Background. Targeting the airway surface liquid (ASL) pH in Cystic Fibrosis (CF) could potentially restore bacterial killing, ASL hydration and mucociliary clearance. CFTR and the non-gastric H+/K+-ATPase ATP12A have been implicated in ASL pH regulation but other transporters and channels might also be involved. We have shown that the Proton Pump Inhibitor (PPI), esomeprazole (Eso), increased ASL pH in CF cells via the downregulation of ATP12A but that it also acutely induced an intracellular acidification that was ATP12A-independent1. Our current work focuses on identifying the H+ transporter acutely targeted by Eso and testing other PPIs as well as potassium-competitive acid blockers (P-CABs) on pH homeostasis. Methods. Primary CF human airway epithelial cells (hAECs) were grown on semi-permeable supports under thin-film condition. ASL pH was measured using a mixture of dextran-coupled pHrodo and AlexaFluor488, in the presence of vehicle control (DMSO) or test compounds; the PPI omeprazole (OME, 300 µM), the P-CAB TAK-438 (TAK, 100 µM) or ZnCl2 (300 µM). Moreover the activity of H+-ATPases, H+ exchangers or H+ channels were assessed using intracellular pH (pHi) measurements after loading the cells with BCECF-AM (5 µM, 60 min). Results. Neither the Na+-H+ Exchanger (NHE, inhibited by EIPA) nor the V-ATPase (inhibited by Bafilomycin A1) were active in the apical membrane of CF hAECs. Although the putative H+ channel blocker Diphenhydramine hydrochloride (DPH) had no effect on pHi (ΔpHi= 0.009±0.002, n=3), ZnCl2 induced a dose-dependent acidification, suggesting that the voltage gated H+ channel HVCN12 was active under resting conditions. Although not significant, inhibition of the H+ channel by overnight apical exposure to ZnCl2 induced an increase in ASL pH of CF hAECs (CTL: 7.08±0.08 vs. ZnCl2: 7.26±0.09, n=4, p=0.07). OME induced a decrease in pHi (ΔpHi = -0.16 ± 0.04, n=3) that was not significantly different from the one observed after apical exposure to Eso (ΔpHi= -0.12±0.01, n=3). However, the P-CAB TAK showed no effect on pHi (ΔpHi= 0.03±0.02, n=3). Preliminary results using these molecules on ASL pH confirmed the effect of OME and the lack of effect of TAK. Conclusion. Considering the reversibility of Eso and OME on pHi, the absence of an appropriate acidic environment required for their activity and the lack of effect of the TAK on pHi, the gastric H+/K+-ATPase is unlikely to be a target for the modulation of H+ secretion in primary CF hAECs. However, this study has identified HVCN1 as a potential H+ transporter at the surface of CF airway cells that is targeted by PPIs. Considering the demonstrated benefits of PPIs against bacterial and viral infections, oxidative stress and inflammatory processes in other chronic airway diseases, we propose that the inhibition of multiple H+ transporters by the use of PPIs (potentially combined with future identified inhibitors) in CF airways might help alleviate CF lung pathophysiology.