2009 Abstracts - Association for Chemoreception Sciences

#P192 Poster session IV: Chemosensory transductionand perireceptor eventsAcidic substances added in the oral cavity reduce ourbitter taste sensation by pH-dependent inhibition ofhTAS2R responseTakanobu Sakurai 1,2 , Takumi Misaka 2 , Toshitada Nagai 2 , YoshiroIshimaru 2 , Shinji Matsuo 1 , Tomiko Asakura 2 , Keiko Abe 21General Research Institute of Food Science and Technology,Nissin Foods Holdings Co., Ltd. Shiga, Japan, 2 Department ofApplied Biological Chemistry, Graduate School of Agriculturaland Life Sciences, The University of Tokyo Tokyo, JapanSome acidic peptides are known to reduce our bitter tastesensation, although the mechanism remains to be elucidated.The recent progress in taste molecular biology has revealed thatG protein-coupled receptor members of the TAS2R family actto receive bitter tastants; 25 members have been identifiedas bitter taste receptors including hTAS2R16 that responds tob-glucopyranosides. We investigated the bitterness-maskingeffects of acidic dipeptides by calcium imaging analysis usingHEK293T cells that transiently expressed hTAS2R16 along withG 16gust44. Salicin, a cognate bitter tasting ligand, was used in thepresence or absence of acidic dipeptides, with the result that acidicdipeptides significantly reduced the receptor response to thisligand. Interestingly, a variety of acidic substances includingamino, organic and inorganic acids as well inhibited the responseof hTAS2R16 to salicin, while no such effect was observed withneutral peptides and amino acid, and as well as acidic amino acidsalts. The inhibition took place depending on the pH values as aresult of the addition of acids but not on their concentrations.We also confirmed the inhibition of hTAS2R38 response toN-phenylthiourea and 6-propyl-2-thiouracil at low pH. Ourresults suggest that the reduction of our bitter taste sensation byacidic dipeptides in particular and sour taste substances in generalcan be attributed to their inhibitory effects on hTASA2Rmolecules and also that the receptor-environmental pH in theoral cavity is a critical factor responsible for this sensory event.Supported by Research and Development Program forNew Bio-industry Initiatives.#P193 Poster session IV: Chemosensory transductionand perireceptor eventsUnraveling the Signal Transduction Cascade Mediated by theOlfactory Receptor hOR51E2 in Prostate Cancer CellsJennifer Spehr, Markus Osterloh, Weiyi Zhang, Lian Gelis, HannsHatt, Eva M. NeuhausDept. of Cellular Physiology, Ruhr-University Bochum Bochum,GermanyOlfactory receptors (ORs) are expressed not only in the sensoryneurons of the olfactory epithelium but also in various othertissues. The functions of ORs in these tissues are largelyunknown. We previously reported that the human OR51E2,which is endogenously overexpressed in prostate cancer cells, canbe activated by androstenone derivates as well as the odorantionone. We could also show that exposure to ionone resulted ininhibition of cell proliferation as well as induction of apoptosis.Here, we characterized the signal transduction mechanisminduced by activation of OR51E2 in LNCaP cells (prostate cancercell line) using a combination of calcium imaging, patch clamp andbiochemical techniques. Ionone stimulation leads to an increase ofintracellular calcium, which at least in part depends onextracellular calcium. Electrophysiological measurements revealedan ionone dependent opening of a calcium conductance in theplasma membrane. Further biophysical and pharmacologicalanalysis identified TRPV6 as transduction channels, a finding thatwas confirmed by RNAi experiments. The expression of TRPV6in prostate cancer cells has been described before but the functionas well as the activation mechanism was still elusive. Currently, weinvestigate how activation of the OR51E2 leads to an opening ofTRPV6 channels. In summary we report the first endogenouslyexpressed OR that couples to a signal transduction cascadedifferent from the one used in olfactory sensory neurons. Namelywe show that OR activation leads to an opening of TRPV6channels.#P194 Poster session IV: Chemosensory transductionand perireceptor eventsExpression and Functionality of Oxytocin Receptor inMouse Taste CellsMichael Sinclair 1 , Gennady Dvoryanchikov 2 , KatsuhikoNishimori 3 , Nirupa Chaudhari 1,21Program in Neurosciences, University of Miami Miller School ofMedicine Miami, FL, USA, 2 Department of Physiology andBiophysics, University of Miami Miller School of Medicine Miami,FL, USA, 3 Department of Molecular and Cell Biology, GraduateSchool of Agricultural Science,Tohoku University Miyagi 981-8555, JapanOxytocin (Oxt), in addition to its effects on reproduction andcertain behaviors, may also influence taste and feeding. Forexample, Oxt -/- mice overconsume sweet solutions regardless ofcaloric content. And mice lacking the cognate receptor, i.e. Oxtr -/- ,are obese. We asked if Oxtr is expressed and functional in mousetaste buds. Using RT-PCR, we detected Oxtr mRNA in vallate,foliate, palatal and fungiform taste buds. In vallate taste buds,Oxtr mRNA is 1000-fold less abundant than b-actin mRNA.Immunocytochemistry revealed that Oxtr is expressed in cells thatare neither Type II/Receptor cells nor GAD-expressing TypeIII/Presynaptic cells. In taste buds from Oxtr-YFP(Venus) knockinmice also, we found that YFP-labeled (that is, Oxtr-expressing)taste cells did not overlap with PLC 2 immunofluorescence. Thus,Oxtr expression might be limited to Type I taste cells. RT-PCR onisolated single taste cells confirmed that Oxtr is expressed only inType I/glial-like (NTPDase2-expressing) cells. Using Fura-2 Ca 2+imaging, we observed dose-dependent increases of intracellular[Ca 2+ ] in vallate taste cells and this was attributed to release fromstores. Responses were detectable at 10 nM Oxt, saturated at1mM, and displayed an EC 50 of ~30 nM, similar to the sensitivityof uterine smooth muscle, a known target of Oxt. The Oxtrantagonist, L-371,257, significantly decreased the Ca 2+ response.None of the isolated cells that responded to Oxt expressedPLCb2. In sum, our data indicate that Oxtr is expressed in asubset of taste cells that are likely Type I/glial-like, and that thesecells can respond to physiological concentrations of Oxt via Oxtr.Therefore, it is possible that Oxt may exert at least some of itseffects on taste and feeding at the level of the taste bud.P O S T E R SAbstracts | 87