In human bronchial epithelial cells the cAMP-activated Cl- channel CFTR mediates Cl- secretion. This critical role is highlighted in cystic fibrosis, where CFTR mutations impact significantly leading to defective muco-cilliary clearance and an increased risk of infection. Previous work has suggested that the fatty acid lubiprostone (Lp) activates CFTR in ovine airway via a prostanoid receptor-dependent process [1]. In the current study the mechanism of action of Lp in human bronchial cells (16HBE14o−) was investigated. Cells were grown on permeable supports until confluent (transepithelial resistance of at least 200 Ωcm2). Inserts were mounted in an Ussing chamber with standard Krebs (basolateral side) and low Cl- Krebs (apical side). Solutions were bubbled (5% CO2), and all potential and resistance measurements corrected. 10 µA of current was injected to calculate the equivalent short circuit current (ISC). Control measurements were taken for 5 minutes and then 1 µM Lp added apically. At steady-state 10 µM CFTRinh172 was then added to provide an indication of CFTR function. This was repeated in unpaired inserts in the presence of inhibitors for EP4 receptors (GW627368X or L161,982). Statistical significance was tested using ANOVAs and assumed at the 5% level. Addition of Lp increased ISC from 10.1 ± 1.74 µA/cm2 to 26.2 ± 2.63 µA/cm2 (n=23), a mean increase of 16.1 ± 2.21 µA/cm2. In the presence of GW627368X or L161,982 the response to Lp was blunted, with mean increases of 6.26 ± 1.21 µA/cm2 (n=14) and 7.64 ± 1.98 µA/cm2 (n=9), respectively. Under control conditions CFTRinh172 reversed the increase observed with Lp, a fall of 20.2 ± 2.29 µA/cm2 (n=23). This effect of CFTRinh172 post Lp was reduced by around 50% on pre-incubation with GW627368X or L161,982. The CFTRinh172-sensitive ISC was 10.7 ± 1.79 µA/cm2 (n=14) and 9.55 ± 1.99 µA/cm2 (n=9), respectively. These data suggest that Lp activates CFTR in human airway via an EP4 receptor dependent process. Further work is needed to elucidate the downstream pathway involved and determine if any other EP receptors play a role in the response to Lp.