title: Expression of taste receptors in solitary chemosensory cells of rodent airways.
abstract: BACKGROUND
  Chemical irritation of airway mucosa elicits a variety of reflex responses such as coughing, apnea, and laryngeal closure. Inhaled irritants can activate either chemosensitive free nerve endings, laryngeal taste buds or solitary chemosensory cells (SCCs). The SCC population lies in the nasal respiratory epithelium, vomeronasal organ, and larynx, as well as deeper in the airway. The objective of this study is to map the distribution of SCCs within the airways and to determine the elements of the chemosensory transduction cascade expressed in these SCCs.
  
  
  METHODS
  We utilized a combination of immunohistochemistry and molecular techniques (rtPCR and in situ hybridization) on rats and transgenic mice where the Tas1R3 or TRPM5 promoter drives expression of green fluorescent protein (GFP).
  
  
  RESULTS
  Epithelial SCCs specialized for chemoreception are distributed throughout much of the respiratory tree of rodents. These cells express elements of the taste transduction cascade, including Tas1R and Tas2R receptor molecules, α-gustducin, PLCβ2 and TrpM5. The Tas2R bitter taste receptors are present throughout the entire respiratory tract. In contrast, the Tas1R sweet/umami taste receptors are expressed by numerous SCCs in the nasal cavity, but decrease in prevalence in the trachea, and are absent in the lower airways.
  
  
  CONCLUSIONS
  Elements of the taste transduction cascade including taste receptors are expressed by SCCs distributed throughout the airways. In the nasal cavity, SCCs, expressing Tas1R and Tas2R taste receptors, mediate detection of irritants and foreign substances which trigger trigeminally-mediated protective airway reflexes. Lower in the respiratory tract, similar chemosensory cells are not related to the trigeminal nerve but may still trigger local epithelial responses to irritants. In total, SCCs should be considered chemoreceptor cells that help in preventing damage to the respiratory tract caused by inhaled irritants and pathogens.
authors.affiliation: Rocky Mountain Taste and Smell Center, Department of Cell and Developmental Biology, University of Colorado at Denver & Health Sciences Center, Aurora, CO, USA. marco.tizzano@ucdenver.edu
authors.forename: Marco
authors.initials: M
authors.lastname: Tizzano
authors.forename: Mirko
authors.initials: M
authors.lastname: Cristofoletti
authors.forename: Andrea
authors.initials: A
authors.lastname: Sbarbati
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Finger
mesh_terms: D000818:Animals; D002628:Chemoreceptor Cells / Q000378:metabolism*; D005453:Fluorescence; D005455:Fluorescent Antibody Technique; D015870:Gene Expression; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D017403:In Situ Hybridization; D051379:Mice; D008822:Mice, Transgenic; D054799:Phospholipase C beta / Q000378:metabolism; D051381:Rats; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000166:cytology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D050053:TRPM Cation Channels / Q000378:metabolism; D013649:Taste / Q000502:physiology*; D015293:Transducin / Q000235:genetics / Q000378:metabolism; D014276:Trigeminal Nerve / Q000502:physiology; D000098706:Taste Receptors, Type 2
chemical_list: D043562:Receptors, G-Protein-Coupled; D050053:TRPM Cation Channels; C498617:Trpm5 protein, mouse; C431926:taste receptors, type 1; D000098706:Taste Receptors, Type 2; D049452:Green Fluorescent Proteins; C075192:gustducin; D054799:Phospholipase C beta; D015293:Transducin