2009 Abstracts - Association for Chemoreception Sciences

#P160 Poster session IV: Chemosensory transductionand perireceptor eventsPI3K-gamma in olfactory signal transduction in miceDaniela Brunert 1 , Kirill Y. Ukhanov 1 , Elizabeth A. Corey 1 ,Barry W. Ache 1,21Whitney Laboratory, Center for Smell and Taste, McKnight BrainInstitute, University of Florida Gainesville, FL, USA, 2 Depts. ofZoology and Neuroscience, University of Florida, Gainesville, FL,USAresponses to glutamate were measured in the presence and absenceof CNQX, an ionotropic AMPA/kainate glutamate receptorantagonist. CNQX partially blocked the responses to MSG inType III cells, suggesting that AMPA/kainate receptors arefunctionally expressed in these taste cells. Hence, both Type IIand Type III cells respond to MSG, but with different sensitivity.Further, responses to low concentrations appear to be at leastpartially mediated by AMPA/kainate receptors. This work wassupported by NIH grant DC00766 and a 3ARP grant fromAjinomoto.P O S T E R SRecent findings in rat olfactory receptor neurons (ORNs) suggestphosphoinositide 3-kinase (PI3K) -dependent signalling may playa role in mammalian olfactory signal transduction. In order tobring the power of genetically modified rodents to this questionwe tested whether PI3K has a similar effect on the output ofmouse ORNs. We show that the pan specific PI3K inhibitorWortmannin increases the calcium response of acutely dissociatedmouse ORNs to a complex odorant mixture (Henkel 100) inapproximately the same percentage of cells as with rat ORNs.The catalytic subunits of the alpha, beta and gamma isoforms ofPI3K are expressed in the mouse olfactory epithelium (OE) andcan be localized to the ORNs. As with rat ORNs, isoformspecificblockade of the beta (TGX-221) and gamma (AS252424)isoforms of PI3K implicate both isoforms in modulating odorantdependentsignalling. These results suggest that the PI3Kdependent modulation of olfactory signal transduction originallycharacterized in rats generalizes to mice. Mice deficient inPI3K-beta are embryonically lethal, but mice deficient inPI3K-gamma are viable and do not show obvious differences inOE morphology and retain cyclic nucleotide-dependentresponsiveness to odorants. These mice are being used to examinethe specific role and mechanism of PI3K-gamma in olfactorysignal transduction.#P161 Poster session IV: Chemosensory transductionand perireceptor eventsDifferential sensitivity to monosodium glutamate inType II and Type III taste cellsAurelie Vandenbeuch 1,2 , Catherine B. Anderson 1,2 ,Sue C. Kinnamon 1,21University of Colorado Denver and Health Sciences CenterDenver, CO, USA, 2 Rocky Mountain Taste and Smell CenterDenver, CO, USAGlutamate receptors are expressed in taste cells and allow thedetection of umami taste stimuli via the G protein coupledreceptor T1R1-T1R3. Glutamate receptors may also be involvedin neurotransmission between nerve fibers and taste cells, orbetween different taste cell types. The aim of the present studywas to compare the physiological response to monosodiumglutamate (MSG) in identified types of taste cells. We isolatedtaste cells from circumvallate papillae and used calcium imaging tocharacterize MSG responses. We used T1R3-GFP mice to identifya subset of Type II taste cells, presumably those that express theumami taste receptor T1R1-T1R3. We used stimulation with highK + to identify Type III cells, as these are the only cells in the tastebud that possess voltage-gated Ca 2+ channels. T1R3-GFP tastecells failed to respond to MSG at concentrations below 10 mM.On the contrary, in Type III cells, responses to MSG wereobtained at 100µM. To determine whether these responses to lowconcentration of glutamate are mediated by ionotropic receptors,#P162 Poster session IV: Chemosensory transductionand perireceptor eventsThe Second Messenger Pathways in TRPC2 KnockoutMouse Vomeronasal Sensory NeuronsChun Yang 1 , Peng Zhang 2 , Rona J Delay 11Department of Biology, Vermont Chemical Sensory group,University of Vermont Burlington, VT, USA, 2 MassachusettsGeneral Hospital and Harvard Medical School Charlestown,MA, USAIn vomeronasal sensory neurons (VSNs), transient receptorpotential cation channels (TRPC2) play a large role in responsesto pheromones and odorants. TRPC2-/- mice fail to display themale-male aggressive behavior and mate indiscriminately (Stowerset al., 2002). However, pregnancy block, which requires afunctional vomeronasal organ (VNO), does occur in TRPC2-/-mice (Kelliher et al., 2006). This suggests the presence of aTRPC2-independent pathway in VSNs. To reveal the mechanismfor pheromone/odorant detection of VSNs, we investigated urineresponse in VSNs from wild-type and TRPC2-/- mice. Usingperforated patch clamp technique, we recorded responses to diluteurine in wild-type & TRPC2-/- VSNs. These urine responses inboth types appeared to be through the phospholipase C (PLC)pathway since they were completely blocked by the PLCinhibitor, U73122, although the response amplitude of TRPC2-/-VSNs was smaller than that for wild type. We asked which secondmessenger pathway mediates urine responses in knockout mice.Activation of the PLC pathway produces diacylglycerol (DAG),which directly gated TRPC2 chanels. However, DAG alsoproduces arachidonic acid (AA) via DAG lipase. Thus, we testedif a DAG lipase inhibitor, RHC80267, altered urine responses.We found that RHC80267 blocked urine-induced inward currentby ~60% in wild type VSNs while it abolished the urineresponses in TRPC2-/-. Moreover, AA itself induced an inwardcurrent in both wild type and knockout VSNs that was dependenton extracellular calcium. Using inside-out patches, we recordedCa2+-activated and AA-activated channel activity with aconductance of ~26 pS. Thus, our data suggested that in mouseVSNs, the pheromone/odor detection is carried out by bothDAG-TRPC2 and Ca2+/AA-cation channels pathways.Abstracts | 77