Taste of glutamate salts in young and elderly subjects: Role of inosine 5′-monophosphate and ions

Schiffman, Susan S.; Frey, Amy E; Luboski, J.A.; Foster, Mark; Erickson, Robert P.

doi:10.1016/0031-9384(91)90193-r

Cited by 51 publications

(34 citation statements)

References 17 publications

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“…Taste Tests. Detection threshold effects of lactisole on umami, sweet, and salt taste were determined by tasting dilution series of these taste stimuli in the presence and absence of lactisole as described (11). Detection threshold values were averaged over four trials for three subjects.…”

Section: Methodsmentioning

confidence: 99%

Different functional roles of T1R subunits in the heteromeric taste receptors

Staszewski

Tang

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

452

441

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The T1R receptors, a family of taste-specific class C G proteincoupled receptors, mediate mammalian sweet and umami tastes. The structure-function relationships of T1R receptors remain largely unknown. In this study, we demonstrate the different functional roles of T1R extracellular and transmembrane domains in ligand recognition and G protein coupling. Similar to other family C G protein-coupled receptors, the N-terminal Venus flytrap domain of T1R2 is required for recognizing sweeteners, such as aspartame and neotame. The G protein coupling requires the transmembrane domain of T1R2. Surprisingly, the C-terminal transmembrane domain of T1R3 is required for recognizing sweetener cyclamate and sweet taste inhibitor lactisole. Because T1R3 is the common subunit in the sweet taste receptor and the umami taste receptor, we tested the interaction of lactisole and cyclamate with the umami taste receptor. A family of class C G protein-coupled receptors (GPCRs), T1Rs, is selectively expressed in the taste buds (1-6). Functional expression of T1Rs in human embryonic kidney (HEK)-293 cells revealed that different combinations of T1Rs respond to sweet and umami taste stimuli (6, 7). T1R2 and T1R3, when coexpressed in HEK-293 cells, recognize diverse natural and synthetic sweeteners. Similarly, T1R1 and T1R3, when coexpressed in HEK-293 cells, respond to the umami taste stimulus L-glutamate. This response is enhanced by 5Ј ribonucleotides, a hallmark of umami taste. Recent experiments with knockout mice confirmed that T1Rs indeed mediate mouse sweet and umami tastes (8, 9).The class C GPCRs possess a large N-terminal extracellular domain, often referred to as the Venus flytrap domain (10), and are known to function as either homodimers, in the cases of metabotropic glutamate receptors (mGluRs) and calciumsensing receptor, or heterodimers, in the case of ␥-aminobutyric acid type B receptor (GABA B R) (10). The functional expression data suggest a heterodimer mechanism for T1Rs: both T1R1 and T1R2 need to be coexpressed with T1R3 to be functional, which is supported by the overlapping expression patterns of T1Rs in rodent tongue. Nonetheless, there has been no direct evidence that T1Rs function as heteromeric complexes. It is possible that T1R3 is not a functional component of sweet and umami taste receptors, but merely a chaperone protein, which facilitates the proper folding or intracellular translocation of T1R1 and T1R2. The distinct ligand specificities of T1R1͞T1R3 and T1R2͞T1R3 receptors suggest that T1R1 and T1R2 play more important roles in ligand binding in sweet and umami taste receptors than T1R3. Support for this hypothesis was provided recently by results from mouse genetics where human T1R2 transgenic mice, generated on the T1R2 knockout background, displayed sweetener taste preferences similar to those of humans (9). However, the functional role of T1R3 and the overall structure͞function relationship of T1R taste receptors remain largely unknown.Another intriguing observation about the T1R2͞T1R3 receptor is th...

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Section: Methodsmentioning

confidence: 99%

Different functional roles of T1R subunits in the heteromeric taste receptors

Staszewski

Tang

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

452

441

View full text Add to dashboard Cite

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“…In the elderly, elevation of the gustatory threshold for umami taste, as well as for salty, sweet, sour, and bitter tastes, has been confirmed. [1][2][3] Glutamate (Glu), one of non-essential amino acids, has umami taste, and it has been reported that the oral stimulation by MSG solution (umami) increases secretion of saliva and promotes mastication, 4) and activation of the efferent pathways of the gastric and pancreatic vagal rami to facilitate gastric and pancreatic functions and to increase gastric endocrine and pancreatic exocrine and endocrine secretions (pancreatic digestive enzymes, insulin, etc.). 5) Uneyama et al reported that, among 20 amino acids, only Glu can induce afferent reactions of gastric vagal rami and thereby influence digestion/absorption and activation of metabolism after absorption of nutrients through stimulation of the brain via gastric Glu sensors.…”

Section: Introductionmentioning

confidence: 99%

A Possible Application of Monosodium Glutamate to Nutritional Care for Elderly People

Toyama

Tomoe²,

Inoue³

et al. 2008

Biological & Pharmaceutical Bulletin

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Recently, it has been clarified that glutamate (Glu) can stimulate the umami taste as well as the visceral sensation to help the gastric protein digestion. Our survey suggests the possibility that the amount of free Glu in hospital foods is lower than that in ordinary foods. In the present study, monosodium glutamate (MSG) was supplemented to meals for 11 elderly inpatients during 2 months, and the fortification effects on their nutritional status, general condition, and quality of life (QOL) were investigated. The degree of recognition was improved, and peripheral lymphocytes were increased, even when there was no change in nutritional intake or protein nutritional status. Based on these results, we concluded that appropriate utilization of Glu for nutritional care of the elderly people would be useful for improving QOL.

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“…Detection threshold values were determined following the methods of Schiffman et al (14) and averaged over three trials for four subjects.…”

mentioning

confidence: 99%

Human receptors for sweet and umami taste

Staszewski

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

1,243

1,091

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The three members of the T1R class of taste-specific G proteincoupled receptors have been hypothesized to function in combination as heterodimeric sweet taste receptors. Here we show that human T1R2͞T1R3 recognizes diverse natural and synthetic sweeteners. In contrast, human T1R1͞T1R3 responds to the umami taste stimulus L-glutamate, and this response is enhanced by 5-ribonucleotides, a hallmark of umami taste. The ligand specificities of rat T1R2͞T1R3 and T1R1͞T1R3 correspond to those of their human counterparts. These findings implicate the T1Rs in umami taste and suggest that sweet and umami taste receptors share a common subunit. Large-scale sequencing of a subtracted cDNA library derived from rat taste tissue identified a new C-family G proteincoupled receptor, T1R1, that is expressed selectively in taste receptor cells; T1R1-based degenerate PCR led to the identification of a related taste-specific receptor, T1R2 (1). Recently, a third and possibly final member of the T1R family, T1R3, was identified in the human DNA databank (2-7). Tellingly, mouse T1R3 maps to a genomic interval containing Sac, a locus that influences sweet taste in the mouse (8, 9). Recent highresolution genetic mapping and complementation studies have strengthened the connection between mouse T1R3 and Sac (2-7). Although T1R1 and T1R2 appear to be expressed in predominantly nonoverlapping regions of the tongue, they each are coexpressed with T1R3 (1, 3, 4, 6). These overlapping expression patterns and precedent from the structurally related heterodimeric ␥-aminobutyric acid type B receptor (10-13) suggested that T1R1 and T1R2 may combine with T1R3 to form heterodimeric sweet taste receptors. Indeed, rat T1R2 has been shown recently to function in combination with T1R3 to recognize a subset of sweet taste stimuli, a finding that has been proposed to reflect the involvement of additional combinations of T1Rs in sweet taste (6). In this study we cloned and functionally expressed human and rat T1Rs. Human and rat T1R2͞ T1R3 recognized all sweet taste stimuli tested, and human and rat T1R1͞T1R3 recognized umami taste stimuli. These findings suggest that different combinations of T1Rs function as heterodimeric sweet and umami taste receptors.Material and Methods T1R Cloning. Intronless human T1R expression constructs were generated in a pEAK10-derived vector (Edge Biosystems, Gaithersburg, MD) by a combination of cDNA-based and genomic DNA-based methods. To generate the full-length T1R1 expression construct, two 5Ј coding exons identified in a cloned T1R1 interval (GenBank accession no. AL159177) were combined by PCR overlap and then joined to a 5Ј-truncated testis cDNA clone. The T1R2 expression construct was generated from a partially sequenced T1R2 genomic interval. Two missing T1R2 5Ј introns were identified by screening shotgun libraries of the cloned genomic interval using probes derived from the corresponding rat coding sequence. Coding exons then were combined by PCR overlap to produce the full-length expression construct. The T1R3 e...

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Taste of glutamate salts in young and elderly subjects: Role of inosine 5′-monophosphate and ions

Cited by 51 publications

References 17 publications

Different functional roles of T1R subunits in the heteromeric taste receptors

Different functional roles of T1R subunits in the heteromeric taste receptors

A Possible Application of Monosodium Glutamate to Nutritional Care for Elderly People

Human receptors for sweet and umami taste

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