Lubiprostone targets prostanoid EP 4 receptors in ovine airways

BACKGROUND AND PURPOSE Lubiprostone, a prostaglandin E 1 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. EXPERIMENTAL APPROACH 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. KEY RESULTS The EP 4 antagonists L‐161982 and GW627368 inhibited short circuit current responses to lubiprostone, while EP 1,2&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 EP 4 receptors (0.024 µM). The selective EP 4 agonist L‐902688 and lubiprostone behaved similarly with respect to EP 4 receptor antagonists. Results of experiments with H89, a protein kinase A inhibitor, were consistent with lubiprostone acting through a G s ‐protein coupled EP 4 receptor/cAMP cascade. CONCLUSIONS AND IMPLICATIONS Lubiprostone‐induced short‐circuit currents and submucosal gland secretions were inhibited by selective EP 4 receptor antagonists. The results suggest EP 4 receptor activation by lubiprostone triggers cAMP production necessary for CFTR activation and the secretory responses, a possibility precluded in CF tissues.