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edema of the tongue during acute exposure and looked similar to
control tissue in which only ethanol was applied. As a positive
control, capsaicin at 100 ppm in ethanol was applied and produced
widespread staining with Evans Blue, indicating edema. Results of
taste bud volumes from tongue tissue in animals given 5 ppm
capsaicin solution (e.g. a higher dose than earlier work) will be
also be presented.
#P237
POSTER SESSION VI:
OLFACTION CNS; TASTE PERIPHERY &
CNS; MULTIMODAL RECEPTION
Vertebrate Bitter Taste Receptors
Maik Behrens, Ulrike Reichelt, Wolfgang Meyerhof
German Institute of Human Nutrition Potsdam-Rehbruecke/
Molecular Genetics Nuthetal, Germany
Vertebrate bitter taste perception is facilitated by a variable number
of bitter taste receptor (
Tas2r
) genes. Whereas many vertebrate
species, including humans, possess average numbers of
Tas2r
genes, some species fall below or exceed this number by far. At the
extremes, species can have as few as 3 functional
Tas2r
genes, such
as chicken, and as many as ~50
Tas2r
genes in frogs. In humans,
the repertoire of Tas2rs consists of 3 broadly tuned receptors and
several receptors with a limited range of agonists in addition to
those receptors exhibiting an average breadth of tuning. To
elucidate whether extreme low or high numbers of functional
Tas2r
genes rather relate to the average tuning properties of the
corresponding receptors or whether they may reflect elevated or
reduced importance of bitter taste
per se
in different vertebrate
species, we performed functional calcium imaging experiments.
We cloned all 3 chicken (
G. gallus
) Tas2rs and 6 Tas2rs of the
African clawed frog covering major branches of the phylogenetic
tree of
X. tropicalis Tas2r
genes, and screened them with ~50 bitter
compounds. Whereas all chicken Tas2rs represent broadly tuned
receptors suggesting that a low number of
Tas2r
genes indicate
rather wide average agonist spectra, frog Tas2rs differed
considerably in their breadth of tuning, ranging from broad to
rather narrowly tuned ones. We conclude that a low number of
functional
Tas2r
genes can be compensated by an increased
average breadth of tuning and, hence, is not necessarily correlated
with a reduced importance of bitter taste for the corresponding
species. A high number of functional Tas2r genes, however, may
allow the generation of more specialized receptors perhaps
efficiently protecting a species against specific toxins in addition
to broadly tuned “generalist” receptors. Acknowledgements:
Supported by the German Research Foundation (DFG
(Me 1024/3-2) to WM).
#P238
POSTER SESSION VI:
OLFACTION CNS; TASTE PERIPHERY &
CNS; MULTIMODAL RECEPTION
Expression and Functional Characterization of Bitter Taste
Receptors in Mammalian Testis
Jiang Xu
1
, Feng Li
1
, Jie Cao
1
, Naoko Iguchi
1
, Dieter Riethmacher
2
,
Minliang Zhou
1
, Liquan Huang
1
1
Monell Chemical Senses Center Philadelphia, PA, USA,
2
University of Southampton, Faculty of Medicine, Human
Development and Health Southampton, United Kingdom
Mammalian spermatogenesis and sperm maturation are susceptible
to the effects of internal and external factors. However, how male
germ cells interact and respond to these elements including those
potentially toxic substances is poorly understood. Here we show
that many bitter taste receptors (T2rs), which are believed to
function as gatekeepers in the oral cavity to detect and innately
prevent the ingestion of poisonous bitter-tasting compounds, are
expressed in mouse seminiferous tubules. Our
in situ
hybridization
results indicate that Tas2r transcripts are expressed postmeiotically.
Transgenic studies with mouse lines generated using the promoter
of the mouse bitter taste receptor gene
Tas2r105
confirmed their
expression in the haploid germ cells. Furthermore, the expression
of a toxin protein, diphtheria toxin A (DTA), driven by the
Tas2r105 promoter, led to the ablation of nearly all spermatozoa,
indicating that many but not all spermatogenic cells expressed
Tas2r105. Functional analysis showed that wild-type spermatids
and spermatozoa responded to both naturally occurring and
synthetic bitter-tasting compounds by increasing intracellular free
calcium concentrations. In congruency with the Tas2R105
expression pattern, the majority of spermatids and sperm cells were
responsive to this receptor’s agonist cycloheximide. Nevertheless,
individual male germ cells exhibited different ligand-activation
profiles, indicating that each cell may express a unique subset of
T2r receptors. Taken together, our data strongly suggest that male
germ cells, like taste bud cells in the oral cavity and solitary
chemosensory cells in the airway, utilize T2r receptors to sense
chemicals in the milieu and that the outcome may affect
spermatogenesis and fertilization.
#P239
POSTER SESSION VI:
OLFACTION CNS; TASTE PERIPHERY &
CNS; MULTIMODAL RECEPTION
Molecular Mechanism for the Sweet Taste Enhancer Selectivity
Feng Zhang, Fernando Echeverri, Yi Ren, Catherine Tachdjian,
David L. Linemeyer
Senomyx, Inc. San Diego, CA, USA
Sweet taste enhancers have been developed at Senomyx to reduce
dietary sugar intake for human health benefits. Sucralose enhancer
SE-2
and sucrose enhancer
SE-3
have been used as tool molecules
to understand the mechanism of these positive allosteric modulators
(PAMs) for the sweet taste receptor, which may also apply to other
family C GPCRs. Our mutagenesis studies of the human sweet taste
receptor have identified a group of shared residues in the T1R2
VFT domain that are required for the enhancement activity of both
PAMs. However, the molecular mechanism for the selective effect
of these small molecules on sucralose and sucrose remains unclear.
Here for the first time, we have identified new key residues in the
T1R2 VFT domain required for the selectivity of these PAMs.
SE-2 and SE-4
(a more potent sucrose enhancer) require different
sets of pincer residues for their selective enhancement effects on
sucralose and sucrose. The differential binding mode of these small
106 | AChemS Abstracts 2012
Abstracts are printed as submitted by the author(s)
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