrine plays a yet unknown role in the taste bud. This study investigated the expression pattern of adrenergic receptors in the rat posterior taste bud. Expression of alpha1A, alpha1B, alpha1D, alpha2A, alpha2B, alpha2C, beta1, and the beta2 adrenoceptor subtypes was observed in taste buds using RT-PCR and immunocytochemical techniques. Taste buds also expressed the biosynthetic enzyme for norepinephrine, dopamine beta-hydroxylase (DbetaH), as well as the norepinephrine transporter. Further, expression of the epinephrine synthetic enzyme, phenylethanolamine N-methyltransferase (PNMT), was observed suggesting a possible role for this transmitter in the bud. Phenotyping adrenoceptor expression patterns with double labeling experiments to gustducin, synaptosomal-associated protein 25 (SNAP-25), and neural cell adhesion molecule (NCAM) suggests they are prominently expressed in subsets of cells known to express taste receptor molecules but segregated from cells known to have synapses with the afferent nerve fiber. Alpha and beta adrenoceptors co-express with one another in unique patterns as observed with immunocytochemistry and single cell reverse transcription polymerase chain reaction (RT-PCR). These data suggest that single cells express multiple adrenergic receptors and that adrenergic signaling may be particularly important in bitter, sweet, and umami taste qualities. In summary, adrenergic signaling in the taste bud occurs through complex pathways that include presynaptic and postsynaptic receptors and likely play modulatory roles in processing of gustatory information similar to other peripheral sensory systems such as the retina, cochlea, and olfactory bulb.
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Affiliation(s)
- Y Zhang
- Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, School of Medicine, Xi'an Jiaotong University, 76# West Yanta Road, Xi'an 710061, PR China
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Moyer BD, Hevezi P, Gao N, Lu M, Kalabat D, Soto H, Echeverri F, Laita B, Yeh SA, Zoller M, Zlotnik A. Expression of genes encoding multi-transmembrane proteins in specific primate taste cell populations. PLoS One 2009; 4:e7682. [PMID: 19997627 PMCID: PMC2780358 DOI: 10.1371/journal.pone.0007682] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2009] [Accepted: 10/08/2009] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND Using fungiform (FG) and circumvallate (CV) taste buds isolated by laser capture microdissection and analyzed using gene arrays, we previously constructed a comprehensive database of gene expression in primates, which revealed over 2,300 taste bud-associated genes. Bioinformatics analyses identified hundreds of genes predicted to encode multi-transmembrane domain proteins with no previous association with taste function. A first step in elucidating the roles these gene products play in gustation is to identify the specific taste cell types in which they are expressed. METHODOLOGY/PRINCIPAL FINDINGS Using double label in situ hybridization analyses, we identified seven new genes expressed in specific taste cell types, including sweet, bitter, and umami cells (TRPM5-positive), sour cells (PKD2L1-positive), as well as other taste cell populations. Transmembrane protein 44 (TMEM44), a protein with seven predicted transmembrane domains with no homology to GPCRs, is expressed in a TRPM5-negative and PKD2L1-negative population that is enriched in the bottom portion of taste buds and may represent developmentally immature taste cells. Calcium homeostasis modulator 1 (CALHM1), a component of a novel calcium channel, along with family members CALHM2 and CALHM3; multiple C2 domains; transmembrane 1 (MCTP1), a calcium-binding transmembrane protein; and anoctamin 7 (ANO7), a member of the recently identified calcium-gated chloride channel family, are all expressed in TRPM5 cells. These proteins may modulate and effect calcium signalling stemming from sweet, bitter, and umami receptor activation. Synaptic vesicle glycoprotein 2B (SV2B), a regulator of synaptic vesicle exocytosis, is expressed in PKD2L1 cells, suggesting that this taste cell population transmits tastant information to gustatory afferent nerve fibers via exocytic neurotransmitter release. CONCLUSIONS/SIGNIFICANCE Identification of genes encoding multi-transmembrane domain proteins expressed in primate taste buds provides new insights into the processes of taste cell development, signal transduction, and information coding. Discrete taste cell populations exhibit highly specific gene expression patterns, supporting a model whereby each mature taste receptor cell is responsible for sensing, transmitting, and coding a specific taste quality.
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Affiliation(s)
- Bryan D Moyer
- Senomyx, Inc, San Diego, California, United States of America.
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Formaker BK, Lin H, Hettinger TP, Frank ME. Responses of the hamster chorda tympani nerve to sucrose+acid and sucrose+citrate taste mixtures. Chem Senses 2009; 34:607-16. [PMID: 19620386 PMCID: PMC2728834 DOI: 10.1093/chemse/bjp043] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Studies of taste receptor cells, chorda tympani (CT) neurons, and brainstem neurons show stimulus interactions in the form of inhibition or enhancement of the effectiveness of sucrose when mixed with acids or citrate salts, respectively. To investigate further the effects of acids and the trivalent citrate anion on sucrose responses in hamsters (Mesocricetus auratus), we recorded multifiber CT responses to 100 mM sucrose; a concentration series of HCl, citric acid, acetic acid, sodium citrate (with and without amiloride added), potassium citrate, and all binary combinations of acids and salts with 100 mM sucrose. Compared with response additivity, sucrose responses were increasingly suppressed in acid + sucrose mixtures with increases in titratable acidity, but HCl and citric acid were more effective suppressors than acetic acid. Citrate salts suppressed sucrose responses and baseline CT neural activity to a similar degree. Citrate salts also elicited prolonged, concentration-dependent, water-rinse responses. The specific loss in sucrose effectiveness as a CT stimulus with increasing titratable acidity was confirmed; however, no increase in sucrose effectiveness was found with the addition of citrate. Further study is needed to define the chemical basis for effects of acids and salts in taste mixtures.
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Affiliation(s)
- Bradley K Formaker
- Department of Oral Health and Diagnostic Sciences, School of Dental Medicine, University of Connecticut Health Center, Farmington, CT 06030, USA.
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The neuropeptides CCK and NPY and the changing view of cell-to-cell communication in the taste bud. Physiol Behav 2009; 97:581-91. [PMID: 19332083 DOI: 10.1016/j.physbeh.2009.02.043] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2008] [Accepted: 02/16/2009] [Indexed: 11/24/2022]
Abstract
The evolving view of the taste bud increasingly suggests that it operates as a complex signal processing unit. A number of neurotransmitters and neuropeptides and their corresponding receptors are now known to be expressed in subsets of taste receptor cells in the mammalian bud. These expression patterns set up hard-wired cell-to-cell communication pathways whose exact physiological roles still remain obscure. As occurs in other cellular systems, it is likely that neuropeptides are co-expressed with neurotransmitters and function as neuromodulators. Several neuropeptides have been identified in taste receptor cells including cholecystokinin (CCK), neuropeptide Y (NPY), vasoactive intestinal peptide (VIP), and glucagon-like peptide 1 (GLP-1). Of these, CCK and NPY are the best studied. These two peptides are co-expressed in the same presynaptic cells; however, their postsynaptic actions are both divergent and antagonistic. CCK and its receptor, the CCK-1 subtype, are expressed in the same subset of taste receptor cells and the autocrine activation of these cells produces a number of excitatory physiological actions. Further, most of these cells are responsive to bitter stimuli. On the other hand, NPY and its receptor, the NPY-1 subtype, are expressed in different cells. NPY, acting in a paracrine fashion on NPY-1 receptors, results in inhibitory actions on the cell. Preliminary evidence suggests the NPY-1 receptor expressing cell co-expresses T1R3, a member of the T1R family of G-protein coupled receptors thought to be important in detection of sweet and umami stimuli. Thus the neuropeptide expressing cells co-express CCK, NPY, and CCK-1 receptor. Neuropeptides released from these cells during bitter stimulation may work in concert to both modulate the excitation of bitter-sensitive taste receptor cells while concurrently inhibiting sweet-sensitive cells. This modulatory process is similar to the phenomenon of lateral inhibition that occurs in other sensory systems.
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GABA expression in the mammalian taste bud functions as a route of inhibitory cell-to-cell communication. Proc Natl Acad Sci U S A 2009; 106:4006-11. [PMID: 19223578 DOI: 10.1073/pnas.0808672106] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recent advances have underscored cell-to-cell communication as an important component of the operation of taste buds with individual taste receptor cells (TRCs) communicating with one another by means of a number of neurotransmitters and neuropeptides, although functional roles are not yet understood. Here, we characterize the presence, distribution pattern, phenotype, and functional consequences of a previously undescribed inhibitory route within the taste bud mediated by the classic neurotransmitter GABA and its receptors. By using immunocytochemistry, subsets of TRCs within rat taste buds were identified as expressing GABA, and its synthetic enzyme glutamate decarboxylase (GAD). GAD expression was verified with Western blotting. Immunofluorescent studies revealed complex coexpression patterns of GAD with the TRC protein markers gustducin, neural cell adhesion molecule, protein gene product 9.5, and synaptosomal-associated protein of 25 kDa that collectively outline hardwired signaling pathways of GABAergic TRCs. RT-PCR and immunocytochemistry demonstrated that both GABA(A) and GABA(B) receptors are expressed in the taste bud. The later was observed in a subset TRCs paracrine to GAD-expressing TRCs. Physiological effects of GABA were examined by patch clamp recordings. GABA and the GABA(A) agonists muscimol and isoguvacine enhanced isolated chloride currents in a dose-dependent manner. Also, GABA and the GABA(B) agonist baclofen both elicited increases of the inwardly rectifying potassium currents that could be blocked by the GABA(B) receptor antagonist CGP 35348 and the G protein blocker GDP-betaS. Collectively, these data suggest that GABAergic TRCs are able to shape the final chemosensory output of the bud by means of processes of cell-to-cell modulation.
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Abstract
ATP and serotonin (5-HT) are neurotransmitters secreted from taste bud receptor (type II) and presynaptic (type III) cells, respectively. Norepinephrine (NE) has also been proposed to be a neurotransmitter or paracrine hormone in taste buds. Yet, to date, the specific stimulus for NE release in taste buds is not well understood, and the identity of the taste cells that secrete NE is not known. Chinese hamster ovary cells were transfected with alpha(1A) adrenoceptors and loaded with fura-2 ("biosensors") to detect NE secreted from isolated mouse taste buds and taste cells. Biosensors responded to low concentrations of NE (>or=10 nm) with a reliable fura-2 signal. NE biosensors did not respond to stimulation with KCl or taste compounds. However, we recorded robust responses from NE biosensors when they were positioned against mouse circumvallate taste buds and the taste buds were stimulated with KCl (50 mm) or a mixture of taste compounds (cycloheximide, 10 microm; saccharin, 2 mm; denatonium, 1 mm; SC45647, 100 microm). NE biosensor responses evoked by stimulating taste buds were reversibly blocked by prazosin, an alpha(1A) receptor antagonist. Together, these findings indicate that taste bud cells secrete NE when they are stimulated. We isolated individual taste bud cells to identify the origin of NE release. NE was secreted only from presynaptic (type III) taste cells and not receptor (type II) cells. Stimulus-evoked NE release depended on Ca(2+) in the bathing medium. Using dual biosensors (sensitive to 5-HT and NE), we found all presynaptic cells secrete 5-HT and 33% corelease NE with 5-HT.
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Merigo F, Benati D, Galie M, Crescimanno C, Osculati F, Sbarbati A. Immunohistochemical Localization of Cystic Fibrosis Transmembrane Regulator and Clara Cell Secretory Protein in Taste Receptor Cells of Rat Circumvallate Papillae. Chem Senses 2007; 33:231-41. [DOI: 10.1093/chemse/bjm082] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
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Ando H, Tomida M, Inoue K, Asanuma N. Dopamine beta-hydroxylase like immunoreactive cells in the frog taste disc. Chem Senses 2007; 32:825-32. [PMID: 17693417 DOI: 10.1093/chemse/bjm051] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We immunohistochemically examined the existence of dopamine beta-hydroxylase (DBH), a noradrenalin (NA)-synthesizing enzyme from dopamine, in the taste disc of frog, Rana catesbeiana. DBH-like immunoreactive cells were located in the intermediate layer in the taste disc; the cells showed an apical process reaching the surface of the disc and one or several basal processes. Cells with a thick apical process and those with a thin apical process were both immunoreactive: these cells corresponded to type II and III receptor cells of the frog taste disc. Immunoreactive granules were observed in the cytoplasm of those cells. In the frog taste disc, only type III cells are reported to have afferent synapses with the nerve via basal processes but those basal processes have not been reported in type II cells. In the present study, we found that type II-like cells possessed a long basal process extending toward the basal lamina. Mucous (type Ia) cells, wing (type Ib) cells, and glia-like sustentacular (type Ic) cells were all immunohistochemically unreactive. The present observations support the argument that NA (or adrenalin) may work as a chemical transmitter in the frog taste organ.
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Affiliation(s)
- Hiroshi Ando
- Department of Oral Physiology, Matsumoto Dental University School of Dentistry, Shiojiri, Japan.
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Hodson NA, Linden RWA. The effect of monosodium glutamate on parotid salivary flow in comparison to the response to representatives of the other four basic tastes. Physiol Behav 2006; 89:711-7. [PMID: 17028046 DOI: 10.1016/j.physbeh.2006.08.011] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2005] [Revised: 02/26/2006] [Accepted: 08/10/2006] [Indexed: 11/18/2022]
Abstract
Parotid salivary flow was recorded from eight fit and healthy subjects using modified Lashley cups connected to an instantaneous flow meter in response to gustatory stimuli. The gustatory stimuli were monosodium glutamate (MSG), sodium chloride, sucrose, magnesium sulphate and citric acid. Stimuli were applied for 30 s, and repeated after the flows had returned to baseline following the rinse. Subjects were a significant source of variation for salivary response to each different test stimuli (p<0.001). The normalised salivary flow showed a strong correlation to concentration for all test stimuli (p<0.0001). The parotid salivary flow to MSG (umami) showed a dose-dependant response in which both Na(+) and glutamate ions contributed. The overall order of relative salivary flow responses from highest to lowest flows was citric acid (sour)>MSG (umami)>NaCl (salt)>sucrose (sweet)>=magnesium sulphate (bitter). The relative responses of the peak salivary flows showed the same ordered relation. The peak salivary flow provided a greater contribution to the response to citric acid, NaCl and MSG compared to the response to sucrose and magnesium sulphate.
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Affiliation(s)
- N A Hodson
- Primary Dental Care, King's College London Dental Institute at Guy's, King's and St Thomas' Hospitals, London SE5 9RW, UK.
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Huang L, Cao J, Wang H, Vo LA, Brand JG. Identification and functional characterization of a voltage-gated chloride channel and its novel splice variant in taste bud cells. J Biol Chem 2005; 280:36150-7. [PMID: 16129671 PMCID: PMC2367165 DOI: 10.1074/jbc.m507706200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Taste bud cells are epithelial cells with neuronal properties. Voltage-dependent ion channels have been physiologically described in these cells. Here, we report the molecular identification and functional characterization of a voltage-gated chloride channel (ClC-4) and its novel splice variant (ClC-4A) from taste bud cells. ClC-4A skipped an exon near its 5'-end, incurring the loss of 60 amino acids at the N terminus. In situ hybridization and immunohistochemistry localized these two channels' transcripts and proteins to a subset of taste bud cells. Electrophysiological recordings of the heterologously expressed channels in Xenopus oocytes showed that ClC-4 and ClC-4A have opposite sensitivity to pH and unique ion selectivity. The chloride channel blockers niflumic acid and 5-nitro-2-(3-phenylpropylamino)benzoic acid had a slight or no inhibitory effect on the conductance of ClC-4, but both blockers inhibited ClC-4A, suggesting that ClC-4A is a candidate channel for an acid-induced 5-nitro-2-(3-phenylpropylamino)benzoic acid-sensitive current. Furthermore, these two channels may play a role in bitter-, sweet-, and umami-mediated taste transmission by regulating transmitter uptake into synaptic vesicles.
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Affiliation(s)
- Liquan Huang
- Monell Chemical Senses Center, Philadelphia, Pennsylvania 19104-3308, USA.
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17
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Zhao FL, Shen T, Kaya N, Lu SG, Cao Y, Herness S. Expression, physiological action, and coexpression patterns of neuropeptide Y in rat taste-bud cells. Proc Natl Acad Sci U S A 2005; 102:11100-5. [PMID: 16040808 PMCID: PMC1182420 DOI: 10.1073/pnas.0501988102] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Recent studies have suggested that neuropeptides could play previously unrecognized functional roles in peripheral gustation. To date, two peptides, cholecystokinin and vasoactive intestinal peptide, have been localized to subsets of taste-bud (TB) cells (TBC) and one, cholecystokinin, has been demonstrated to produce excitatory physiological actions. This study extends our knowledge of neuropeptides in TBC in three significant ways. First, using techniques of immunocytochemistry and RT-PCR, evidence is presented for the expression of a third peptide, neuropeptide Y (NPY). Like other peptide expression patterns, NPY expression is circumscribed to a subset of cells within the taste bud. Second, using physiological studies, we demonstrate that NPY specifically enhances an inwardly rectifying potassium current via NPY-Y1 receptors. This action is antagonistic to the previously demonstrated inhibitory effect exerted by cholecystokinin on the same current, thus providing important clues to their signaling roles in the TB. Third, using the technique of double-labeled fluorescent immunocytochemistry, the relationship of three subsets of neuropeptide-expressing TB cells to one another was examined. Remarkably, NPY expressions, although fewer in number than either the cholecystokinin or vasoactive intestinal peptide subsets, overlapped 100% with either peptide. Collectively, these three observations transform previously suggestive roles of neuromodulation by peptides in TB cells to more concrete signaling pathways. The extensive colocalization of these peptides suggests they may be subject to similar presynaptic influences of release yet have antagonistic postsynaptic actions. The convergence or divergence of these postsynaptic actions awaits further investigation.
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Affiliation(s)
- Fang-li Zhao
- College of Dentistry, Ohio State University, 305 West 12th Street, 108 North Greene Street, Columbus, OH 43210, USA
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18
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Abstract
Calcium-activated chloride channels (CaCCs) play important roles in cellular physiology, including epithelial secretion of electrolytes and water, sensory transduction, regulation of neuronal and cardiac excitability, and regulation of vascular tone. This review discusses the physiological roles of these channels, their mechanisms of regulation and activation, and the mechanisms of anion selectivity and conduction. Despite the fact that CaCCs are so broadly expressed in cells and play such important functions, understanding these channels has been limited by the absence of specific blockers and the fact that the molecular identities of CaCCs remains in question. Recent status of the pharmacology and molecular identification of CaCCs is evaluated.
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Affiliation(s)
- Criss Hartzell
- Department of Cell Biology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
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19
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Ghiaroni V, Sasaki M, Fuwa H, Rossini GP, Scalera G, Yasumoto T, Pietra P, Bigiani A. Inhibition of Voltage-Gated Potassium Currents by Gambierol in Mouse Taste Cells. Toxicol Sci 2005; 85:657-65. [PMID: 15689421 DOI: 10.1093/toxsci/kfi097] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Ciguatera is a food poisoning caused by toxins of Gambierdiscus toxicus, a marine dinoflagellate. The neurological features of this intoxication include sensory abnormalities, such as paraesthesia, heightened nociperception, and also taste alterations. Here, we have evaluated the effect of gambierol, one of the possible ciguatera toxins, on the voltage-gated ion currents in taste cells. Taste cells are excitable cells endowed with voltage-gated Na+, K+, and Cl- currents (I(Na), I(K), and I(Cl), respectively). By applying the patch-clamp technique to single cells in isolated taste buds obtained from the mouse vallate papilla, we have recorded such currents and determined the effect of bath-applied gambierol. We found that this toxin markedly inhibited I(K) in the nanomolar range (IC50 of 1.8 nM), whereas it showed no significant effect on I(Na) or I(Cl) even at high concentration (1 microM). The block of I(K) was irreversible even after a 50-min wash. In addition to affecting the current amplitude, we found that gambierol significantly altered both the activation and inactivation processes of I(K). In conclusion, unlike other toxins involved in ciguatera, such as ciguatoxins, which affect the functioning of voltage-gated sodium channels, the preferred molecular target of gambierol is the voltage-gated potassium channel, at least in taste cells. Voltage-gated potassium currents play an important role in the generation of the firing pattern during chemotransduction. Thus, gambierol may alter action potential discharge in taste cells and this could be associated with the taste alterations reported in the clinical literature.
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Affiliation(s)
- Valeria Ghiaroni
- Dipartimento di Scienze Biomediche, Università di Modena e Reggio Emilia, 41100 Modena, Italy
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20
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Shen T, Kaya N, Zhao FL, Lu SG, Cao Y, Herness S. Co-expression patterns of the neuropeptides vasoactive intestinal peptide and cholecystokinin with the transduction molecules α-gustducin and T1R2 in rat taste receptor cells. Neuroscience 2005; 130:229-38. [PMID: 15561439 DOI: 10.1016/j.neuroscience.2004.09.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/01/2004] [Indexed: 10/26/2022]
Abstract
Taste receptor cells are primary sensory receptors utilized by the nervous system to detect the presence of gustatory stimuli in the oral cavity. These cells are particularly heterogeneous and may be divided into various subtypes based on morphological, histochemical, or physiological criteria. One example is the heterogeneous expression of neuropeptides, such as cholecystokinin and vasoactive intestinal polypeptide. These peptides are hypothesized to participate in the transduction processes. To pursue examination of this hypothesis, this study explored the relationship of peptide expression with two important and mostly non-overlapping transductive elements--the taste-specific G protein gustducin, involved in bitter and sweet transduction cascades, and the seven transmembrane taste receptor T1R2, hypothesized to respond to sweet compounds. Double labeling experiments were performed on taste buds of the posterior rat tongue combining immunocytochemistry for peptide expression and in situ hybridization experiments for either gustducin or T1R2 expression. Additionally, vasoactive intestinal peptide (VIP)-expression in posterior taste receptor cells was confirmed using the technique of RT-PCR. More than half (56%) of the CCK-expressing taste receptor cells co-expressed alpha-gustducin mRNA whereas far fewer (15%) co-expressed T1R2 mRNA. A majority of VIP-expressing taste receptor cells co-expressed alpha-gustducin mRNA (60%) whereas only 19% of these cells co-expressed T1R2 mRNA. More remarkable was the observation that these two peptides displayed almost identical expression patterns with these signal transduction molecules, suggesting that peptides are not randomly expressed with relation to signal transduction molecules. This observation supports the hypothesis that peptides may play roles in transduction. Further physiological exploration will be required to elucidate the nature of these roles.
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Affiliation(s)
- T Shen
- Section of Oral Biology, College of Dentistry, Ohio State University, 305 West 12th Avenue, Columbus, OH 43210, USA
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21
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Kaya N, Shen T, Lu SG, Zhao FL, Herness S. A paracrine signaling role for serotonin in rat taste buds: expression and localization of serotonin receptor subtypes. Am J Physiol Regul Integr Comp Physiol 2004; 286:R649-58. [PMID: 14715493 DOI: 10.1152/ajpregu.00572.2003] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Recent advances in peripheral taste physiology now suggest that the classic linear view of information processing within the taste bud is inadequate and that paracrine processing, although undemonstrated, may be an essential feature of peripheral gustatory transduction. Taste receptor cells (TRCs) express multiple neurotransmitters of unknown function that could potentially participate in a paracrine role. Serotonin is expressed in a subset of TRCs with afferent synapses; additionally, TRCs respond physiologically to serotonin. This study explored the expression and cellular localization of serotonin receptor subtypes in TRCs as a possible route of paracrine communication. RT-PCR was performed on RNA extracted from rat posterior taste buds with 14 primer sets representing 5-HT1 through 5-HT7 receptor subtype families. Data suggest that 5-HT1A and 5-HT3 receptors are expressed in taste buds. Immunocytochemistry with a 5-HT1A-specific antibody demonstrated that subsets of TRCs were immunopositive for 5-HT1A. With the use of double-labeling, serotonin- and 5-HT1A-immunopositive cells were observed exclusively in nonoverlapping populations. On the other hand, 5-HT3-immunopositive taste receptor cells were not observed. This observation, combined with other data, suggests 5-HT3 is expressed in postsynaptic neural elements within the bud. We hypothesize that 5-HT release from TRCs activates postsynaptic 5-HT3 receptors on afferent nerve fibers and, via a paracrine route, inhibits neighboring TRCs via 5-HT1A receptors. The role of the 5-HT1A-expressing TRC within the taste bud remains to be explored.
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MESH Headings
- Animals
- Electrophoresis, Polyacrylamide Gel
- Fluorescent Antibody Technique
- Immunohistochemistry
- Male
- Paracrine Communication/physiology
- RNA/analysis
- RNA/biosynthesis
- Rats
- Rats, Sprague-Dawley
- Receptor, Serotonin, 5-HT1A/biosynthesis
- Receptor, Serotonin, 5-HT1A/physiology
- Receptors, Serotonin/biosynthesis
- Receptors, Serotonin/physiology
- Receptors, Serotonin, 5-HT3/biosynthesis
- Receptors, Serotonin, 5-HT3/physiology
- Reverse Transcriptase Polymerase Chain Reaction
- Serotonin/physiology
- Signal Transduction/physiology
- Spectrophotometry, Ultraviolet
- Taste Buds/metabolism
- Taste Buds/physiology
- Tissue Fixation
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Affiliation(s)
- Namik Kaya
- College of Dentistry, The Ohio State University, 305 West 12th Ave., Columbus, OH 43210, USA
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22
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Baryshnikov SG, Rogachevskaja OA, Kolesnikov SS. Calcium signaling mediated by P2Y receptors in mouse taste cells. J Neurophysiol 2003; 90:3283-94. [PMID: 12878712 DOI: 10.1152/jn.00312.2003] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Evidence implicates a number of neuroactive substances and their receptors in mediating complex cell-to-cell communications in the taste bud. Recently, we found that ATP, a ubiquitous neurotransmitter/neuromodulator, mobilizes intracellular Ca2+ in taste cells by activating P2Y receptors. Here, P2Y receptor-cellular response coupling was characterized in detail using single cell ratio photometry and the inhibitory analysis. The sequence of underlying events was shown to include ATP-dependent activation of PLC, IP3 production, and IP3 receptor-mediated Ca2+ release followed by Ca2+ influx. Data obtained favor SOC channels rather than receptor-operated channels as a pathway for Ca2+ influx that accompanies Ca2+ release. Intracellular Ca2+ mobilized by ATP is apparently extruded by the plasma membrane Ca2+-ATPase, while a contribution of the Na+/Ca2+ exchange and other mechanisms of Ca2+ clearance is negligible. Cyclic AMP-dependent phosphorylation is likely to control a gain of the phosphoinositide cascade involved in ATP transduction. ATP-responsive taste cells are abundant in circumvallate, foliate, and fungiform papillae. Taken together, our observations point to a putative role for ATP as a neurotransmitter operative in the taste bud.
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Affiliation(s)
- Sergey G Baryshnikov
- Institute of Cell Biophysics, Russian Academy of Sciences, Pushchino, Moscow Region, 142290, Russia
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23
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Noguchi T, Ikeda Y, Miyajima M, Yoshii K. Voltage-gated channels involved in taste responses and characterizing taste bud cells in mouse soft palates. Brain Res 2003; 982:241-59. [PMID: 12915259 DOI: 10.1016/s0006-8993(03)03013-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Taste bud cells (TBCs) on soft palates differ from those on tongues in innervation and chemosensitivity. We investigated voltage-gated channels involved in the taste responses of TBCs on mouse soft palates under in-situ tight-seal voltage/current-clamp conditions. Under the cell-attached mode, TBCs spontaneously fired action currents, which were blocked by application of 1 microM TTX to TBC basolateral membranes. Firing frequencies increased in response to taste substances applied to TBC receptor membranes. Under the whole-cell clamp mode, as expected, TBCs produced various voltage-gated currents such as TTX-sensitive Na+ currents (INa), outward currents (Iout) including TEA-sensitive and insensitive currents, inward rectifier K+ currents (Iir), and Ca2+ currents including T-type, P/Q-type, and L-type Ca2+ currents. We classified TBCs into three types based on the magnitude of their voltage-gated Na+ currents and membrane capacitance. HEX type (60% of TBCs examined) was significantly larger in Na+ current magnitude and smaller in membrane capacitance than LEX type (23%). NEX type (17%) had no Na+ currents. HEX type was equally distributed within single taste buds, while LEX type was centrally distributed, and NEX type was peripherally distributed. There were correlations between these electrophysiological cell types and morphological cell types determined by three-dimensional reconstruction. The present results show that soft palate taste buds contain TBCs with different electrophysiological properties, and suggest that their co-operation is required in taste transduction.
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Affiliation(s)
- Tomohiro Noguchi
- Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Kitakyushu, Fukuoka 808-0196, Japan
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24
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Abstract
Gustatory perception arises not only from intracellular transduction cascades within taste receptor cells but also from cell-to-cell communication among the cells of the taste bud. This study presents novel data demonstrating that the brain-gut peptide cholecystokinin (CCK) is expressed in subsets of taste receptor cells, and that it may play a signaling role unknown previously within the taste bud. Immunocytochemistry revealed positively stained subsets of cells within taste buds throughout the oral cavity. These cells typically displayed round nuclei with full processes, similar to those classified as light cells. Peptide expression was verified using nested PCR on template cDNA derived from mRNA extracted from isolated posterior taste buds. Multiple physiological actions of cholecystokinin on taste receptor cells were observed. An outward potassium current, recorded with the patch-clamp technique, was inhibited by exogenous application of sulfated cholecystokinin octapeptide in a reversible and concentration-dependent manner. Pharmacological analysis suggests that this inhibition is mediated by CCK-A receptors and involves PKC phosphorylation. An inwardly rectifying potassium current, typically invariant to stimulation, was also inhibited by cholecystokinin. Additionally, exogenous cholecystokinin was effective in elevating intracellular calcium as measured by ratiometric techniques with the calcium-sensitive dye fura-2. Pharmacology similarly demonstrated that these calcium elevations were mediated by CCK-A receptors and were dependent on intracellular calcium stores. Collectively, these observations suggest a newly discovered role for peptide neuromodulation in the peripheral processing of taste information.
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25
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Herness S, Zhao FL, Kaya N, Lu SG, Shen T, Sun XD. Adrenergic signalling between rat taste receptor cells. J Physiol 2002; 543:601-14. [PMID: 12205193 PMCID: PMC2290507 DOI: 10.1113/jphysiol.2002.020438] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
In taste buds, synaptic transmission is traditionally thought to occur from taste receptor cells to the afferent nerve. This communication reports the novel observation that taste receptor cells respond to adrenergic stimulation. Noradrenaline application inhibited outward potassium currents in a dose-dependent manner. This inhibition was mimicked by the beta agonist isoproterenol and blocked by the beta antagonist propranolol. The alpha agonists clonidine and phenylephrine both inhibited the potassium currents and elevated intracellular calcium levels. Inwardly rectifying potassium currents were unaffected by adrenergic stimulation. Experiments using the RT-PCR technique demonstrate that lingual epithelium expresses multiple alpha (alpha1a, alpha1b, alpha1c, alpha1d, alpha2a, alpha2b, alpha2c) and beta (beta1, beta2) subtypes of adrenergic receptors, and immunocytochemistry localized noradrenaline to a subset of taste receptor cells. Collectively, these data imply strongly that adrenergic transmission within the taste bud may play a paracrine role in taste physiology.
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MESH Headings
- Adrenergic alpha-Agonists/analysis
- Adrenergic alpha-Agonists/pharmacology
- Adrenergic beta-Agonists/pharmacology
- Animals
- Epithelial Cells/physiology
- Gene Expression
- Immunohistochemistry
- Isoproterenol/pharmacology
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Neurons, Afferent/chemistry
- Neurons, Afferent/physiology
- Norepinephrine/analysis
- Norepinephrine/pharmacology
- Paracrine Communication/drug effects
- Paracrine Communication/physiology
- Potassium/metabolism
- Potassium Channels, Inwardly Rectifying/physiology
- RNA, Messenger/analysis
- Rats
- Rats, Sprague-Dawley
- Receptors, Adrenergic, alpha/genetics
- Receptors, Adrenergic, alpha/metabolism
- Receptors, Adrenergic, beta/genetics
- Receptors, Adrenergic, beta/metabolism
- Synaptic Transmission/drug effects
- Synaptic Transmission/physiology
- Taste/physiology
- Taste Buds/chemistry
- Taste Buds/physiology
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Affiliation(s)
- Scott Herness
- Department of Oral Biology, College of Dentistry, Ohio State University, 305 West 12th Avenue, Columbus, OH 43210, USA.
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26
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Zhao FL, Lu SG, Herness S. Dual actions of caffeine on voltage-dependent currents and intracellular calcium in taste receptor cells. Am J Physiol Regul Integr Comp Physiol 2002; 283:R115-29. [PMID: 12069937 DOI: 10.1152/ajpregu.00410.2001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Although the numerous stimuli representing the taste quality of bitterness are known to be transduced through multiple mechanisms, recent studies have suggested an unpredicted complexity of the transduction pathways for individual bitter stimuli. To investigate this notion more thoroughly, a single prototypic bitter stimulus, caffeine, was studied by using patch-clamp and ratiometric imaging techniques on dissociated rat taste receptor cells. At behaviorally relevant concentrations, caffeine produced strong inhibition of outwardly and inwardly rectifying potassium currents. Caffeine additionally inhibited calcium current, produced a weaker inhibition of sodium current, and was without effect on chloride current. Consistent with its effects on voltage-dependent currents, caffeine caused a broadening of the action potential and an increase of the input resistance. Caffeine was an effective stimulus for elevation of intracellular calcium. This elevation was concentration dependent, independent of extracellular calcium or ryanodine, and dependent on intracellular stores as evidenced by thapsigargin treatment. These dual actions on voltage-activated ionic currents and intracellular calcium levels suggest that a single taste stimulus, caffeine, utilizes multiple transduction mechanisms.
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Affiliation(s)
- Fang-Li Zhao
- Department of Oral Biology, College of Dentistry, Ohio State University, 305 West 12th Avenue, Columbus, OH 43210, USA
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27
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Ogura T. Acetylcholine increases intracellular Ca2+ in taste cells via activation of muscarinic receptors. J Neurophysiol 2002; 87:2643-9. [PMID: 12037167 DOI: 10.1152/jn.2002.87.6.2643] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Previous studies suggest that acetylcholine (ACh) is a transmitter released from taste cells as well as a transmitter in cholinergic efferent neurons innervating taste buds. However, the physiological effects on taste cells have not been established. I examined effects of ACh on taste-receptor cells by monitoring [Ca2+]i. ACh increased [Ca2+]i in both rat and mudpuppy taste cells. Atropine blocked the ACh response, but D-tubocurarine did not. U73122, a phospholipase C inhibitor, and thapsigargin, a Ca2+-ATPase inhibitor that depletes intracellular Ca2+ stores, blocked the ACh response. These results suggest that ACh binds to M1/M3/M5-like subtypes of muscarinic ACh receptors, causing an increase in inositol 1,4,5-trisphosphate and subsequent release of Ca2+ from the intracellular stores. A long incubation with ACh induced a transient response followed by a sustained phase of [Ca2+]i increase. In Ca2+-free solution, the sustained phases disappeared, suggesting that Ca2+ influx is involved in the sustained phase. Depletion of Ca2+ stores by thapsigargin alone induced Ca2+ influx. These findings suggest that Ca2+ store-operated channels may be present in taste cells and that they may participate in the sustained phase of [Ca2+]i increase. Immunocytochemical experiments indicated that the M1 subtype of muscarinic receptors is present in both rat and mudpuppy taste cells.
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Affiliation(s)
- Tatsuya Ogura
- Department of Anatomy and Neurobiology, Colorado State University, Fort Collins 80523, USA.
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28
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Vanoye CG, George AL. Functional characterization of recombinant human ClC-4 chloride channels in cultured mammalian cells. J Physiol 2002; 539:373-83. [PMID: 11882671 PMCID: PMC2290165 DOI: 10.1113/jphysiol.2001.013115] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Members of the ClC chloride channel family participate in several physiological processes and are linked to human genetic diseases. The physiological role of ClC-4 is unknown and previous detailed characterizations of recombinant human ClC-4 (hClC-4) have provided conflicting results. To re-examine the hClC-4 phenotype, recombinant hClC-4 was expressed in three distinct mammalian cell lines and characterized using patch-clamp techniques. In all cells, the expression of hClC-4 generated strongly outward-rectifying Cl(-) currents with the conductance sequence: SCN(-) >> NO(3)(-) >> Cl(-) > Br(-) approximate I(-) >> aspartate. Continuous activity of hClC-4 was sustained to different degrees by internal nucleotides: ATP approximately ATPgammaS >> AMP-PNP approximate GTP > ADP. Although non-hydrolysable nucleotides are sufficient for channel function, ATP hydrolysis is required for full activity. Changing the extracellular (2 mM or nominal Ca(2+)-free) or intracellular Ca(2+) (25 or 250 nM) concentration did not alter hClC-4 currents. Acidification of external pH (pH(o)) inhibited hClC-4 currents (half-maximal inhibition approximate 6.19), whereas neither external alkalinization to pH 8.4 nor internal acidification to pH 6.0 reduced current levels. Single-channel recordings demonstrated a Cl(-) channel active only at depolarizing potentials with a slope conductance of approximately 3 pS. Acidic pH(o) did not alter single-channel conductance. We conclude that recombinant hClC-4 encodes a small-conductance, nucleotide-dependent, Ca(2+)-independent outward-rectifying chloride channel that is inhibited by external acidification. This detailed characterization will be highly valuable in comparisons of hClC-4 function with native chloride channel activities and for future structure-function correlations.
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Affiliation(s)
- Carlos G Vanoye
- Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232, USA
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29
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Abstract
Taste buds are sensory end organs that detect chemical substances occurring in foodstuffs and relay the relative information to the brain. The mechanisms by which the chemical stimuli are converted into biological signals represent a central issue in taste research. Our understanding of how taste buds accomplish this operation relies on the detailed knowledge of the biological properties of taste bud cells-the taste cells-and of the functional processes occurring in these cells during chemostimulation. The amphibian Necturus maculosus (mudpuppy) has proven to be a very useful model for studying basic cellular processes of vertebrate taste reception, some of which are still awaiting to be explored in mammals. The main advantages offered by Necturus are the large size of its taste cells and the relative accessibility of its taste buds, which can therefore be handled easily for experimental manipulations. In this review, I summarize the functional properties of Necturus taste cells studied with electrophysiological techniques (intracellular recordings and patch-clamp recordings). My focus is on ion channels in taste cells and on their role in signal transduction, as well as on the functional relationships among the cells inside Necturus taste buds. This information has revealed to be well suited to outline some of the general physiological processes occurring during taste reception in vertebrates, including mammals, and may represent a useful framework for understanding how taste buds work.
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Affiliation(s)
- Albertino Bigiani
- Dipartimento di Scienze Biomediche, Sezione di Fisiologia, Università di Modena e Reggio Emilia, via Campi 287, Italy.
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30
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Abstract
The mammalian peripheral taste system undergoes functional changes during postnatal development. These changes could reflect age-dependent alterations in the membrane properties of taste cells, which use a vast array of ion channels for transduction mechanisms. Yet, scarce information is available on the membrane events in developing taste cells. We have addressed this issue by studying voltage-dependent Na+, K+, and Cl- currents (I(Na), I(K), and I(Cl), respectively) in a subset of taste cells (the so-called "Na/OUT" cells, which are electrically excitable and thought to be sensory) from mouse vallate papilla. Voltage-dependent currents play a key role during taste transduction, especially in the generation of action potentials. Patch-clamp recordings revealed that I(Na), I(K), and I(Cl) were expressed early in postnatal development. However, only I(K) and I(Cl) densities increased significantly in developing Na/OUT cells. Consistent with the rise of I(K) density, we found that action potential waveform changed markedly, with an increased speed of repolarization that was accompanied by an enhanced capability of repetitive firing. In addition to membrane excitability changes in putative sensory cells, we observed a concomitant increase in the occurrence of glia-like taste cells (the so called "leaky" cells) among patched cells. Leaky cells are likely involved in dissipating the increase of extracellular K+ during action potential discharge in chemosensory cells. Thus, developing taste cells of the mouse vallate papilla undergo a significant electrophysiological maturation and diversification. These functional changes may have a profound impact on the transduction capabilities of taste buds during development.
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31
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Abstract
Taste is the sensory system devoted primarily to a quality check of food to be ingested. Although aided by smell and visual inspection, the final recognition and selection relies on chemoreceptive events in the mouth. Emotional states of acute pleasure or displeasure guide the selection and contribute much to our quality of life. Membrane proteins that serve as receptors for the transduction of taste have for a long time remained elusive. But screening the mass of genome sequence data that have recently become available has provided a new means to identify key receptors for bitter and sweet taste. Molecular biology has also identified receptors for salty, sour and umami taste.
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Affiliation(s)
- B Lindemann
- Department of Physiology, Universität des Saarlandes, Homburg, Germany.
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32
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Abstract
Taste buds are sensory structures made up by tightly packed, specialized epithelial cells called taste cells. Taste cells are functionally heterogeneous, and a large proportion of them fire action potentials during chemotransduction. In view of the narrow intercellular spaces within the taste bud, it is expected that the ionic composition of the extracellular fluid surrounding taste cells may be altered significantly by activity. This consideration has led to postulate the existence of glialike cells that could control the microenvironment in taste buds. However, the functional identification of such cells has been so far elusive. By using the patch-clamp technique in voltage-clamp conditions, I identified a new type of cells in the taste buds of the mouse vallate papilla. These cells represented about 30% of cells patched in taste buds and were characterized by a large leakage current. Accordingly, I named them "Leaky" cells. The leakage current was carried by K(+), and was blocked by Ba(2+) but not by tetraethylammonium (TEA). Other taste cells, such as those possessing voltage-gated Na(+) currents and thought to be chemosensory in function, did not express any sizeable leakage current. Consistent with the presence of a leakage conductance, Leaky cells had a low input resistance (approximately 0.25 G Omega). In addition, their zero-current ("resting") potential was close to the equilibrium potential for potassium ions. The electrophysiological analysis of the membrane currents remaining after pharmacological block by Ba(2+) revealed that Leaky cells also possessed a Cl(-) conductance. However, in resting conditions the membrane of these cells was about 60 times more permeable to K(+) than to Cl(-). The resting potassium conductance in Leaky cells could be involved in dissipating rapidly the increase in extracellular K(+) during action potential discharge in chemosensory cells. Thus Leaky cells might represent glialike elements in taste buds. These findings support a model in which specific cells control the chemical composition of intercellular fluid in taste buds.
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Affiliation(s)
- A Bigiani
- Dipartimento di Scienze Biomediche, Sezione di Fisiologia, Università di Modena e Reggio Emilia, 41100 Modena, Italy.
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33
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Abstract
Acid and salt responses of taste cells induced by natural stimulation have not been investigated with exception of early studies with conventional microelectrode method, due to the toxicity of high concentration of salt or low pH of acid stimuli applied to isolated taste cells. This indicates that the application of rapid and localized stimulation to the apical membrane of taste cells is necessary for recording of natural responses to salt or acid stimuli using patch clamp technique. Recently we have developed a procedure to accomplish the quasi-natural condition including rapid, localized stimuli to the apical receptive membrane and the maintenance of taste bud polarity. In this review, we present our recent results obtained under quasi-natural condition using patch clamp techniques, comparing with the previously proposed hypothesis. One of our major finding is the fact that the acid-induced responses of taste cells in the mouse fungiform papillae are never suppressed by amiloride but an apical proton-gated conductance and a basolateral Cl(-) conductance possibly contribute to sour transduction. On the other hand, salt-induced responses are suppressed by amiloride, although the salt-induced responses recorded from a single cell involve both amiloride-sensitive and -insensitive components. Furthermore, the amiloride-insensitive component of salt responses possibly consists of multiple subcomponents including an apical sodium-gated nonselective cation conductance and a basolateral Cl(-) conductance. Recent reports also support the hypothesis that both acid and salt responses require specific receptor mechanisms of inorganic cations such as H(+) and Na(+) at the apical receptive membrane.
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Affiliation(s)
- T Miyamoto
- Department of Physiology, Nagasaki University School of Dentistry, 1-7-1 Sakamoto, 852-8588, Nagasaki, Japan.
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34
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Kim YV, Bobkov YV, Kolesnikov SS. Adenosine triphosphate mobilizes cytosolic calcium and modulates ionic currents in mouse taste receptor cells. Neurosci Lett 2000; 290:165-8. [PMID: 10963889 DOI: 10.1016/s0304-3940(00)01342-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
By using photometry and the patch clamp technique, we identified P(2Y)-like receptors in mouse taste receptor cells (TRCs) and found them to be coupled to Ca(2+) mobilization and ionic current modulation. Particularly, adenosine triphosphate (ATP) and the P(2Y) agonist 2-methylthio-ATP increased intracellular Ca(2+) by stimulating the phosphoinositide pathway, whereas beta, gamma-methylene-D-ATP, a P(2X) agonist, was ineffective. In a distinctive TRC subpopulation, ATP closed Ca(2+) channels. This regulation may underlie the negative feedback tuning neurotransmitter release. By mobilizing intracellular Ca(2+), ATP activated Ca(2+)-dependent Cl(-) channels, the intracellular event that may universally occur upon taste stimulation triggering IP(3) formation and Ca(2+) release in the TRC cytoplasm.
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Affiliation(s)
- Y V Kim
- Institute of Cell Biophysics, Russian Academy of Sciences, Moscow Region, 142290, Pushchino, Russia
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