title: Functional expression of M3, a muscarinic acetylcholine receptor subtype, in taste bud cells of mouse fungiform papillae.
abstract: Taste bud cells (TBCs) express various neurotransmitter receptors assumed to facilitate or modify taste information processing within taste buds. We investigated the functional expression of muscarinic acetylcholine receptor (mAChR) subtypes, M1-M5, in mouse fungiform TBCs. ACh applied to the basolateral membrane of TBCs elevates the intracellular Ca(2+) level in a concentration-dependent manner with the 50% effective concentration (EC(50)) of 0.6 microM. The Ca(2+) responses occur in the absence of extracellular Ca(2+) and are inhibited by atropine, a selective antagonist against mAChRs. The order of 50% inhibitory concentration (IC(50)) examined with a series of antagonists selective to mAChR subtypes shows the expression of M3 on TBCs. Perforated whole-cell voltage clamp studies show that 1 microM ACh blocks an outwardly rectifying current and that 100 nM atropine reverses the block. Reverse transcriptase-mediated polymerase chain reaction studies suggest the expression of M3 but not the other mAChR subtypes. Immunohistochemical studies show that phospholipase Cbeta-immunoreactive TBCs and synaptosome-associated protein of 25 kDa-immunoreactive nerve endings are immunoreactive to a transporter that packs ACh molecules into synaptic vesicles (vesicular acetylcholine transporter). These results show that M3 occurs on a few fungiform TBCs and suggest that a few nerve endings, and probably a few TBCs, release ACh by exocytosis. The role of ACh in taste responses is discussed.
authors.affiliation: Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology, Hibikino 2-4, Kitakyushu, Japan.
authors.forename: Kohgaku
authors.initials: K
authors.lastname: Eguchi
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Ohtubo
authors.forename: Kiyonori
authors.initials: K
authors.lastname: Yoshii
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D003959:Diamines / Q000494:pharmacology; D004594:Electrophysiology; D015870:Gene Expression / Q000187:drug effects; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000032:analysis; D051379:Mice; D008815:Mice, Inbred Strains; D018727:Muscarinic Antagonists / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D054799:Phospholipase C beta / Q000032:analysis; D010880:Piperidines / Q000494:pharmacology; D010890:Pirenzepine / Q000494:pharmacology; D043587:Receptor, Muscarinic M3 / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000502:physiology; D011976:Receptors, Muscarinic / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050825:Synaptosomal-Associated Protein 25 / Q000032:analysis; D013650:Taste Buds / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014331:Tropicamide / Q000494:pharmacology; D050494:Vesicular Acetylcholine Transport Proteins / Q000032:analysis / Q000235:genetics
chemical_list: D003959:Diamines; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018727:Muscarinic Antagonists; D010880:Piperidines; D043587:Receptor, Muscarinic M3; D011976:Receptors, Muscarinic; C493460:Slc18a3 protein, mouse; C494209:Snap25 protein, mouse; D050825:Synaptosomal-Associated Protein 25; D050494:Vesicular Acetylcholine Transport Proteins; D010890:Pirenzepine; D001285:Atropine; C042375:4-diphenylacetoxy-1,1-dimethylpiperidinium; D054799:Phospholipase C beta; C518037:Plcb2 protein, mouse; D014331:Tropicamide; D000109:Acetylcholine; C054938:methoctramine