When all three ENaC subunits were expressed, 0.5 ��g of each subunit was transfected per well. When expressed individually, 0.75 ��g of the subunit was transfected newsletter subscribe per well. The transfected cells were lysed 24 h later using Nonidet P-40 buffer with 1�� complete EDTA-free protease inhibitor (Roche, Basel, Switzerland). The lysate was centrifuged at 16,300 g for 15 min at 4��C, and the supernatant was collected. Protein concentration was determined using the BCA assay, and 500 ��g of protein plus 0.25 mg peptide and 100 ��l of neutravidin were added to a spin column and rotated end-over-end at 4��C for 24 h (all ThermoFisher Scientific, Rockford, IL, USA). Flow-through was collected by centrifugation at 1000 g for 30 s. The beads were then washed 5 times with Nonidet P-40 buffer.

Bound protein was eluted by boiling at 95��C for 10 min in 75 ��l of 2�� LDS NuPAGE sample buffer with 1�� sample reducing agent, followed by centrifugation at 16,300 g for 2 min. Samples were resolved on 4�C12% Bis-Tris gels in MES and transferred to a nitrocellulose membrane using iBlot, setting P3 for 8 min (Invitrogen, Carlsbad, CA, USA). The membrane was probed using 1:1000 anti-V5 antibody (Invitrogen) overnight at 4��C in 3% fish gelatin in TBS-T. The blot was then incubated for 1 h at room temperature with an ECL sheep anti-mouse IgG secondary antibody and detected by ECL reagent (ThermoFisher Scientific, Waltham, MA, USA) or by incubation with a goat anti-mouse IRDye secondary antibody and analyzed by an Odyssey infrared imaging system (LI-COR Biosciences, Lincoln, NE, USA).

Deglycosylation Peptide pulldown assays were performed as described above. Samples were eluted by the addition of 100 ��l of 0.1 M sodium citrate (pH 5.5) and 0.1% SDS to the beads and incubating at 100��C for 2 min, followed by centrifugation at 16,300 g for 2 min. The samples were divided equally, and half was treated with 1 ��l of endoglycosidase H (EndoH) and incubated at 37��C for 2 min. After incubation, all samples were lyophilized and then reconstituted in 30 ��l LDS NuPAGE sample buffer with 1�� sample reducing agent (Invitrogen). Western blots were completed as described above. A concentration of 5 ��g/ml tunicamycin (Sigma-Aldrich, St Louis, MO, USA) was added to the cell transfection medium, and the cells were incubated overnight at 37��C/5% CO2.

The following day, the protocol for the peptide pulldown assay was performed as described above. ASL height measurement To label the ASL, 20 ��l PBS containing 10 kDa rhodamine dextran (0.2�C2 mg/ml; Invitrogen) was added to HBEC GSK-3 mucosal surfaces, as described previously (27). When added, peptides with or without 100 nM NE, 1 U/ml aprotinin, activated neutrophil supernatant (ANS; ref. 28), or 10 ��M sivelestat (Sigma-Aldrich) were added to the mucosal surface along with the rhodamine dextran.