Epithelial Na+ channel and ion transport in human nasal polyp and paranasal sinus mucosa

The purpose of the present study is to characterize the ENaC-mediated Na+ absorption in human upper airway epithelia, nasal cavity, and paranasal sinus. To perform the purpose, we obtained epithelial cells from human nasal polyp (NP) and paranasal sinus mucosa (PSM) by endoscopic surgery. We measured the short-circuit current (Isc) sensitive to benzamil (a specific ENaC blocker). The benzamil-sensitive Isc (Na+ absorption) in NP was larger than that in PSM. The mRNA expression of three subunits of ENaC was as follows: α > β > γ in both tissue, NP and MS. The mRNA expression of γ subunit of ENaC in NP was larger than that in PSM, but no difference of mRNA expression of α or β ENaC subunit between NP and PSM was detected. We found correlation of the Na+ absorption to mRNA expression of γ ENaC in NP and PSM. Forskolin diminished the Na+ absorption associated with an increase in Cl- secretion. These observations suggest that: (1) human NP absorbs more ENaC-mediated Na+ than PSM, (2) expression of γ ENaC in plays a key role in the ENaC-mediated Na+ absorption in NP and PSM, and (3) cAMP diminishes the ENaC-mediated Na+ absorption by stimulating Cl− secretion (diminution of driving force for Na+ absorption) in NP and PSM.