title: Bitter tasting compounds dilate airways by inhibiting airway smooth muscle calcium oscillations and calcium sensitivity.
abstract: OBJECTIVE
  While selective, bitter tasting, TAS2R agonists can relax agonist-contracted airway smooth muscle (ASM), their mechanism of action is unclear. However, ASM contraction is regulated by Ca²⁺ signalling and Ca²⁺ sensitivity. We have therefore investigated how the TAS2R10 agonists chloroquine, quinine and denotonium regulate contractile agonist-induced Ca²⁺ signalling and sensitivity.
  
  
  METHODS
  Airways in mouse lung slices were contracted with either methacholine (MCh) or 5HT and bronchodilation assessed using phase-contrast microscopy. Ca²⁺ signalling was measured with 2-photon fluorescence microscopy of ASM cells loaded with Oregon Green, a Ca²⁺-sensitive indicator (with or without caged-IP₃). Effects on Ca²⁺ sensitivity were assessed on lung slices treated with caffeine and ryanodine to permeabilize ASM cells to Ca²⁺ .
  
  
  RESULTS
  The TAS2R10 agonists dilated airways constricted by either MCh or 5HT, accompanied by inhibition of agonist-induced Ca²⁺ oscillations. However, in non-contracted airways, TAS2R10 agonists, at concentrations that maximally dilated constricted airways, did not evoke Ca²⁺ signals in ASM cells. Ca²⁺ increases mediated by the photolysis of caged-IP₃ were also attenuated by chloroquine, quinine and denotonium. In Ca²⁺-permeabilized ASM cells, the TAS2R10 agonists dilated MCh- and 5HT-constricted airways.
  
  
  CONCLUSIONS
  TAS2R10 agonists reversed bronchoconstriction by inhibiting agonist-induced Ca²⁺ oscillations while simultaneously reducing the Ca²⁺ sensitivity of ASM cells. Reduction of Ca²⁺ oscillations may be due to inhibition of Ca²⁺ release through IP₃ receptors. Further characterization of bronchodilatory TAS2R agonists may lead to the development of novel therapies for the treatment of bronchoconstrictive conditions.
authors.affiliation: Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA, USA.
authors.forename: Xiahui
authors.initials: X
authors.lastname: Tan
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Sanderson
mesh_terms: D000403:Airway Resistance / Q000187:drug effects; D000818:Animals; D001993:Bronchodilator Agents / Q000494:pharmacology*; D002110:Caffeine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000737:chemistry / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects*; D002738:Chloroquine / Q000494:pharmacology*; D004351:Drug Resistance / Q000187:drug effects; D005260:Female; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000819:agonists / Q000378:metabolism; D008168:Lung / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000737:chemistry / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D011803:Quinine / Q000494:pharmacology*; D043562:Receptors, G-Protein-Coupled / Q000819:agonists* / Q000378:metabolism; D012433:Ryanodine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D013649:Taste
chemical_list: D001993:Bronchodilator Agents; D002121:Calcium Channel Blockers; D053496:Inositol 1,4,5-Trisphosphate Receptors; D010726:Phosphodiesterase Inhibitors; D000644:Quaternary Ammonium Compounds; D043562:Receptors, G-Protein-Coupled; C000592154:Tas2r107 protein, mouse; D012433:Ryanodine; D002110:Caffeine; D015544:Inositol 1,4,5-Trisphosphate; D002738:Chloroquine; D011803:Quinine
keywords: 2-photon microscopy; TAS2R; asthma; mouse lung slice; β2-adrenergic receptor agonists