751
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Rozengurt E, Sternini C. Taste receptor signaling in the mammalian gut. Curr Opin Pharmacol 2007; 7:557-62. [PMID: 18024184 DOI: 10.1016/j.coph.2007.10.002] [Citation(s) in RCA: 146] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2007] [Revised: 10/01/2007] [Accepted: 10/05/2007] [Indexed: 12/12/2022]
Abstract
Molecular sensing by gastrointestinal (GI) cells plays a crucial role in the control of multiple fundamental functions including digestion, regulation of caloric intake, pancreatic insulin secretion, and metabolism, as well as protection from ingested harmful drugs and toxins. These processes are likely to be mediated by the initiation of humoral and/or neural pathways through the activation of endocrine cells. However, the initial recognition events and mechanism(s) involved are still largely unknown. This article reviews the current evidence that the chemosensory machinery discovered in specialized neuroepithelial taste receptor cells of the lingual epithelium is operational in enteroendocrine open GI cells that sense the chemical composition of the luminal contents of the gut.
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Affiliation(s)
- Enrique Rozengurt
- Division of Digestive Diseases and CURE, Digestive Diseases Research Center, David Geffen School of Medicine, University of California at Los Angeles, 900 Veteran Avenue, Los Angeles, CA 90095, USA.
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752
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Behavioral discrimination between sucrose and other natural sweeteners in mice: implications for the neural coding of T1R ligands. J Neurosci 2007; 27:11242-53. [PMID: 17942718 DOI: 10.1523/jneurosci.1227-07.2007] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
In taste bud cells, two different T1R heteromeric taste receptors mediate signal transduction of sugars (the canonical "sweet" taste receptor, T1R2 + T1R3) and L-amino acids (the T1R1 + T1R3 receptor). The T1R1 + T1R3 receptor is thought to mediate what is considered the fifth basic taste quality "umami." However, a subset of L-amino acids is "sweet tasting" to humans and appears to possess a "sucrose-like" taste quality to nonhuman mammals. This suggests, to varying degrees, that all of these compounds activate a single neural channel that leads to the perception of sweetness. The experiments detailed here were designed to test the ability of mice to distinguish between sucrose and various others sugars and L-amino acids in operant taste discrimination tasks. Mice had at least some difficulty discriminating sucrose from L-serine, L-threonine, maltose, fructose, and glucose. For example, when concentration effects are taken into consideration, mice discriminated poorly, if at all, sucrose from glucose or fructose and, to a lesser extent maltose, suggesting that sugars generate a unitary perceptual quality. However, mice were able to reliably discriminate sucrose from L-serine and L-threonine. Data gathered using a conditioned taste aversion assay also suggest that, although qualitatively similar to the taste of sucrose, L-serine and L-threonine generate distinctive percepts. In conclusion, it appears that some signals from taste receptor proteins binding with sugars and some L-amino acids converge somewhere along the gustatory neuraxis. However, the results of these experiments also imply that sweet-tasting L-amino acids may possess qualitative taste characteristics that are distinguishable from the prototypical sweetener sucrose.
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753
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Dahanukar A, Lei YT, Kwon JY, Carlson JR. Two Gr genes underlie sugar reception in Drosophila. Neuron 2007; 56:503-16. [PMID: 17988633 PMCID: PMC2096712 DOI: 10.1016/j.neuron.2007.10.024] [Citation(s) in RCA: 306] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2007] [Revised: 09/18/2007] [Accepted: 10/18/2007] [Indexed: 10/22/2022]
Abstract
We have analyzed the molecular basis of sugar reception in Drosophila. We define the response spectrum, concentration dependence, and temporal dynamics of sugar-sensing neurons. Using in situ hybridization and reporter gene expression, we identify members of the Gr5a-related taste receptor subfamily that are coexpressed in sugar neurons. Neurons expressing reporters of different Gr5a-related genes send overlapping but distinct projections to the brain and thoracic ganglia. Genetic analysis of receptor genes shows that Gr5a is required for response to one subset of sugars and Gr64a for response to a complementary subset. A Gr5a;Gr64a double mutant shows no physiological or behavioral responses to any tested sugar. The simplest interpretation of our results is that Gr5a and Gr64a are each capable of functioning independently of each other within individual sugar neurons and that they are the primary receptors used in the labellum to detect sugars.
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Affiliation(s)
- Anupama Dahanukar
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103
| | - Ya-Ting Lei
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103
| | - Jae Young Kwon
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103
| | - John R. Carlson
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT 06520-8103
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754
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Toyono T, Seta Y, Kataoka S, Toyoshima K. CCAAT/Enhancer-binding protein β regulates expression of human T1R3 taste receptor gene in the bile duct carcinoma cell line, HuCCT1. ACTA ACUST UNITED AC 2007; 1769:641-8. [DOI: 10.1016/j.bbaexp.2007.08.003] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2007] [Revised: 08/02/2007] [Accepted: 08/17/2007] [Indexed: 11/26/2022]
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755
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Winnig M, Bufe B, Kratochwil NA, Slack JP, Meyerhof W. The binding site for neohesperidin dihydrochalcone at the human sweet taste receptor. BMC STRUCTURAL BIOLOGY 2007; 7:66. [PMID: 17935609 PMCID: PMC2099433 DOI: 10.1186/1472-6807-7-66] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/07/2007] [Accepted: 10/12/2007] [Indexed: 11/10/2022]
Abstract
Background Differences in sweet taste perception among species depend on structural variations of the sweet taste receptor. The commercially used isovanillyl sweetener neohesperidin dihydrochalcone activates the human but not the rat sweet receptor TAS1R2+TAS1R3. Analysis of interspecies combinations and chimeras of rat and human TAS1R2+TAS1R3 suggested that the heptahelical domain of human TAS1R3 is crucial for the activation of the sweet receptor by neohesperidin dihydrochalcone. Results By mutational analysis combined with functional studies and molecular modeling we identified a set of different amino acid residues within the heptahelical domain of human TAS1R3 that forms the neohesperidin dihydrochalcone binding pocket. Sixteen amino acid residues in the transmembrane domains 2 to 7 and one in the extracellular loop 2 of hTAS1R3 influenced the receptor's response to neohesperidin dihydrochalcone. Some of these seventeen residues are also part of the binding sites for the sweetener cyclamate or the sweet taste inhibitor lactisole. In line with this observation, lactisole inhibited activation of the sweet receptor by neohesperidin dihydrochalcone and cyclamate competitively, whereas receptor activation by aspartame, a sweetener known to bind to the N-terminal domain of TAS1R2, was allosterically inhibited. Seven of the amino acid positions crucial for activation of hTAS1R2+hTAS1R3 by neohesperidin dihydrochalcone are thought to play a role in the binding of allosteric modulators of other class C GPCRs, further supporting our model of the neohesperidin dihydrochalcone pharmacophore. Conclusion From our data we conclude that we identified the neohesperidin dihydrochalcone binding site at the human sweet taste receptor, which overlaps with those for the sweetener cyclamate and the sweet taste inhibitor lactisole. This readily delivers a molecular explanation of our finding that lactisole is a competitive inhibitor of the receptor activation by neohesperidin dihydrochalcone and cyclamate. Some of the amino acid positions crucial for activation of hTAS1R2+hTAS1R3 by neohesperidin dihydrochalcone are involved in the binding of allosteric modulators in other class C GPCRs, suggesting a general role of these amino acid positions in allosterism and pointing to a common architecture of the heptahelical domains of class C GPCRs.
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Affiliation(s)
- Marcel Winnig
- German Institute of Human Nutrition Potsdam-Rehbruecke, Department of Molecular Genetics, Arthur-Scheunert Allee 114-116, 14558 Nuthetal, Germany.
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756
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Hisatsune C, Yasumatsu K, Takahashi-Iwanaga H, Ogawa N, Kuroda Y, Yoshida R, Ninomiya Y, Mikoshiba K. Abnormal taste perception in mice lacking the type 3 inositol 1,4,5-trisphosphate receptor. J Biol Chem 2007; 282:37225-31. [PMID: 17925404 DOI: 10.1074/jbc.m705641200] [Citation(s) in RCA: 121] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Inositol 1,4,5-trisphosphate receptor (IP3R) is one of the important calcium channels expressed in the endoplasmic reticulum and has been shown to play crucial roles in various physiological phenomena. Type 3 IP3R is expressed in taste cells, but the physiological relevance of this receptor in taste perception in vivo is still unknown. Here, we show that mice lacking IP3R3 show abnormal behavioral and electrophysiological responses to sweet, umami, and bitter substances that trigger G-protein-coupled receptor activation. In contrast, responses to salty and acid tastes are largely normal in the mutant mice. We conclude that IP3R3 is a principal mediator of sweet, bitter, and umami taste perception and would be a missing molecule linking phospholipase C beta2 to TRPM5 activation.
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Affiliation(s)
- Chihiro Hisatsune
- Laboratory for Developmental Neurobiology, RIKEN Brain Science Institute, 2-1 Hirosawa, Wako city, Saitama 351-0198, Japan.
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757
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Inoue M, Glendinning JI, Theodorides ML, Harkness S, Li X, Bosak N, Beauchamp GK, Bachmanov AA. Allelic variation of the Tas1r3 taste receptor gene selectively affects taste responses to sweeteners: evidence from 129.B6-Tas1r3 congenic mice. Physiol Genomics 2007; 32:82-94. [PMID: 17911381 PMCID: PMC2259227 DOI: 10.1152/physiolgenomics.00161.2007] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The Tas1r3 gene encodes the T1R3 receptor protein, which is involved in sweet taste transduction. To characterize ligand specificity of the T1R3 receptor and the genetic architecture of sweet taste responsiveness, we analyzed taste responses of 129.B6-Tas1r3 congenic mice to a variety of chemically diverse sweeteners and glucose polymers with three different measures: consumption in 48-h two-bottle preference tests, initial licking responses, and responses of the chorda tympani nerve. The results were generally consistent across the three measures. Allelic variation of the Tas1r3 gene influenced taste responsiveness to nonnutritive sweeteners (saccharin, acesulfame-K, sucralose, SC-45647), sugars (sucrose, maltose, glucose, fructose), sugar alcohols (erythritol, sorbitol), and some amino acids (D-tryptophan, D-phenylalanine, L-proline). Tas1r3 genotype did not affect taste responses to several sweet-tasting amino acids (L-glutamine, L-threonine, L-alanine, glycine), glucose polymers (Polycose, maltooligosaccharide), and nonsweet NaCl, HCl, quinine, monosodium glutamate, and inosine 5'-monophosphate. Thus Tas1r3 polymorphisms affect taste responses to many nutritive and nonnutritive sweeteners (all of which must interact with a taste receptor involving T1R3), but not to all carbohydrates and amino acids. In addition, we found that the genetic architecture of sweet taste responsiveness changes depending on the measure of taste response and the intensity of the sweet taste stimulus. Variation in the T1R3 receptor influenced peripheral taste responsiveness over a wide range of sweetener concentrations, but behavioral responses to higher concentrations of some sweeteners increasingly depended on mechanisms that could override input from the peripheral taste system.
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Affiliation(s)
- Masashi Inoue
- Laboratory of Cellular Neurobiology, School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo, Japan
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758
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Levoye A, Jockers R. [GPCRs heterodimerization: a new way towards the discovery of function for the orphan receptors?]. Med Sci (Paris) 2007; 23:746-50. [PMID: 17875294 DOI: 10.1051/medsci/20072389746] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
G protein-coupled receptors (GPCRs), also called seven transmembrane domain (7TM) proteins, represent the largest family of cell surface receptors. GPCRs control a variety of physiological processes, are involved in multiple diseases and are major drug targets. Despite a vast effort of academic and industrial research, more than one hundred receptors remain orphans. These orphan GPCRs offer a great potential for drug discovery, as almost 60% of currently prescribed drugs target GPCRs. Deorphenization strategies have concentrated mainly on the identification of the natural ligands of these proteins. Recent advances have shown that orphan GPCRs, similar to orphan nuclear receptors, can regulate the function of non-orphan receptors by heterodimerization. These findings not only help to better understand the extraordinary diversity of GPCRs, but also open new perspectives for the identification of the function of these orphan receptors that hold great therapeutic potential.
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Affiliation(s)
- Angélique Levoye
- Institut Pasteur, Laboratoire de Pathogénie Virale Moléculaire, INSERM U819, Département de Virologie, 28, rue du Docteur Roux, 75724, Paris, France.
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759
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Abstract
This review focuses on behavioral genetic studies of sweet, umami, bitter and salt taste responses in mammals. Studies involving mouse inbred strain comparisons and genetic analyses, and their impact on elucidation of taste receptors and transduction mechanisms are discussed. Finally, the effect of genetic variation in taste responsiveness on complex traits such as drug intake is considered. Recent advances in development of genomic resources make behavioral genetics a powerful approach for understanding mechanisms of taste.
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Affiliation(s)
- John D Boughter
- Department of Anatomy & Neurobiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA
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760
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Abstract
Although there have been many recent advances in the field of gustatory neurobiology, our knowledge of how the nervous system is organized to process information about taste is still far from complete. Many studies on this topic have focused on understanding how gustatory neural circuits are spatially organized to represent information about taste quality (e.g., "sweet", "salty", "bitter", etc.). Arguments pertaining to this issue have largely centered on whether taste is carried by dedicated neural channels or a pattern of activity across a neural population. But there is now mounting evidence that the timing of neural events may also importantly contribute to the representation of taste. In this review, we attempt to summarize recent findings in the field that pertain to these issues. Both space and time are variables likely related to the mechanism of the gustatory neural code: information about taste appears to reside in spatial and temporal patterns of activation in gustatory neurons. What is more, the organization of the taste network in the brain would suggest that the parameters of space and time extend to the neural processing of gustatory information on a much grander scale.
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Affiliation(s)
- Christian H Lemon
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, 855 Monroe Ave., Suite 515, Memphis, TN 38163, USA
| | - Donald B Katz
- Department of Psychology and Volen National Center for Complex Systems, Brandeis University, Volen 208/MS 013, 415 South St., Waltham, MA 02454, USA
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761
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Hass N, Schwarzenbacher K, Breer H. A cluster of gustducin-expressing cells in the mouse stomach associated with two distinct populations of enteroendocrine cells. Histochem Cell Biol 2007; 128:457-71. [PMID: 17874119 DOI: 10.1007/s00418-007-0325-3] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/31/2007] [Indexed: 12/22/2022]
Abstract
In the gastrointestinal (GI) tract, a variety of digestive processes are continually adapted to the changing composition of ingested foods, which requires a precise chemosensory monitoring of luminal contents. Gustducin-expressing brush cells scattered throughout the GI mucosa are considered candidate sensory cells for accomplishing this task. In this study, we have investigated a large cluster of gustducin-positive cells which is located exactly at the boundary between the fundic and the oxyntic mucosa of the mouse stomach, at the so-called "limiting ridge". In close association with the candidate chemosensory cluster, we found two populations of enteroendocrine cells: one population containing the satiety regulating hormone ghrelin, the other population comprising serotonin-secreting enterochromaffin cells. The particular arrangement of gustducin-expressing cells and enteroendocrine cells at the limiting ridge suggests a direct interplay between these cell types with immediate implications, not only for digestive processes in the stomach, but also for parameters controlling the satiety status.
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Affiliation(s)
- Nicole Hass
- University of Hohenheim, Institute of Physiology, Garbenstrasse 30, 70599, Stuttgart, Germany
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762
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Durzyński L, Gaudin JC, Breuils L, Szydłowski J, Goździcka-Józefiak A, Haertlé T. Do G protein-coupled receptors expressed in human lingual epithelium interact with HPV11? J Med Virol 2007; 79:1545-54. [PMID: 17705193 DOI: 10.1002/jmv.20996] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Human papillomaviruses infect epithelia but little is known about the nature of cell surface receptors interacting with the viral particles. It has been proposed that glycosaminoglycans and integrins may be involved in the attachment process. In the present study, the putative interactions of virus-like particles of human papillomavirus type 11 (HPV11), which present a tropism for nasopharyngeal epithelia, with olfactory and taste receptors expressed in the human lingual epithelium were studied. The L1 protein of HPV11 was produced in insect cells. The presence of L1 virus-like particles was analyzed by ELISA using monoclonal antibodies specific for full-size particles and by electron microscopy. Using immunofluorescence, it was observed that virus-like particles interacted with taste buds from murine tongue, with the tagged human olfactory receptor hJCG5 expressed in HEK-293 but not with the tagged taste receptor hT2R4. This therefore suggests that hJCG5 may be involved in the adsorption process of HPV11 to lingual epithelium serving as a so-called "adsorption-adhesive molecule."
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Affiliation(s)
- Lukasz Durzyński
- A. Mickiewicz University, Institute of Experimental Biology, Poznań, Poland
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763
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Ogura T, Margolskee RF, Tallini YN, Shui B, Kotlikoff MI, Lin W. Immuno-localization of vesicular acetylcholine transporter in mouse taste cells and adjacent nerve fibers: indication of acetylcholine release. Cell Tissue Res 2007; 330:17-28. [PMID: 17704949 DOI: 10.1007/s00441-007-0470-y] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Accepted: 07/11/2007] [Indexed: 10/22/2022]
Abstract
Acetylcholine (ACh) is well established as a neurotransmitter and/or neuromodulator in various organs. Previously, it has been shown by Ogura (J Neurophysiol 87:2643-2649, 2002) that in both physiological and immunohistochemical studies the muscarinic acetylcholine (ACh) receptor is present in taste receptor cells. However, it has not been determined if ACh is released locally from taste receptor cells and/or surrounding nerve fibers. In this study we investigated the sites of ACh release in mouse taste tissue using the antisera against vesicular ACh transporter (VAChT), a key element of ACh-containing vesicles. Our data show that VAChT-immunoreactivity is present in many taste receptor cells, including cells expressing the transient receptor potential channel M5 (TRPM5). In taste cells, VAChT-immunoreactivity was colocalized with the immunoreactivity to choline-acetyltransferase (ChAT), which synthesizes ACh. Additionally, enhanced green fluorescent protein (eGFP) was detected in the taste cells of BAC-transgenic mice, in which eGFP was placed under the control of endogenous ChAT transcriptional regulatory elements (ChAT(BAC)-eGFP mice). Furthermore, many ChAT-immunolabeled taste cells also reacted to an antibody against the vesicle-associated membrane protein synaptobrevin-2. These data suggest that ACh-containing vesicles are present in taste receptor cells and ACh release from taste cells may play a role in autocrine and/or paracrine cell-to-cell communication. In addition, certain nerve fibers surrounding or within taste buds were immunoreactive for the VAChT antibody. Some of these fibers were also immunolabeled with antibody against calcitonin gene-related peptide (CGRP), a marker for trigeminal peptidergic fibers. Thus, functions of taste receptor cells could be modulated by trigeminal fibers via ACh release as well.
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Affiliation(s)
- Tatsuya Ogura
- Department of Biological Sciences, University of Maryland Baltimore County, Baltimore, MD 21250, USA.
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764
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Breza JM, Curtis KS, Contreras RJ. Monosodium glutamate but not linoleic acid differentially activates gustatory neurons in the rat geniculate ganglion. Chem Senses 2007; 32:833-46. [PMID: 17693416 DOI: 10.1093/chemse/bjm052] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
To date, only one study has examined responses to monosodium glutamate (MSG) from gustatory neurons in the rat geniculate ganglion and none to free fatty acids. Accordingly, we recorded single-cell responses from geniculate ganglion gustatory neurons in anesthetized male rats to MSG and linoleic acid (LA), as well as to sucrose, NaCl, citric acid, and quinine hydrochloride. None of the 52 neurons responded to any LA concentration. In contrast, both narrowly tuned groups of gustatory neurons (sucrose specialists and NaCl specialists) responded to MSG, as did 2 of the broadly tuned groups (NaCl generalist(I) and acid generalists). NaCl-generalist(II) neurons responded only to the highest MSG concentration and only at low rates. No neuron type responded best to MSG; rather, responses to 0.1 M MSG were significantly less than those to NaCl for Na(+) -sensitive neurons and to sucrose for sucrose specialists. Interestingly, most Na(+) -sensitive neurons responded to 0.3 M MSG at levels comparable with those to 0.1 M NaCl, whereas sucrose specialists responded to 0.1 M MSG despite being unresponsive to NaCl. These results suggest that the stimulatory effect of MSG involves activation of sweet- or salt-sensitive receptors. We propose that glutamate underlies the MSG response of sucrose specialists, whereas Na(+) -sensitive neurons respond to the sodium cation. For the latter neuron groups, the large glutamate anion may reduce the driving force for sodium through epithelial channels on taste cell membranes. The observed concentration-dependent responses are consistent with this idea, as are cross-adaptation studies using 0.1 M concentrations of MSG and NaCl in subsets of these Na(+) -sensitive neurons.
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Affiliation(s)
- Joseph M Breza
- Department of Psychology, Program in Neuroscience, Florida State University, Tallahassee, FL 32306-1270, USA
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765
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Delay ER, Mitzelfelt JD, Westburg AM, Gross N, Duran BL, Eschle BK. Comparison of l-monosodium glutamate and l-amino acid taste in rats. Neuroscience 2007; 148:266-78. [PMID: 17629624 DOI: 10.1016/j.neuroscience.2007.05.045] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2007] [Revised: 05/18/2007] [Accepted: 05/24/2007] [Indexed: 11/24/2022]
Abstract
T1R2/T1R3 heterodimers are selectively responsive to sweet substances whereas T1R1/T1R3 receptors are selective for umami substances, represented by monosodium glutamate (MSG), and for L-amino acids. If a single receptor is responsible for detection of umami and L-amino acids, then it would be predicted that MSG and L-amino acids elicit similar tastes in rats. The present study compared the taste profile of MSG with four amino acids (glycine, L-proline, L-serine and L-arginine) using conditioned taste aversion, detection threshold, and taste discrimination methods. These experiments were designed to either reduce or neutralize the taste of sodium associated with MSG and the other amino acids. Detection threshold studies showed that rats were most sensitive to L-arginine and least sensitive to L-proline. Glycine and L-serine thresholds were similar to those previously reported for MSG. Like MSG, a conditioned taste aversion to each of the four amino acids generalized to sucrose in the presence of amiloride, a sodium channel blocker. Rats showed moderate generalization of aversion between MSG and L-arginine, suggesting that these two amino acids taste only moderately alike. However, the taste aversion experiments indicated that glycine, L-serine, and L-proline elicit taste sensations similar to MSG when amiloride is present. Discrimination experiments further compared the tastes of these three amino acids with MSG. When the sodium taste associated with MSG was reduced or neutralized, glycine and L-proline elicited tastes very similar but not identical to the taste of MSG. Low (but not higher) concentrations of L-serine were also difficult for rats to discriminate from MSG. While there are taste qualities common to all of these amino acids, the perceptual differences found in this study, combined with previous reports, suggest either multiple taste receptors and/or multiple signaling pathways may be involved in umami and amino acid taste perception in rats.
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Affiliation(s)
- E R Delay
- Department of Biology, Marsh Life Science, University of Vermont, Burlington, VT 05405, USA.
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766
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Roper SD. Signal transduction and information processing in mammalian taste buds. Pflugers Arch 2007; 454:759-76. [PMID: 17468883 PMCID: PMC3723147 DOI: 10.1007/s00424-007-0247-x] [Citation(s) in RCA: 191] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2006] [Accepted: 01/04/2007] [Indexed: 10/23/2022]
Abstract
The molecular machinery for chemosensory transduction in taste buds has received considerable attention within the last decade. Consequently, we now know a great deal about sweet, bitter, and umami taste mechanisms and are gaining ground rapidly on salty and sour transduction. Sweet, bitter, and umami tastes are transduced by G-protein-coupled receptors. Salty taste may be transduced by epithelial Na channels similar to those found in renal tissues. Sour transduction appears to be initiated by intracellular acidification acting on acid-sensitive membrane proteins. Once a taste signal is generated in a taste cell, the subsequent steps involve secretion of neurotransmitters, including ATP and serotonin. It is now recognized that the cells responding to sweet, bitter, and umami taste stimuli do not possess synapses and instead secrete the neurotransmitter ATP via a novel mechanism not involving conventional vesicular exocytosis. ATP is believed to excite primary sensory afferent fibers that convey gustatory signals to the brain. In contrast, taste cells that do have synapses release serotonin in response to gustatory stimulation. The postsynaptic targets of serotonin have not yet been identified. Finally, ATP secreted from receptor cells also acts on neighboring taste cells to stimulate their release of serotonin. This suggests that there is important information processing and signal coding taking place in the mammalian taste bud after gustatory stimulation.
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Affiliation(s)
- Stephen D Roper
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL 33136, USA.
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767
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Sainz E, Cavenagh MM, LopezJimenez ND, Gutierrez JC, Battey JF, Northup JK, Sullivan SL. The G-protein coupling properties of the human sweet and amino acid taste receptors. Dev Neurobiol 2007; 67:948-59. [PMID: 17506496 DOI: 10.1002/dneu.20403] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The human T1R taste receptors are family C G-protein-coupled receptors (GPCRs) that act as heterodimers to mediate sweet (hT1R2 + hT1R3) and umami (hT1R1 + hT1R3) taste modalities. Each T1R has a large extracellular ligand-binding domain linked to a seven transmembrane-spanning core domain (7TMD). We demonstrate that the 7TMDs of hT1R1 and hT1R2 display robust ligand-independent constitutive activity, efficiently catalyzing the exchange of GDP for GTP on Galpha subunits. In contrast, relative to the 7TMDs of hT1R1 and hT1R2, the 7TMD of hT1R3 couples poorly to G-proteins, suggesting that in vivo signaling may proceed primarily through hT1R1 and hT1R2. In addition, we provide direct evidence that the hT1Rs selectively signal through Galpha(i/o) pathways, coupling to multiple Galpha(i/o) subunits as well as the taste cell specific Gbeta(1)gamma(13) dimer.
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Affiliation(s)
- Eduardo Sainz
- Section on G-protein Coupled Receptors, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892, USA
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768
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Abstract
Electronic tongue systems are multisensor devices dedicated to automatic analysis of complicated composition samples and to the recognition of their characteristic properties. Recently, the number of publications covering this topic has significantly increased. Many possible architectures of such devices were proposed: potentiometric, voltammetric, as well as approaches embracing mass- and optical-sensors. For the analysis of sensor array data, various pattern recognition systems were proposed. All of these topics are summarized in this review. Moreover, additional problems are considered: miniaturization of electronic tongues and hybrid systems for liquid sensing.
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Affiliation(s)
- Patrycja Ciosek
- Department of Analytical Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664 Warsaw, Poland.
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769
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TRPM5, a taste-signaling transient receptor potential ion-channel, is a ubiquitous signaling component in chemosensory cells. BMC Neurosci 2007; 8:49. [PMID: 17610722 PMCID: PMC1931605 DOI: 10.1186/1471-2202-8-49] [Citation(s) in RCA: 186] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2007] [Accepted: 07/04/2007] [Indexed: 11/26/2022] Open
Abstract
Background A growing number of TRP channels have been identified as key players in the sensation of smell, temperature, mechanical forces and taste. TRPM5 is known to be abundantly expressed in taste receptor cells where it participates in sweet, amino acid and bitter perception. A role of TRPM5 in other sensory systems, however, has not been studied so far. Results Here, we systematically investigated the expression of TRPM5 in rat and mouse tissues. Apart from taste buds, where we found TRPM5 to be predominantly localized on the basolateral surface of taste receptor cells, TRPM5 immunoreactivity was seen in other chemosensory organs – the main olfactory epithelium and the vomeronasal organ. Most strikingly, we found solitary TRPM5-enriched epithelial cells in all parts of the respiratory and gastrointestinal tract. Based on their tissue distribution, the low cell density, morphological features and co-immunostaining with different epithelial markers, we identified these cells as brush cells (also known as tuft, fibrillovesicular, multivesicular or caveolated cells). In terms of morphological characteristics, brush cells resemble taste receptor cells, while their origin and biological role are still under intensive debate. Conclusion We consider TRPM5 to be an intrinsic signaling component of mammalian chemosensory organs, and provide evidence for brush cells being an important cellular correlate in the periphery.
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770
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771
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Springael JY, Urizar E, Costagliola S, Vassart G, Parmentier M. Allosteric properties of G protein-coupled receptor oligomers. Pharmacol Ther 2007; 115:410-8. [PMID: 17655934 DOI: 10.1016/j.pharmthera.2007.06.004] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2007] [Accepted: 06/07/2007] [Indexed: 11/18/2022]
Abstract
Allosteric regulation of ligand binding is a well-established mechanism regulating the function of G protein-coupled receptors (GPCR). Allosteric modulators have been considered so far as molecules binding to an allosteric site, distinct from that of the reference ligand (orthosteric site), and able to modulate the binding affinity at the orthosteric site and/or the signaling properties resulting from orthosteric site occupancy. Given that most GPCR are known to form dimers or higher order oligomers, we explored whether allosteric interactions could also occur between protomers within oligomeric arrays, thereby influencing binding and signaling receptor properties. Two main conclusions emerged from such studies. First, allosteric modulators can affect one receptor by binding to another receptor within a dimeric or oligomeric complex. Second, allosteric modulators might act on a given receptor by targeting the "orthosteric site" in another receptor of the complex. Allosteric regulation within di(oligo)mers thus implies that the pharmacological properties of a given receptor subtype can be influenced by the array of dimerization partners coexpressed in each particular cell type. Ligands could thus act as agonists or antagonists on 1 receptor, while modulating allosterically the function of a variety of other receptors to which they do not bind directly. Allosteric regulation across GPCR oligomeric interfaces is expected to greatly influence the practice of pharmacology. It will likely affect the design of drug discovery programs, which rely mostly on the overexpression of the receptor of interest in a cell line, thereby focusing on homo-oligomers and ignoring the potential effects of other partners.
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Affiliation(s)
- Jean-Yves Springael
- Institut de Recherche Interdisciplinaire en Biologie Humaine et Moléculaire (IRIBHM), Université Libre de Bruxelles, Campus Erasme, 808 Route de Lennik, Elsevier Inc, B-1070, Brussels, Belgium
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772
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Abstract
Tight junctions operate as semipermeable barriers in epithelial tissue, separating the apical from the basolateral sides of the cells. Membrane proteins of the claudin family represent the major tight junction constituents, and some reinforce permeability barriers, whereas others create pores based on solute size and ion selectivity. To outline paracellular permeability pathways in gustatory tissue, all claudins expressed in mouse taste buds and in human fungiform papillae have been characterized. Twelve claudins are expressed in murine taste-papillae-enriched tissue, and five of those are expressed in human fungiform papillae. A subset of the claudins expressed in mouse papillae is uniquely found in taste buds. By immunohistochemistry, claudin 4 has been found in mouse taste epithelium, with high abundance around the taste pore. Claudin 6 is explicitly detected inside the pore, claudin 7 was found at the basolateral side of taste cells, and claudin 8 was found around the pore. With the ion permeability features of the different claudins, a highly specific permeability pattern for paracellular diffusion is apparent, which indicates a peripheral mechanism for taste coding.
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Affiliation(s)
- Stéphanie Michlig
- Nestlé Research Center, Vers-chez-les-Blanc, Lausanne 1000, Switzerland
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773
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Oike H, Nagai T, Furuyama A, Okada S, Aihara Y, Ishimaru Y, Marui T, Matsumoto I, Misaka T, Abe K. Characterization of ligands for fish taste receptors. J Neurosci 2007; 27:5584-92. [PMID: 17522303 PMCID: PMC6672760 DOI: 10.1523/jneurosci.0651-07.2007] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Recent progress in the molecular biology of taste reception has revealed that in mammals, the heteromeric receptors T1R1/3 and T1R2/3 respond to amino acids and sweeteners, respectively, whereas T2Rs are receptors for bitter tastants. Similar taste receptors have also been characterized in fish, but their ligands have not been identified yet. In the present study, we conducted a series of experiments to identify the fish taste receptor ligands. Facial nerve recordings in zebrafish (Danio rerio) demonstrated that the fish perceived amino acids and even denatonium, which is a representative of aversive bitter compounds for mammals and Drosophila. Calcium imaging analysis of T1Rs in zebrafish and medaka fish (Oryzias latipes) using an HEK293T heterologous expression system revealed that both T1R1/3 and a series of T1R2/3 responded to amino acids but not to sugars. A triple-labeling, in situ hybridization analysis demonstrated that cells expressing T1R1/3 and T1R2/3s exist in PLCbeta2-expressing taste bud cells of medaka fish. Functional analysis using T2Rs showed that zfT2R5 and mfT2R1 responded to denatonium. Behavior observations confirmed that zebrafish prefer amino acids and avoid denatonium. These results suggest that, although there may be some fish-specific way of discriminating ligands, vertebrates could have a conserved gustatory mechanism by which T1Rs and T2Rs respond to attractive and aversive tastants, respectively.
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Affiliation(s)
- Hideaki Oike
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, and
| | - Toshitada Nagai
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, and
| | - Akira Furuyama
- Department of Oral Function and Molecular Biology, Ohu University School of Dentistry, Tomita-machi, Koriyama, Fukushima 963-8611, Japan
| | - Shinji Okada
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, and
| | - Yoshiko Aihara
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, and
| | - Yoshiro Ishimaru
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, and
| | - Takayuki Marui
- Department of Oral Function and Molecular Biology, Ohu University School of Dentistry, Tomita-machi, Koriyama, Fukushima 963-8611, Japan
| | - Ichiro Matsumoto
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, and
| | - Takumi Misaka
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, and
| | - Keiko Abe
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Bunkyo-ku, Tokyo 113-8657, Japan, and
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774
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Suga H, Haga T. Ligand screening system using fusion proteins of G protein-coupled receptors with G protein alpha subunits. Neurochem Int 2007; 51:140-64. [PMID: 17659814 DOI: 10.1016/j.neuint.2007.06.006] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2007] [Revised: 06/07/2007] [Accepted: 06/08/2007] [Indexed: 01/04/2023]
Abstract
G protein-coupled receptors (GPCRs) constitute one of the largest families of genes in the human genome, and are the largest targets for drug development. Although a large number of GPCR genes have recently been identified, ligands have not yet been identified for many of them. Various assay systems have been employed to identify ligands for orphan GPCRs, but there is still no simple and general method to screen for ligands of such GPCRs, particularly of G(i)-coupled receptors. We have examined whether fusion proteins of GPCRs with G protein alpha subunit (Galpha) could be utilized for ligand screening and showed that the fusion proteins provide an effective method for the purpose. This article focuses on the followings: (1) characterization of GPCR genes and GPCRs, (2) identification of ligands for orphan GPCRs, (3) characterization of GPCR-Galpha fusion proteins, and (4) identification of ligands for orphan GPCRs using GPCR-Galpha fusion proteins.
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Affiliation(s)
- Hinako Suga
- Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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775
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Koizumi A, Nakajima KI, Asakura T, Morita Y, Ito K, Shmizu-Ibuka A, Misaka T, Abe K. Taste-modifying sweet protein, neoculin, is received at human T1R3 amino terminal domain. Biochem Biophys Res Commun 2007; 358:585-9. [PMID: 17499612 DOI: 10.1016/j.bbrc.2007.04.171] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2007] [Accepted: 04/26/2007] [Indexed: 12/29/2022]
Abstract
This study examines taste reception of neoculin, a Curculigo latifolia sweet protein with taste-modifying activity which converts sourness to sweetness. Neoculin tastes sweet to humans, but not to mice, and is received by the human sweet taste receptor hT1R2-hT1R3. In the present study with calcium imaging analysis of HEK cells expressing human and mouse T1Rs, we demonstrated that hT1R3 is required for the reception of neoculin. Further experiments using human/mouse chimeric T1R3s revealed that the extracellular amino terminal domain (ATD) of hT1R3 is essential for the reception of neoculin. Although T1R2-T1R3 is known to have multiple potential ligand-binding sites to receive a wide variety of sweeteners, the present study is apparently the first to identify the ATD of hT1R3 as a new sweetener-binding region.
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Affiliation(s)
- Ayako Koizumi
- Department of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Tokyo, Japan
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776
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Leseigneur CDC, Verburgt L, Nicolson SW. Whitebellied sunbirds (Nectarinia talatala, Nectariniidae) do not prefer artificial nectar containing amino acids. J Comp Physiol B 2007; 177:679-85. [PMID: 17541603 DOI: 10.1007/s00360-007-0165-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2006] [Revised: 04/25/2007] [Accepted: 04/26/2007] [Indexed: 10/23/2022]
Abstract
Amino acids are the most abundant class of compounds in nectar after sugars. Like its sugar concentration, the amino acid concentration of nectar has been linked to pollinator type, and it has been suggested that amino acid concentrations are high in the floral nectars of plant species pollinated by passerine birds compared to those pollinated by hummingbirds. We investigated the feeding response of whitebellied sunbirds (Nectarinia talatala) to the inclusion of amino acids in artificial nectar (0.63 M sucrose solution). The response to asparagine, glutamine, phenylalanine, proline, serine and valine, amino acids commonly found in floral nectars, was tested individually and using a mixture of all six amino acids, at two different concentrations (2 and 15 mM). Sunbirds showed no significant preference for amino acids in nectar, or avoided them, especially at the higher concentration. We discuss these findings in the light of the nitrogen requirements of nectarivorous birds and data on amino acids in floral nectars.
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Affiliation(s)
- C D C Leseigneur
- Department of Zoology and Entomology, University of Pretoria, Pretoria 0002, South Africa.
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777
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Roper SD. Signal transduction and information processing in mammalian taste buds. PFLUGERS ARCHIV : EUROPEAN JOURNAL OF PHYSIOLOGY 2007. [PMID: 17468883 DOI: 10.1007/s00424‐007‐0247‐x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
The molecular machinery for chemosensory transduction in taste buds has received considerable attention within the last decade. Consequently, we now know a great deal about sweet, bitter, and umami taste mechanisms and are gaining ground rapidly on salty and sour transduction. Sweet, bitter, and umami tastes are transduced by G-protein-coupled receptors. Salty taste may be transduced by epithelial Na channels similar to those found in renal tissues. Sour transduction appears to be initiated by intracellular acidification acting on acid-sensitive membrane proteins. Once a taste signal is generated in a taste cell, the subsequent steps involve secretion of neurotransmitters, including ATP and serotonin. It is now recognized that the cells responding to sweet, bitter, and umami taste stimuli do not possess synapses and instead secrete the neurotransmitter ATP via a novel mechanism not involving conventional vesicular exocytosis. ATP is believed to excite primary sensory afferent fibers that convey gustatory signals to the brain. In contrast, taste cells that do have synapses release serotonin in response to gustatory stimulation. The postsynaptic targets of serotonin have not yet been identified. Finally, ATP secreted from receptor cells also acts on neighboring taste cells to stimulate their release of serotonin. This suggests that there is important information processing and signal coding taking place in the mammalian taste bud after gustatory stimulation.
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Affiliation(s)
- Stephen D Roper
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL 33136, USA.
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778
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Wellendorph P, Burhenne N, Christiansen B, Walter B, Schmale H, Bräuner-Osborne H. The rat GPRC6A: cloning and characterization. Gene 2007; 396:257-67. [PMID: 17478059 DOI: 10.1016/j.gene.2007.03.008] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2006] [Revised: 03/16/2007] [Accepted: 03/16/2007] [Indexed: 11/23/2022]
Abstract
GPRC6A is a novel member of family C of G protein-coupled receptors with so far elusive biological function. GPRC6A has been described in human and mouse as a promiscuous l-alpha-amino acid receptor. We now report the cloning, expression analysis and, functional characterization of the rat orthologue of GPRC6A. Full-length cloning of rat GPRC6A (rGPRC6A) was accomplished using amplification of cDNA from taste tissue, and the identity of rGPRC6A confirmed at both the genomic and the protein level by similarity studies. Using selective primers, reverse transcriptase polymerase chain reaction showed that the mRNA is widely but weakly distributed, except for a high expression in the soft palate, the so-called geschmacksstreifen. On the protein level, rGPRC6A was shown to be glycosylated and most likely oligomeric, and using immunochemistry we observed that rGPRC6A is expressed at the plasma membrane of mammalian cell lines. Utilizing co-expression of rGPRC6A and the promiscuous Galpha(q)(G66D) protein in an engineered cell-based inositol phosphate turnover assay, we were able to study the ligand profile of the receptor. We found that l-ornithine is the most potent and efficacious l-amino acid agonist with an EC(50) value of 264 microM, followed by several other aliphatic, neutral, and basic amino acids. Furthermore, the divalent cation Mg(2+) was found to be a positive modulator of the l-ornithine response. The presented quantitative pharmacological data underlines the evolutionary conservation of GPRC6A to the rat and signifies the physiological importance and emerging pharmacological potential of GPRC6A.
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Affiliation(s)
- Petrine Wellendorph
- Department of Medicinal Chemistry, Faculty of Pharmaceutical Sciences, University of Copenhagen, Universitetsparken 2, DK-2100 Copenhagen, Denmark.
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779
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Schiffman SS, Sattely-Miller EA, Bishay IE. Time to maximum sweetness intensity of binary and ternary blends of sweeteners. Food Qual Prefer 2007. [DOI: 10.1016/j.foodqual.2006.04.007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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780
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Pin JP, Neubig R, Bouvier M, Devi L, Filizola M, Javitch JA, Lohse MJ, Milligan G, Palczewski K, Parmentier M, Spedding M. International Union of Basic and Clinical Pharmacology. LXVII. Recommendations for the Recognition and Nomenclature of G Protein-Coupled Receptor Heteromultimers. Pharmacol Rev 2007; 59:5-13. [PMID: 17329545 DOI: 10.1124/pr.59.1.5] [Citation(s) in RCA: 204] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
G protein-coupled receptors (GPCRs) have long been considered to be monomeric membrane proteins. Although numerous recent studies have indicated that GPCRs can form multimeric complexes, the functional and pharmacological consequences of this phenomenon have remained elusive. With the discovery that the functional GABA(B) receptor is an obligate heterodimer and with the use of energy transfer technologies, it is now accepted that GPCRs can form heteromultimers. In some cases, specific properties of such heteromers not shared by their respective homomers have been reported. Although in most cases these properties have only been observed in heterologous expression systems, there are a few reports describing data consistent with such heteromultimeric GPCR complexes also existing in native tissues. The present article illustrates well-documented examples of such native multimeric complexes, lists a number of recommendations for recognition and acceptance of such multimeric receptors, and gives recommendations for their nomenclature.
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Affiliation(s)
- Jean-Philippe Pin
- Institut de Génomique Fonctionnelle, 141, rue de la Cardonille, 34094 Montpellier cedex 5, France.
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781
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San Gabriel AM, Maekawa T, Uneyama H, Yoshie S, Torii K. mGluR1 in the fundic glands of rat stomach. FEBS Lett 2007; 581:1119-23. [PMID: 17331504 DOI: 10.1016/j.febslet.2007.02.016] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2006] [Revised: 02/07/2007] [Accepted: 02/07/2007] [Indexed: 11/18/2022]
Abstract
l-glutamate not only confers cognitive discrimination for umami taste in the oral cavity, but also conveys sensory information to vagal afferent fibers in the gastric mucosa. We used RT-PCR, western blotting, and immunohistochemistry to demonstrate that mGluR1 is located in glandular stomach. Double staining revealed that mGluR1 is found at the apical membrane of chief cells and possibly in parietal cells. Moreover, a diet with 1% l-glutamate induced changes in the expression of pepsinogen C mRNA in stomach mucosa. These data suggest that mGluR1 is involved in the gastric phase regulation of protein digestion.
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Affiliation(s)
- Ana M San Gabriel
- Physiology and Nutrition Group, Institute of Life Sciences, Ajinomoto Co. Inc., Kawasaki 210-8681, Japan.
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782
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Levoye A, Dam J, Ayoub MA, Guillaume JL, Jockers R. Do orphan G-protein-coupled receptors have ligand-independent functions? New insights from receptor heterodimers. EMBO Rep 2007; 7:1094-8. [PMID: 17077864 PMCID: PMC1679777 DOI: 10.1038/sj.embor.7400838] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2006] [Accepted: 09/15/2006] [Indexed: 11/08/2022] Open
Abstract
G-protein-coupled receptors (GPCRs) are important drug targets and are involved in virtually every biological process. However, there are still more than 140 orphan GPCRs, and deciphering their function remains a priority for fundamental and clinical research. Research on orphan GPCRs has concentrated mainly on the identification of their natural ligands, whereas recent data suggest additional ligand-independent functions for these receptors. This emerging concept is connected with the observation that orphan GPCRs can heterodimerize with GPCRs that have identified ligands, and by so doing regulate the function of the latter. Pairing orphan GPCRs with their potential heterodimerization partners will have a major impact on our understanding of the extraordinary diversity offered by GPCR heterodimerization and, in addition, will constitute a novel strategy to elucidate the function of orphan receptors that needs to be added to the repertoire of 'deorphanization' strategies.
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Affiliation(s)
- Angélique Levoye
- Institut Cochin, Department of Cell Biology, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Inserm, U567, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- CNRS, UMR 8104, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Université Paris Descartes, Faculté de Médecine René Descartes, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- These authors contributed equally to this work
| | - Julie Dam
- Institut Cochin, Department of Cell Biology, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Inserm, U567, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- CNRS, UMR 8104, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Université Paris Descartes, Faculté de Médecine René Descartes, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- These authors contributed equally to this work
| | - Mohammed A Ayoub
- Institut Cochin, Department of Cell Biology, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Inserm, U567, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- CNRS, UMR 8104, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Université Paris Descartes, Faculté de Médecine René Descartes, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Present address: Institut de Génomique Fonctionnelle (IGF), UMR5203 CNRS, U661 INSERM, Universités Montpellier 1 & 2, Département de Pharmacologie Moléculaire, 141 rue de la Cardonille 34094, Montpellier Cedex 05, France
| | - Jean-Luc Guillaume
- Institut Cochin, Department of Cell Biology, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Inserm, U567, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- CNRS, UMR 8104, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Université Paris Descartes, Faculté de Médecine René Descartes, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
| | - Ralf Jockers
- Institut Cochin, Department of Cell Biology, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Inserm, U567, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- CNRS, UMR 8104, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Université Paris Descartes, Faculté de Médecine René Descartes, UMR-S 8104, 22 rue Méchain, Paris F-75014, France
- Tel: +33 1 40 51 64 34; Fax: +33 1 40 51 64 30;
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783
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Young SF, Griffante C, Aguilera G. Dimerization between vasopressin V1b and corticotropin releasing hormone type 1 receptors. Cell Mol Neurobiol 2007; 27:439-61. [PMID: 17318384 DOI: 10.1007/s10571-006-9135-8] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2006] [Accepted: 12/19/2006] [Indexed: 11/26/2022]
Abstract
1. Increasing evidence indicates that guanyl protein coupled receptors (GPCRs), including members of the vasopressin (VP) receptor family can act as homo- and heterodimers. Regulated expression and interaction of pituitary VP V1b receptor (V1bR) and corticotropin releasing hormone receptor type 1 (CRHR1) are critical for hypothalamic pituitary adrenal (HPA) axis adaptation, but it is unknown whether this involves physical interaction between these receptors.2. Bioluminescence resonance energy transfer (BRET) experiments using V1bR and CRHR1 fused to either Renilla luciferase (Rluc) or yellow fluorescent protein (YFP) at the N-terminus, but not the carboxyl-terminus, revealed specific interaction (BRET(50) = 0.39 +/- 0.08, V1bR) that was inhibited by untagged V1b or CRHR1 receptors, suggesting homo- and heterodimerization. The BRET data were confirmed by coimmunoprecipitation experiments using fully bioactive receptors tagged at the aminoterminus with c-myc and Flag epitopes, demonstrating specific homodimerization of the V1b receptor and heterodimerization of the V1b receptor with CRHR1 receptors.3. Heterodimerization between V1bR and CRHR1 is not ligand dependent since stimulation with CRH and AVP had no effect on coimmunoprecipitation. In membranes obtained from cells cotransfected with CRHR1 and V1bR, incubation with the heterologous nonpeptide antagonist did not alter the binding affinity or capacity of the receptor.4. The data demonstrate that V1bR and CRHR1 can form constitutive homo- and heterodimers and suggests that the heterodimerization does not influence the binding properties of these receptors.
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Affiliation(s)
- Sharla F Young
- Section on Endocrine Physiology, Developmental Endocrinology Branch, National Institute of Child Health and Human Development/NIH, CRC/1-3330, 10 Center Drive, MSC 1103, Bethesda, MD 20892-1103, USA
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784
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785
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Simon SA, de Araujo IE, Gutierrez R, Nicolelis MAL. The neural mechanisms of gustation: a distributed processing code. Nat Rev Neurosci 2007; 7:890-901. [PMID: 17053812 DOI: 10.1038/nrn2006] [Citation(s) in RCA: 186] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Whenever food is placed in the mouth, taste receptors are stimulated. Simultaneously, different types of sensory fibre that monitor several food attributes such as texture, temperature and odour are activated. Here, we evaluate taste and oral somatosensory peripheral transduction mechanisms as well as the multi-sensory integrative functions of the central pathways that support the complex sensations that we usually associate with gustation. On the basis of recent experimental data, we argue that these brain circuits make use of distributed ensemble codes that represent the sensory and post-ingestive properties of tastants.
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Affiliation(s)
- Sidney A Simon
- Department of Neurobiology, Duke University, Durham, North Carolina 27710, USA.
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786
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Sugino H. Comparative genomic analysis of the mouse and rat amylase multigene family. FEBS Lett 2007; 581:355-60. [PMID: 17223109 DOI: 10.1016/j.febslet.2006.12.039] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2006] [Revised: 12/21/2006] [Accepted: 12/22/2006] [Indexed: 11/21/2022]
Abstract
The rat and mouse amylase gene families were characterized using sequence data from the UCSC genome assembly. We found that the rat genome contains one amylase-1 and two amylase-2 genes, lying close to one another on the same chromosome. Detailed analysis revealed at least six additional amylase pseudogenes in the rat genome in the region adjacent to the amylase-2 genes. In contrast, the mouse has one amylase-1 gene and five amylase-2 genes; the latter are tandemly and systematically arranged on the same chromosome and were generated by segmental duplication. Detailed analysis revealed that the mouse has two amylase pseudogenes, located 5' to the five amylase-2 segments. Thus, the amylase genes of mouse and rat tend to be amplified; the sequences of some of them are fixed while others have become pseudogenes during evolution. This is the second report of amylase genomic organization in mammals and the first in the rodents.
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Affiliation(s)
- Hidehiko Sugino
- Laboratories for Integrated Biology, Graduate School of Frontier Biosciences, Osaka University, 1-3 Suita, Osaka 565-0871, Japan.
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787
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Christiansen B, Wellendorph P, Bräuner-Osborne H. Known regulators of nitric oxide synthase and arginase are agonists at the human G-protein-coupled receptor GPRC6A. Br J Pharmacol 2007; 147:855-63. [PMID: 16491104 PMCID: PMC1760712 DOI: 10.1038/sj.bjp.0706682] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
GPRC6A is a novel family C G-protein-coupled receptor (GPCR) with so far unknown physiological function. It was the aim of our study to further characterize the ligand preferences of the receptor and elucidate structural requirements for activity. We have previously generated a functional chimeric receptor construct, h6A/5.24, containing the ligand-binding amino-terminal domain of the human GPRC6A and the seven-transmembrane domain and carboxy terminus of the homologous goldfish receptor 5.24. Based on knowledge that this chimera prefers basic L-alpha-amino acids such as arginine, lysine and ornithine, we searched for commercially available analogues of these and other L-alpha-amino acids, and tested them for activity in a fluorescence-based calcium assay. The majority of the tested compounds are involved in the regulation of nitric oxide synthase (NOS) and arginase enzymes. Altogether we profiled 30 different analogues. We found that a structurally wide range of L-alpha-amino-acid analogues of both arginine, lysine, and ornithine are agonists at h6A/5.24, whereas no antagonists were identified. From the profiling it is concluded that L-alpha-amino acids containing a highly basic side chain confer the highest activity, although the most potent compound was only twice as potent as L-arginine, which has a EC50 value of 23.5 microM. The reported agonism of NOS- and arginase-active compounds at GPRC6A has obvious implications in interpretation of experiments involving the NOS and arginase systems, and interfering effects at GPRC6A should be regarded of relevance, especially as the physiological function of the receptor is not yet understood.
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Affiliation(s)
- Bolette Christiansen
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, Copenhagen DK-2100, Denmark
| | - Petrine Wellendorph
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, Copenhagen DK-2100, Denmark
| | - Hans Bräuner-Osborne
- Department of Medicinal Chemistry, The Danish University of Pharmaceutical Sciences, 2 Universitetsparken, Copenhagen DK-2100, Denmark
- Author for correspondence:
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788
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Abstract
The emerging picture of taste coding at the periphery is one of elegant simplicity. Contrary to what was generally believed, it is now clear that distinct cell types expressing unique receptors are tuned to detect each of the five basic tastes: sweet, sour, bitter, salty and umami. Importantly, receptor cells for each taste quality function as dedicated sensors wired to elicit stereotypic responses.
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Affiliation(s)
- Jayaram Chandrashekar
- Howard Hughes Medical Institute and Departments of Neurobiology and Neurosciences, University of California at San Diego, La Jolla, California 92093-0649, USA
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789
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Parmentier M, Detheux M. Deorphanization of G-Protein-Coupled Receptors. ERNST SCHERING FOUNDATION SYMPOSIUM PROCEEDINGS 2007:163-86. [PMID: 17703582 DOI: 10.1007/2789_2006_008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
G-protein-coupled receptors constitute one of the major families of drug targets. Orphan receptors, for which the ligands and function are still unknown, are an attractive set of future targets for presently unmet medical needs. Screening strategies have been developed over the years in order to identify the natural ligands of these receptors. Natural or chimeric G-proteins that can redirect the natural coupling of receptors toward intracellular calcium release are frequently used. Potential problems include poor expression or trafficking to the cell surface, constitutive activity of the receptors, or the presence of endogenous receptors in the cell types used for functional expression, leading to nonspecific responses. Many orphan receptors characterized over the last 10 years have been associated with previously known bioactive molecules. However, new and unpredicted biological mediators have also been purified from complex biological sources. A few old and recent examples, including nociceptin, chemerin, and the F2L peptide are illustrated. Future challenges for the functional characterization of the remaining orphan receptors include the potential requirement of specific proteins necessary for quality control, trafficking or coupling of specific receptors, the possible formation of obligate heterodimers, and the possibility that some constitutively active receptors may lack ligands or respond only to inverse agonists. Adapted expression and screening strategies will be needed to deal with these issues.
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Affiliation(s)
- M Parmentier
- IRIBHN, ULB Campus Erasme, 808 roude de Lennik, 1070 Bruxelles, Belgium.
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790
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Choi S, Lee M, Shiu AL, Yo SJ, Aponte GW. Identification of a protein hydrolysate responsive G protein-coupled receptor in enterocytes. Am J Physiol Gastrointest Liver Physiol 2007; 292:G98-G112. [PMID: 16935853 DOI: 10.1152/ajpgi.00295.2006] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
G protein-coupled receptors (GPCRs) have the potential to play a role as molecular sensors responsive to luminal dietary contents. Although such a role for GPCRs has been implicated in the intestinal response to protein hydrolysate, no GPCR directly involved in this process has been previously identified. In the present study, for the first time, we identified GPR93 expression in enterocytes and demonstrated its activation in these cells by protein hydrolysate with EC50 of 10.6 mg/ml as determined by the induction of intracellular free Ca2+. In enterocytes, GPR93 was synergistically activated by protein hydrolysate in combination with an agonist, oleoyl-l-alpha-lysophosphatidic acid (LPA), which activated the receptor in these enterocytes with EC50 of 7.9 nM. The increased intracellular Ca2+ by GPR93 activation was observed without the addition of a promiscuous Galpha protein and was pertussis toxin sensitive, which suggests Galpha(q)- and Galpha(i)-mediated pathways. Activated GPR93 also induced pertussis toxin-sensitive ERK1/2 phosphorylation. Both nuclear factor of activated T cells and 12-O-tetradecanoylphorbol 13-acetate responsive elements reporter activities were induced by protein hydrolysate in cells exogenously expressing GPR93. The peptidomimetic cefaclor by itself did not activate GPR93 but potentiated the protein hydrolysate response and further amplified the synergistic enhancement of GPR93 activation by protein hydrolysate and LPA. These data suggest that, physiologically, the composition of stimuli might determine GPR93 activity or its sensitivity toward a given activator and suggest a new mechanism of the regulation of mucosal cell proliferation and differentiation and hormonal secretion by dietary products in the lumen.
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Affiliation(s)
- Sungwon Choi
- Department of Nutritional Sciences and Toxicology, University of California at Berkeley, Berkeley, CA 94720-3104, USA
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791
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Matsumura S, Mizushige T, Yoneda T, Iwanaga T, Tsuzuki S, Inoue K, Fushiki T. GPR expression in the rat taste bud relating to fatty acid sensing. Biomed Res 2007; 28:49-55. [PMID: 17379957 DOI: 10.2220/biomedres.28.49] [Citation(s) in RCA: 138] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
We investigated the expression of G protein-coupled receptor GPR40 and GPR120 in the rat tongue. Using reverse transcription polymerase chain reaction, we detected a significant expression of GPR120 mRNA in the epithelium of the circumvallate papillae but not in the nonsensory epithelium, while the expression of GPR40 mRNA was undetectable in the sensory papillae. Western blotting analysis of colon and circumvallate papillae for GPR120 showed a protein band with a molecular weight that corresponds to that of GPR120, indicating that this antibody could recognize a native form of GPR120. Immunohistochemistry using anti-GPR120 antibody revealed GPR120 immunoreactivity in the enteroendocrine cells of the colon. Furthermore, some cells in each taste bud were stained positively with more intense labeling in the apical part of the cells. These results suggested that GPR120 is expressed in the taste cells of the circumvallate papillae to sense dietary fat, like the receptor expressed in the enteroendocrine cells.
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Affiliation(s)
- Shigenobu Matsumura
- Laboratory of Nutrition Chemistry, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Oiwakecho, Kitashirakawa, Japan
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792
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The repertoire of olfactory C family G protein-coupled receptors in zebrafish: candidate chemosensory receptors for amino acids. BMC Genomics 2006; 7:309. [PMID: 17156446 PMCID: PMC1764893 DOI: 10.1186/1471-2164-7-309] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2006] [Accepted: 12/08/2006] [Indexed: 11/22/2022] Open
Abstract
Background Vertebrate odorant receptors comprise at least three types of G protein-coupled receptors (GPCRs): the OR, V1R, and V2R/V2R-like receptors, the latter group belonging to the C family of GPCRs. These receptor families are thought to receive chemosensory information from a wide spectrum of odorant and pheromonal cues that influence critical animal behaviors such as feeding, reproduction and other social interactions. Results Using genome database mining and other informatics approaches, we identified and characterized the repertoire of 54 intact "V2R-like" olfactory C family GPCRs in the zebrafish. Phylogenetic analysis – which also included a set of 34 C family GPCRs from fugu – places the fish olfactory receptors in three major groups, which are related to but clearly distinct from other C family GPCRs, including the calcium sensing receptor, metabotropic glutamate receptors, GABA-B receptor, T1R taste receptors, and the major group of V2R vomeronasal receptor families. Interestingly, an analysis of sequence conservation and selective pressure in the zebrafish receptors revealed the retention of a conserved sequence motif previously shown to be required for ligand binding in other amino acid receptors. Conclusion Based on our findings, we propose that the repertoire of zebrafish olfactory C family GPCRs has evolved to allow the detection and discrimination of a spectrum of amino acid and/or amino acid-based compounds, which are potent olfactory cues in fish. Furthermore, as the major groups of fish receptors and mammalian V2R receptors appear to have diverged significantly from a common ancestral gene(s), these receptors likely mediate chemosensation of different classes of chemical structures by their respective organisms.
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793
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Uneyama H, Niijima A, San Gabriel A, Torii K. Luminal amino acid sensing in the rat gastric mucosa. Am J Physiol Gastrointest Liver Physiol 2006; 291:G1163-70. [PMID: 16809638 DOI: 10.1152/ajpgi.00587.2005] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Recent advancements in molecular biology in the field of taste perception in the oral cavity have raised the possibility for ingested nutrients to be "tasted" in the upper gastrointestinal tract. The purpose of this study was to identify the existence of a nutrient-sensing system by the vagus in the rat stomach. Afferent fibers of the gastric branch increased their firing rate solely with the intragastric application of the amino acid glutamate. Other amino acids failed to have the same effect. This response to glutamate was blocked by the depletion of serotonin (5-HT) and inhibition of serotonin receptor(3) (5-HT(3)) or nitric oxide (NO) synthase enzyme. Luminal perfusion with the local anesthesia lidocaine abolished the glutamate-evoked afferent activation. The afferent response was also mimicked by luminal perfusion with a NO donor, sodium nitroprusside. In addition, the NO donor-induced afferent activation was abolished by 5-HT(3) blockade as well. Altogether, these results strongly suggest the existence of a sensing system for glutamate in the rat gastric mucosa. Thus luminal glutamate would enhance the electrophysiological firing rate of afferent fibers from the vagus nerve of the stomach through the production of mucosal bioactive substances such as NO and 5-HT. Assuming there is a universal coexistence of free glutamate with dietary protein, a glutamate-sensing system in the stomach could contribute to the gastric phase of protein digestion.
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Affiliation(s)
- Hisayuki Uneyama
- Physiology and Nutrition Group, Institute of Life Sciences, Ajinomoto Co., Inc., 1-1 Suzuki-cho, Kawasaki-ku, Kawasaki 210-8681, Japan.
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794
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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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795
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796
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Conigrave AD, Hampson DR. Broad-spectrum L-amino acid sensing by class 3 G-protein-coupled receptors. Trends Endocrinol Metab 2006; 17:398-407. [PMID: 17085057 DOI: 10.1016/j.tem.2006.10.012] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/31/2006] [Revised: 10/04/2006] [Accepted: 10/24/2006] [Indexed: 01/24/2023]
Abstract
The sensing of nutrients is essential to the control of growth and metabolism. Although the sensing mechanisms responsible for the detection and coordination of metabolic responses to some nutrients, most notably glucose, are well understood, the molecular basis of amino acid sensing by cells and tissues is only now emerging. In this article, we consider evidence that some members of G-protein-coupled receptor class 3 are broad-spectrum amino acid sensors that couple changes in extracellular amino acid levels to the activation of intracellular signaling pathways. In particular, we consider both the molecular basis of specific and broad-spectrum amino acid sensing by different members of class 3 and the physiological significance of broad spectrum amino acid sensing by the extracellular calcium-sensing receptor, heterodimeric taste receptors and the recently "deorphanized" receptor GPRC6A and its goldfish homolog, the 5.24 chemoreceptor.
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Affiliation(s)
- Arthur D Conigrave
- School of Molecular and Microbial Biosciences, University of Sydney, NSW 2006, Australia.
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797
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Rozengurt N, Wu SV, Chen MC, Huang C, Sternini C, Rozengurt E. Colocalization of the alpha-subunit of gustducin with PYY and GLP-1 in L cells of human colon. Am J Physiol Gastrointest Liver Physiol 2006; 291:G792-802. [PMID: 16728727 DOI: 10.1152/ajpgi.00074.2006] [Citation(s) in RCA: 212] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
In view of the importance of molecular sensing in the function of the gastrointestinal (GI) tract, we assessed whether signal transduction proteins that mediate taste signaling are expressed in cells of the human gut. Here, we demonstrated that the alpha-subunit of the taste-specific G protein gustducin (Galpha(gust)) is expressed prominently in cells of the human colon that also contain chromogranin A, an established marker of endocrine cells. Double-labeling immunofluorescence and staining of serial sections demonstrated that Galpha(gust) localized to enteroendocrine L cells that express peptide YY and glucagon-like peptide-1 in the human colonic mucosa. We also found expression of transcripts encoding human type 2 receptor (hT2R) family members, hT1R3, and Galpha(gust) in the human colon and in the human intestinal endocrine cell lines (HuTu-80 and NCI-H716 cells). Stimulation of HuTu-80 or NCI-H716 cells with the bitter-tasting compound phenylthiocarbamide, which binds hT2R38, induced a rapid increase in the intracellular Ca2+ concentration in these cells. The identification of Galpha(gust) and chemosensory receptors that perceive chemical components of ingested substances, including drugs and toxins, in open enteroendocrine L cells has important implications for understanding molecular sensing in the human GI tract and for developing novel therapeutic compounds that modify the function of these receptors in the gut.
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Affiliation(s)
- Nora Rozengurt
- Department of Pathology, David Geffen School of Medicine, University of California-Los Angeles, 900 Veteran Ave., Warren Hall Rm. 11-115, Los Angeles, CA 90095-1786, USA.
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798
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Bezençon C, le Coutre J, Damak S. Taste-signaling proteins are coexpressed in solitary intestinal epithelial cells. Chem Senses 2006; 32:41-9. [PMID: 17030556 DOI: 10.1093/chemse/bjl034] [Citation(s) in RCA: 288] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The taste system, made up of taste receptor cells clustered in taste buds at the surface of the tongue and the soft palate, plays a key role in the decision to ingest or reject food and thereby is essential in protecting organisms against harmful toxins and in selecting the most appropriate nutrients. To determine if a similar chemosensory system exists in the gastrointestinal tract, we used immunohistochemistry and real-time polymerase chain reaction (PCR) to investigate which taste-signaling molecules are expressed in the intestinal mucosa. The PCR data showed that T1r1, T1r2, T1r3, alpha-gustducin, phospholipase Cbeta2 (PLCbeta2), and Trpm5 are expressed in the stomach, small intestine, and colon of mice and humans, with the exception of T1r2, which was not detected in the mouse and human stomach or in the mouse colon. Using transgenic mice expressing enhanced green fluorescent protein under the control of the Trpm5 promoter, we found colocalization of Trpm5 and alpha-gustducin in tufted cells at the surface epithelium of the colon, but these cells did not express T1r3 or PLCbeta2. In the duodenal glands, 43%, 33%, and 38% of Trpm5-expressing cells also express PLCbeta2, T1r3, or alpha-gustducin, respectively. The duodenal gland cells that coexpress PLCbeta2 and Trpm5 morphologically resemble enteroendocrine cells. We found a large degree of colocalization of Trpm5, alpha-gustducin, T1r1, and T1r3 in tufted cells of the duodenal villi, but these cells rarely expressed PLCbeta2. The data suggest that these duodenal cells are possibly involved in sensing amino acids.
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Affiliation(s)
- Carole Bezençon
- Nestlé Research Center, Vers-chez-les-Blanc, Lausanne, Switzerland
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799
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Huang AL, Chen X, Hoon MA, Chandrashekar J, Guo W, Tränkner D, Ryba NJP, Zuker CS. The cells and logic for mammalian sour taste detection. Nature 2006; 442:934-8. [PMID: 16929298 PMCID: PMC1571047 DOI: 10.1038/nature05084] [Citation(s) in RCA: 517] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2006] [Accepted: 07/19/2006] [Indexed: 01/05/2023]
Abstract
Mammals taste many compounds yet use a sensory palette consisting of only five basic taste modalities: sweet, bitter, sour, salty and umami (the taste of monosodium glutamate). Although this repertoire may seem modest, it provides animals with critical information about the nature and quality of food. Sour taste detection functions as an important sensory input to warn against the ingestion of acidic (for example, spoiled or unripe) food sources. We have used a combination of bioinformatics, genetic and functional studies to identify PKD2L1, a polycystic-kidney-disease-like ion channel, as a candidate mammalian sour taste sensor. In the tongue, PKD2L1 is expressed in a subset of taste receptor cells distinct from those responsible for sweet, bitter and umami taste. To examine the role of PKD2L1-expressing taste cells in vivo, we engineered mice with targeted genetic ablations of selected populations of taste receptor cells. Animals lacking PKD2L1-expressing cells are completely devoid of taste responses to sour stimuli. Notably, responses to all other tastants remained unaffected, proving that the segregation of taste qualities even extends to ionic stimuli. Our results now establish independent cellular substrates for four of the five basic taste modalities, and support a comprehensive labelled-line mode of taste coding at the periphery. Notably, PKD2L1 is also expressed in specific neurons surrounding the central canal of the spinal cord. Here we demonstrate that these PKD2L1-expressing neurons send projections to the central canal, and selectively trigger action potentials in response to decreases in extracellular pH. We propose that these cells correspond to the long-sought components of the cerebrospinal fluid chemosensory system. Taken together, our results suggest a common basis for acid sensing in disparate physiological settings.
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Affiliation(s)
- Angela L. Huang
- Howard Hughes Medical Institute and Departments of Neurobiology and Neurosciences, University of California at San Diego, La Jolla, California 92093-0649, USA
| | - Xiaoke Chen
- Howard Hughes Medical Institute and Departments of Neurobiology and Neurosciences, University of California at San Diego, La Jolla, California 92093-0649, USA
| | - Mark A. Hoon
- National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Jayaram Chandrashekar
- Howard Hughes Medical Institute and Departments of Neurobiology and Neurosciences, University of California at San Diego, La Jolla, California 92093-0649, USA
| | - Wei Guo
- Howard Hughes Medical Institute and Departments of Neurobiology and Neurosciences, University of California at San Diego, La Jolla, California 92093-0649, USA
| | - Dimitri Tränkner
- Howard Hughes Medical Institute and Departments of Neurobiology and Neurosciences, University of California at San Diego, La Jolla, California 92093-0649, USA
| | - Nicholas J. P. Ryba
- National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, Maryland 20892, USA
| | - Charles S. Zuker
- Howard Hughes Medical Institute and Departments of Neurobiology and Neurosciences, University of California at San Diego, La Jolla, California 92093-0649, USA
- *correspondence to
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800
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Scinska-Bienkowska A, Wrobel E, Turzynska D, Bidzinski A, Jezewska E, Sienkiewicz-Jarosz H, Golembiowska K, Kostowski W, Kukwa A, Plaznik A, Bienkowski P. Glutamate concentration in whole saliva and taste responses to monosodium glutamate in humans. Nutr Neurosci 2006; 9:25-31. [PMID: 16910167 DOI: 10.1080/10284150600621964] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
It is universally accepted that saliva plays an important role in taste sensations. However, interactions between constituents of whole saliva and the five basic taste modalities are still poorly understood. The aim of the present study was to evaluate possible relationship between endogenous glutamate (Glu) levels in whole saliva and taste responses to a prototypic umami substance, monosodium glutamate (MSG; 0.03-10.0%). Rated intensity and pleasantness of MSG taste was studied in healthy volunteers divided into a high glutamate (HG) in saliva (HG; n = 19) and low glutamate in saliva (LG; n = 18) group based on the median split level of salivary Glu. The HG and LG group did not differ in terms of electrogustometric thresholds, rated intensity of the MSG samples and pleasantness of distilled water and the lower MSG concentrations (0.03-1.0%). Perceived intensity of water taste was significantly (P < 0.05) higher in the LG subjects. The LG group rated the higher MSG concentrations (3.0-10.0%) as more unpleasant (P < 0.01). The difference remained significant after controlling for a between-group difference in age. The present results suggest that individual differences in salivary Glu levels may alter hedonic responses to suprathreshold MSG concentrations.
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