Extracellular Alkalinization Stimulates Calcium-activated Chloride Conductance in Cystic Fibrosis Human Airway Epithelial Cells

Abstract

Background: The pH of the airway surface liquid (ASL) plays a pivotal role in maintaining the proper function of the respiratory epithelium. In patients with cystic fibrosis (CF) acidic ASL has been observed. Thus, alkalinization of ASL itself might be beneficial in CF. The aim of this study was to investigate the role of extracellular pH (pH_o) on the alternative Ca²⁺-activated Cl^- channels (CaCCs) in CF airway epithelial cells. Methods: The [Ca²⁺]_i and viability of CF airway epithelial cells (IB3-1) were assessed using Fluo-3/AM and YO-PRO-1 fluorescent dyes, respectively. Ion currents were detected in whole-cell configuration using the patch clamp technique. Results: Extracellular alkalinization (pH_o 8.2) stimulated Ca²⁺ entry and inward currents in low Na⁺ containing medium. The inward currents were blocked by the removal of extracellular Ca²⁺, chelating cytosolic Ca²⁺, as well as by the application of niflumic acid and DIDS. While Zn²⁺ promoted sustained Ca²⁺ entry in pH_o-dependent manner, it inhibited the anion conductance. The low external Na⁺ concentrations and alkaline pH_o were well tolerated by the cells. Conclusions: Stimulation of CaCCs could be achieved by alkalinization of the extracellular environment in CF airway epithelial cells. Zn²⁺ directly blocked, however indirectly enhanced the activity of Cl^- conductance.