Transduction of bitter and sweet taste by gustducin

@article{Wong1996TransductionOB,
  title={Transduction of bitter and sweet taste by gustducin},
  author={Gwendolyn T. Wong and Kimberley S. Gannon and Robert F. Margolskee},
  journal={Nature},
  year={1996},
  volume={381},
  pages={796-800}
}
SEVERAL lines of evidence suggest that both sweet and bitter tastes are transduced via receptors coupled to heterotrimeric guanine-nucleotide-binding proteins (G proteins) (reviewed in refs 1, 2). Gustducin is a taste receptor cell (TRC)-specific G protein that is closely related to the transducins3. Gustducin and rod transducin, which is also expressed in TRCs (ref. 4), have been proposed to couple bitter-responsive receptors to TRC-specific phosphodiesterases to regulate intracellular cyclic… 
Characterization and solubilization of bitter-responsive receptors that couple to gustducin.
TLDR
It is shown that gustducin is expressed in bovine taste tissue and that both gust Ducin and transducin, in the presence of bovines taste membranes, can be activated specifically by several bitter compounds, including denatonium, quinine, and strychnine.
Gustducin and its Role in Taste
TLDR
A proposed mechanism for α-gustducin involves coupling specific cell-surface receptors with a cyclic nucleotide phosphodiesterase which would open a cyclIC nucleotide-suppressible cation channel leading to influx of calcium, and ultimately leading to release of neurotransmitter.
Blocking taste receptor activation of gustducin inhibits gustatory responses to bitter compounds.
TLDR
AMP and certain related compounds may bind to bitter-responsive taste receptors or interfere with receptor-G protein coupling to serve as naturally occurring taste modifiers.
Umami Taste Responses Are Mediated by α-Transducin and α-Gustducin
TLDR
It is found that αt-rod played no role in taste responses to the salty, bitter, and sweet compounds tested or to IMP but was involved in the umami taste of MSG and MPG.
Role of the G-Protein Subunit α-Gustducin in Taste Cell Responses to Bitter Stimuli
TLDR
It is found that the G-protein α subunit Gαi2 is present in most bitter-responsive cells and thus may also play a role in bitter taste transduction and thus appears to be the consequence of a reduced number of bitter-activated taste cells, as well as reduced sensitivity.
A Plethora of Taste Receptors
Dominant loss of responsiveness to sweet and bitter compounds caused by a single mutation in α-gustducin
TLDR
Generating a dominant-negative form of α-gustducin and expressing it as a transgene from the α-magnifying lens suggests that other guanine nucleotide-binding regulatory proteins expressed in theα-gUSTducin lineage of taste cells mediate responses to bitter and sweet compounds.
Gγ13 colocalizes with gustducin in taste receptor cells and mediates IP3 responses to bitter denatonium
TLDR
It is concluded that gustducin heterotrimers transduce responses to bitter and sweet compounds via α-gustducin's regulation of phosphodiesterase (PDE) and Gβγ's activation of phospholipase C (PLC).
Partial Rescue of Taste Responses of α-Gustducin Null Mice by Transgenic Expression of α-Transducin
TLDR
It is suggested that alpha-transducin and alpha-gustducin may differ, at least in part, in their function in these cells, although this conclusion must be qualified because of the limited fidelity of the transgene expression.
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References

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TLDR
It is suggested that rod transducin tranduces bitter taste by coupling taste receptor(s) to taste-cell phosphodiesterase through the recently identified cyclic-nucleotide-suppressible conductance.
A cyclic–nucleotide–suppressible conductance activated by transducin in taste cells
TLDR
It is proposed that transducin, via phosphodiesterase, decreases cyclic nucleotide levels to activate the cyclic-nucleotide-suppressible conductance, leading to Ca2+ influx and taste-cell depolarization.
Rapid kinetics of second messenger production in bitter taste.
TLDR
The rapid kinetics, transient nature, and specificity of the bitter taste stimulus-induced IP3 formation are consistent with the role of IP3 as a second messenger in the chemoelectrical transduction of bitter taste.
Chemosensory transduction mechanisms in taste.
Taste receptor cells transduce sweet, sour, salty, and bitter chemicals into receptor potentials that ultimately result in the perception of taste. The mechanisms involved in this process are only
Gustducin is a taste-cell-specific G protein closely related to the transducins
A novel G protein α-subunit (α-gustducin) has been identified and cloned from taste tissue, α-Gustducin messenger RNA is expressed in taste buds of all taste papillae (circumvallate, foliate and
Transduction in taste receptor cells requires cAMP-dependent protein kinase
TLDR
It is shown that cAMP causes a substantial depolarization in these cells, which differs from that of olfactory3 and photoreceptor cells4,5, where cyclic nucleotides control unspecific channels by binding to them rather than by inducing their phosphorylation.
Cyclic nucleotides may mediate taste transduction
TLDR
The results suggest that a cyclic nucleotide enzymatic cascade, modulated by calcium ions, may mediate the potassium permeability that controls taste, in a way analogous to visual and olfactory transduction.
Sweet tastants stimulate adenylate cyclase coupled to GTP-binding protein in rat tongue membranes.
TLDR
Sucrose and other saccharides, which produce an appealing taste in rats, were found to significantly stimulate the activity of adenylate cyclase in membranes derived from the anterior-dorsal region of rat tongue, consistent with a sweet-taste transduction mechanism involving specific receptors, a guanine-nucleotide-binding protein and the cyclic AMP-generating enzyme.
A bitter substance induces a rise in intracellular calcium in a subpopulation of rat taste cells.
TLDR
The transduction of bitter taste may occur via a receptor-second messenger mechanism leading to neurotransmitter release and may not involve depolarization-mediated calcium entry.
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