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Role of the ectonucleotidase NTPDase2 in taste bud function.

ABSTRACT: Taste buds are unusual in requiring ATP as a transmitter to activate sensory nerve fibers. In response to taste stimuli, taste cells release ATP, activating purinergic receptors containing the P2X2 and P2X3 subunits on taste nerves. In turn, the released ATP is hydrolyzed to ADP by a plasma membrane nucleoside triphosphate previously identified as nucleoside triphosphate diphosphohydrolase-2 (NTPDase2). In this paper we investigate the role of this ectonucleotidase in the function of taste buds by examining gene-targeted Entpd2-null mice globally lacking NTPDase2. RT-PCR confirmed the absence of NTPDase2, and ATPase enzyme histochemistry reveals no reaction product in taste buds of knockout mice, suggesting that NTPDase2 is the dominant form in taste buds. RT-PCR and immunocytochemistry demonstrated that in knockout mice all cell types are present in taste buds, even those cells normally expressing NTPDase2. In addition, the overall number and size of taste buds are normal in Entpd2-null mice. Luciferin/luciferase assays of circumvallate tissue of knockout mice detected elevated levels of extracellular ATP. Electrophysiological recordings from two taste nerves, the chorda tympani and glossopharyngeal, revealed depressed responses to all taste stimuli in Entpd2-null mice. Responses were more depressed in the glossopharyngeal nerve than in the chorda tympani nerve and involved all taste qualities; responses in the chorda tympani were more depressed to sweet and umami stimuli than to other qualities. We suggest that the excessive levels of extracellular ATP in the Entpd2-knockout animals desensitize the P2X receptors associated with nerve fibers, thereby depressing taste responses.

SUBMITTER: Vandenbeuch A

PROVIDER: S-EPMC3767538 | biostudies-literature | 2013 Sep

REPOSITORIES: biostudies-literature

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Role of the ectonucleotidase NTPDase2 in taste bud function.

Vandenbeuch Aurelie A Anderson Catherine B CB Parnes Jason J Enjyoji Keiichi K Robson Simon C SC Finger Thomas E TE Kinnamon Sue C SC

Proceedings of the National Academy of Sciences of the United States of America 20130819 36

Taste buds are unusual in requiring ATP as a transmitter to activate sensory nerve fibers. In response to taste stimuli, taste cells release ATP, activating purinergic receptors containing the P2X2 and P2X3 subunits on taste nerves. In turn, the released ATP is hydrolyzed to ADP by a plasma membrane nucleoside triphosphate previously identified as nucleoside triphosphate diphosphohydrolase-2 (NTPDase2). In this paper we investigate the role of this ectonucleotidase in the function of taste buds ...[more]

PMID: 23959882

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Project description:Key pointsTaste transduction occurs in taste buds in the tongue epithelium. The Ca2+ -activated Cl- channels TMEM16A and TMEM16B play relevant physiological roles in several sensory systems. Here, we report that TMEM16A, but not TMEM16B, is expressed in the apical part of taste buds. Large Ca2+ -activated Cl- currents blocked by Ani-9, a selective inhibitor of TMEM16A, are measured in type I taste cells but not in type II or III taste cells. ATP indirectly activates Ca2+ -activated Cl- currents in type I cells through TMEM16A channels. These results indicate that TMEM16A is functional in type I taste cells and contribute to understanding the largely unknown physiological roles of these cells.AbstractThe Ca2+ -activated Cl- channels TMEM16A and TMEM16B have relevant roles in many physiological processes including neuronal excitability and regulation of Cl- homeostasis. Here, we examined the presence of Ca2+ -activated Cl- channels in taste cells of mouse vallate papillae by using immunohistochemistry and electrophysiological recordings. By using immunohistochemistry we showed that only TMEM16A, and not TMEM16B, was expressed in taste bud cells where it largely co-localized with the inwardly rectifying K+ channel KNCJ1 in the apical part of type I cells. By using whole-cell patch-clamp recordings in isolated cells from taste buds, we measured an average current of -1083 pA at -100 mV in 1.5 μm Ca2+ and symmetrical Cl- in type I cells. Ion substitution experiments and blockage by Ani-9, a specific TMEM16A channel blocker, indicated that Ca2+ activated anionic currents through TMEM16A channels. We did not detect any Ca2+ -activated Cl- currents in type II or III taste cells. ATP is released by type II cells in response to various tastants and reaches type I cells where it is hydrolysed by ecto-ATPases. Type I cells also express P2Y purinergic receptors and stimulation of type I cells with extracellular ATP produced large Ca2+ -activated Cl- currents blocked by Ani-9, indicating a possible role of TMEM16A in ATP-mediated signalling. These results provide a definitive demonstration that TMEM16A-mediated currents are functional in type I taste cells and provide a foundation for future studies investigating physiological roles for these often-neglected taste cells.

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Role of the ectonucleotidase NTPDase2 in taste bud function.

Publications

Role of the ectonucleotidase NTPDase2 in taste bud function.

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