title: Lubiprostone targets prostanoid EP₄ receptors in ovine airways.
abstract: OBJECTIVE
  Lubiprostone, a prostaglandin E₁ derivative, is reported to activate ClC-2 chloride channels located in the apical membranes of a number of transporting epithelia. Lack of functioning CFTR chloride channels in epithelia is responsible for the genetic disease cystic fibrosis, therefore, surrogate channels that can operate independently of CFTR are of interest. This study explores the target receptor(s) for lubiprostone in airway epithelium.
  
  
  METHODS
  All experiments were performed on the ventral tracheal epithelium of sheep. Epithelia were used to measure anion secretion from the apical surface as short circuit current or as fluid secretion from individual airway submucosal glands, using an optical method.
  
  
  RESULTS
  The EP₄ antagonists L-161982 and GW627368 inhibited short circuit current responses to lubiprostone, while EP₁(,)₂(&)₃ receptor antagonists were without effect. Similarly, lubiprostone induced secretion in airway submucosal glands was inhibited by L-161982. L-161982 effectively competed with lubiprostone with a K(d) value of 0.058 µM, close to its value for binding to human EP₄ receptors (0.024 µM). The selective EP₄ agonist L-902688 and lubiprostone behaved similarly with respect to EP₄ receptor antagonists. Results of experiments with H89, a protein kinase A inhibitor, were consistent with lubiprostone acting through a G(s) -protein coupled EP₄ receptor/cAMP cascade.
  
  
  CONCLUSIONS
  Lubiprostone-induced short-circuit currents and submucosal gland secretions were inhibited by selective EP₄ receptor antagonists. The results suggest EP₄ receptor activation by lubiprostone triggers cAMP production necessary for CFTR activation and the secretory responses, a possibility precluded in CF tissues.
authors.affiliation: Department of Medicine, University of Cambridge, Addenbrooke's Hospital, UK. awc1000@cam.ac.uk
authors.forename: A W
authors.initials: AW
authors.lastname: Cuthbert
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000527:Alprostadil / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D003550:Cystic Fibrosis / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology; D006801:Humans; D000068238:Lubiprostone; D058990:Molecular Targeted Therapy; D058309:Receptors, Prostaglandin E, EP4 Subtype / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000187:drug effects / Q000378:metabolism*; D012756:Sheep; D013876:Thiophenes / Q000378:metabolism / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects* / Q000378:metabolism; D014230:Triazoles / Q000378:metabolism / Q000494:pharmacology
chemical_list: D000090007:CLC-2 Chloride Channels; D018118:Chloride Channels; C508711:L-161982; D058309:Receptors, Prostaglandin E, EP4 Subtype; D013876:Thiophenes; D014230:Triazoles; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000068238:Lubiprostone; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D000527:Alprostadil