2009 Abstracts - Association for Chemoreception Sciences

G protein-coupled receptors for bitter, sweet and umamicompounds, and are the source of ATP secretion. These cells arebelieved to secrete ATP through gap junction hemichannels.Based on studies from isolated taste cells, we have postulated thatATP secreted from Receptor cells acts within the taste bud toexcite adjacent Presynaptic (Type III) cells (Huang et al2007). This however, remains to be established in more intactpreparations. Here we use lingual slices containing intact tastebuds to test the hypothesis in detail. We used confocal Ca 2+imaging to track taste stimulation of Receptor and Presynaptictaste cells. Incubating the tissue with an ecto-ATPase (apyrase,30 units/ml) reversibly blocked signal transfer from Receptorto Presynaptic cells, consistent with ATP being thetransmitter. Inhibiting pannexin 1 (Px1) gap junctionhemichannels with CO 2 -saturated buffer reduced cell-cellsignaling (N.B., intracellular acidification with CO 2 -buffer is apotent blocker of Px1 channels). Moreover, probenecid (1 mM),an antagonist of Px1 channels (Silverman et al 2008; Ma et al 2008)significantly reduced cell-cell signaling between Receptor andPresynaptic cells. These findings strongly support the hypothesisthat in situ, gustatory Receptor cells secrete ATP via Px1hemichannels when taste buds are stimulated and that thereleased ATP excites adjacent Presynaptic cells. These findingsare being used to develop a model for signal processing inmammalian taste buds.#P180 Poster session IV: Chemosensory transductionand perireceptor eventsTaste cells express and secrete glucagon-like peptide 1Zaza Kokrashvili, Robert F. MargolskeeMount Sinai School of Medicine New York, NY, USA#P181 Poster session IV: Chemosensory transductionand perireceptor eventsSodium/calcium exchangers selectively contribute to theregulation of cytosolic calcium levels in mouse taste cellsAgnieszka I. Laskowski, Kathryn F. MedlerUniversity at Buffalo Buffalo, NY, USAThe detection of gustatory stimuli depends on the activation ofdiverse signaling pathways that are selectively expressed in tastereceptor cells in the oral cavity. Some taste stimuli activateG-protein coupled receptors (GPCRs) that cause calcium releasefrom intracellular stores while other stimuli depolarize taste cellsto cause calcium influx through voltage-gated calcium channels(VGCCs). We have recently shown that activation of these twotypes of signaling pathways generate significantly differentcalcium responses within taste cells (Hacker et al., 2008) and wepredicted that the mechanisms needed to regulate these differentcalcium loads may also differ. To date, however, the calciumbuffering mechanisms in taste cells have not been well studied.We recently demonstrated that mitochondria make significantcontributions to the regulation of cytosolic calcium in taste cells(Hacker & Medler, 2008) but no other calcium bufferingmechanisms in taste cells have been identified. In this study, weused calcium imaging to characterize the role of sodium/calciumexchangers (NCXs) in regulating cytosolic calcium in tastecells. We found that NCXs make important contributions to themaintenance of resting calcium levels in taste cells and that theseproteins selectively contribute to the regulation of evoked calciumresponses. RT-PCR analysis revealed that multiple NCX andsodium/calcium/potassium exchangers (NCKX) are expressed intaste cells.P O S T E R SWe previously observed that gustducin, T1r receptors and severalother taste signaling elements are expressed in duodenalenteroendocrine L cells that express glucagon-like peptide 1(GLP-1). We determined that gustducin and T1r3 are critical toenteroendocrine L cell release of GLP-1 in response to glucose.A number of years ago we speculated that if the gut’s L cellsexpressed taste elements then taste cells might in turn expressGLP-1 and other L cell hormones. We have found that this isindeed the case and have examined the function of hormonesreleased from these “endocrine taste cells.” METHODS: RT-PCR, in situ hybridization and immunohistochemistry were usedto examine expression of GLP-1 and other gut hormones in tastecells. ELISA was used to monitor in vivo release of GLP-1 fromtaste cells into the bloodstream in response to glucose and othertastants. Esophagealectomy/vagotomy was done to eliminatedirect or indirect stimulation of enteroendocrine L cells in gut.Circumvallate papillae explants in culture were examined for theability to release GLP-1 after tastant stimulation. RESULTS:Taste cells were found to express GLP-1, glucagon, PYY andother gut hormones. Patterns of expression indicated thatgustducin-expressing type II cells and other subtypes of taste cellsexpress GLP-1. In wild-type mice, with or without vagotomy,application of glucose to the tongue induced a rapid elevation ofGLP-1 in the bloodstream. Stimulation of taste cell explants withglucose led to release of GLP-1 into the medium. Glucosestimulation of gustducin-null mice did not lead to significantrelease of GLP-1 from taste cells in vivo or in explants.CONCLUSIONS: The cephalic phase rise in circulatingGLP-1 depends on direct release of GLP-1 from gustducinexpressingtaste cells into the bloodstream.#P182 Poster session IV: Chemosensory transductionand perireceptor eventsThe multiple PDZ domain protein 1 (MUPP1) – Role in theolfactory signal transduction cascadeSabrina Baumgart, Ruth C. Dooley, Hanns Hatt, Eva M.NeuhausRuhr-University Bochum Bochum, GermanyThe complex network of the olfactory signal transductionpathway, found in olfactory sensory neurons (OSNs), enablesmammals to detect and discriminate between thousands ofdifferent odorants. Until now, the importance of organizing thevarious interaction partners of olfactory receptors (ORs) is notwell understood. For diverse cell signalling cascades interactionswith PDZ domain containing proteins, which assemble definedprotein networks and thereby regulate signalling events, arecharacterized. The Multiple PDZ Domain Protein 1, MUPP1,consists of 13 individual PDZ domains and interacts withdifferent GPCRs such as the serotonin receptor 5-HT 2c and theGABA B receptor. We demonstrate that this scaffolding protein ishighly expressed in the dendritic knobs and cilia of olfactorysensory neurons. We further found that ORs and MUPP1 interactin vitro and in the recombinant expression system. ThereforeMUPP1 represents a possible nucleator or regulator of theolfactory response by acting as first building block of a putative“olfactosome”. The physiological role of MUPP1 inchemosensory systems and the identification of unknowninteraction partners are currently investigated.Abstracts | 83