Epithelial anion secretion of human bronchial ciliary epithelium

Background: Airway epithelia play key roles in maintaining the volume and composition of airway surface liquid by regulating trans-epithelial ion transport. However, little information is available on ion transport in upper airway epithelia. Objectives: To clarify the anion transport such as Cl-and HCO3-in human bronchial ciliary epithelium cells. Methods: Airway cells were collected by brushing bronchus during bronchoscopy, after purification of progenitor cells, air liquid interface cultured and induced differentiation into ciliated cells. Trans-epithelial ion transport of airway epithelia was analyzed measuring the short circuit current (Isc) and surface pH using surface enhanced Raman spectroscopy Results: In human bronchial ciliary epithelia, the amount of anion secretion was equal to that of Na+absorption. To focus on the anion transport, experiments were carried out under a condition of blocking Na+absorption by benzamil. Under a Cl-/HCO3--containing condition, the basolateral addition of DIDS, a blocker of anion exchanger, Na+/bicarbonate cotransporters and Cl- channels, decreased Isc. Under a Cl--free HCO3--containing condition, Isc was smaller than that under a Cl-/HCO3--containing condition. Finally, under a HCO3--free Cl--containing condition, Isc was smaller than that under a Cl-/HCO3--containing condition and similar to that under a Cl--free HCO3--containing condition. Apical surface pH showed a decreasing trend after addition of DIDS, NPPB, and a Cl--free HCO3--containing solution. Conclusion: Human bronchial ciliary cells secrete not only Cl-but also HCO3-via cooperationbetween Cl- channel and anion exchanger, contributing to control of the volume and composition of airway surface liquid.