Comprehensive Study on G protein alpha-Subunits in Taste Bud Cells, with Special Reference to the Occurrence of Galphai2 as a Major Galpha Species

Kusakabe, Yuko; Yasuoka, Akihito; Asano-Miyoshi, Misaki; Iwabuchi, Kyoko; Matsumoto, Ichiro; Arai, Soichi; Emori, Yasufumi; Abe, Keiko

doi:10.1093/chemse/25.5.525

Cited by 67 publications

(51 citation statements)

References 32 publications

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“…The G␤␥ arm stimulates PLC␤ 2 and results in calcium elevation. The G␣ arm may trigger cAMP modulation via the action of G␣ s , G␣ i , or G␣ gustducin , each of which is expressed in taste buds (20,23,25). Specifically, G␣ s , a subunit that stimulates all ACs, may give rise to increases of cAMP (for sucrose).…”

Section: Discussionmentioning

confidence: 99%

Tastants evoke cAMP signal in taste buds that is independent of calcium signaling

Trubey¹,

Culpepper²,

Maruyama

et al. 2006

American Journal of Physiology-Cell Physiology

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We previously showed that rat taste buds express several adenylyl cyclases (ACs) of which only AC8 is known to be stimulated by Ca 2ϩ . Here we demonstrate by direct measurements of cAMP levels that AC activity in taste buds is stimulated by treatments that elevate intracellular Ca 2ϩ . Specifically, 5 M thapsigargin or 3 M A-23187 (calcium ionophore), both of which increase intracellular Ca 2ϩ concentration ([Ca 2ϩ ]i), lead to a significant elevation of cAMP levels. This calcium stimulation of AC activity requires extracellular Ca 2ϩ , suggesting that it is dependent on Ca 2ϩ entry rather than release from stores. With immunofluorescence microscopy, we show that the calcium-stimulated AC8 is principally expressed in taste cells that also express phospholipase C␤2 (i.e., cells that elevate [Ca 2ϩ ]i in response to sweet, bitter, or umami stimuli). Taste transduction for sucrose is known to result in an elevation of both cAMP and calcium in taste buds. Thus we tested whether the cAMP increase in response to sucrose is a downstream consequence of calcium elevation. Even under conditions of depletion of stored and extracellular calcium, the cAMP response to sucrose stimulation persists in taste cells. The cAMP signal in response to monosodium glutamate stimulation is similarly unperturbed by calcium depletion. Our results suggest that tastant-evoked cAMP signals are not simply a secondary consequence of calcium modulation. Instead, cAMP and released Ca 2ϩ may represent independent second messenger signals downstream of taste receptors.calcium-sensitive adenylyl cyclase; capacitative entry; cross talk; taste transduction DURING THE PAST DECADE, numerous advances have been made in our understanding of taste transduction mechanisms. Most tastants of the sweet, bitter, and umami classes are thought to activate G protein-coupled taste receptors and their heterotrimeric G proteins. The G␥ 13 subunit appears to be taste specific and associated with G␤ 1 (14). This G␤ 1 ␥ 13 dimer has been shown directly to activate a phospholipase C (PLC␤ 2 ), stimulating the production of inositol 1,4,5-trisphosphate (IP 3 ) and eventually triggering an increase in cytoplasmic Ca 2ϩ (14,23,35,38). Strong support for this sequence of signaling events is derived from the pronounced taste deficit that results from genetic ablation of PLC␤ 2 (45). Although release of stored Ca 2ϩ (triggered by PLC␤ 2 activity) is essential, taste-evoked calcium transients in taste cells may also include a component of capacitative entry from the extracellular medium (28). Despite the recent emphasis on this IP 3 -mediated calcium release pathway, there is evidence that changes in cAMP and cGMP concentration occur after tastant stimulation. Cyclic nucleotide modulation has been demonstrated after stimulation with some sweet, bitter, and umami stimuli (1,39,44), and exogenously applied cAMP appears to mimic tastant-evoked activity (8). Nevertheless, the significance and source of cAMP and cGMP in taste transduction are unclear, given the essential role of...

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Section: Discussionmentioning

confidence: 99%

Tastants evoke cAMP signal in taste buds that is independent of calcium signaling

Trubey¹,

Culpepper²,

Maruyama

et al. 2006

American Journal of Physiology-Cell Physiology

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“…Not surprisingly, receptors sensing sour and salty tastes are ion channels. On the other hand, bitter, sweet, and umami receptors are GPCRs and couple to gustducin, a G-protein specifically involved in taste processing (Chandrashekar et al, 2000), but also to other G-proteins (Kusakabe et al, 2000;Ozeck et al, 2004). Taste receptors for bitter, sweet, and umami are localized in type II cells, which are part of the taste buds on the surface of the tongue.…”

Section: A Taste-more Than Just a Pleasurementioning

confidence: 99%

Allosteric Modulation of Family C G-Protein-Coupled Receptors: from Molecular Insights to Therapeutic Perspectives

2011

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“…One major transduction pathway for umami taste, which is common to sweet and bitter tastes, has been proposed. That is, binding of umami compounds preferentially to T1R1/T1R3 receptors activates the heterodimeric G proteins α-gustducin 36) or Gαi, 48) leading to the release of the Gβγ subunits and the subsequent stimulation of PLCβ2. 49) Activation of PLCβ2 hydrolyses phosphatidylinositol-4,5-bisphosphate to produce the second messengers IP 3 and diacylglycerol.…”

Section: Receptors and Transduction Pathways For Umami Tastementioning

confidence: 99%

Multiple Umami Receptors and Their Variants in Human and Mice

Jyotaki

Shigemura

Ninomiya

2009

JOURNAL OF HEALTH SCIENCE

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L-Glutamate and 5 -ribonucleotides are known to elicit a unique taste, "umami," that is distinct from the tastes of sweet, salt, sour and bitter. Recent progress in molecular biology has identified several umami receptor candidates, such as the heterodimer T1R1/T1R3, and brain-expressed and taste-expressed type 1 and 4 metabotropic glutamate receptors (brain-and taste-mGluR1 and mGluR4). This paper summarizes recent findings on the receptor system for umami taste. Most of the findings support the idea that multiple receptors exist for umami taste, at least in mice. The accumulating evidence indicates that the potential role of the signal mediated by the transduction pathway involving T1R1/T1R3 may be different from that mediated by the pathway involving mGluRs. The former signal occurs mainly in the anterior tongue, and plays a major role in preference behavior, whereas the latter occurs mainly in the posterior tongue, is active in mice lacking T1R3, Gα-gustducin, IP 3 R3 or TRPM5, and contributes to behavioral discrimination between umami and other taste compounds. In humans, unlike in mice, T1R1/T1R3 acts as an umami-specific receptor that can discriminate between umami and other tastes, and thus account for umami-linked preferences or discrimination.

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Comprehensive Study on G protein alpha-Subunits in Taste Bud Cells, with Special Reference to the Occurrence of Galphai2 as a Major Galpha Species

Cited by 67 publications

References 32 publications

Tastants evoke cAMP signal in taste buds that is independent of calcium signaling

Tastants evoke cAMP signal in taste buds that is independent of calcium signaling

Allosteric Modulation of Family C G-Protein-Coupled Receptors: from Molecular Insights to Therapeutic Perspectives

Multiple Umami Receptors and Their Variants in Human and Mice

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