The CF mucus phenotype can be normalized by apical HCO₃⁻. (A) Total CF mucus thickness after CCh- and PGE₂-stimulated secretion into apical buffers containing 23, 69, 92, or 115 mM apical HCO₃⁻. (B) Remaining mucus thickness after aspiration in the presence of increasing concentrations of apical HCO₃⁻ (n = 6 for 23, 92, and apical 115; n = 3 for 69 and 115 serosal; **, P < 0.05). (C) Bright field images of CF ileal tissue with mucus secreted into 115 mM HCO₃⁻ apical buffer before and after aspiration. See Video 4 to watch the aspiration the mucus. (D) Total and remaining mucus thickness after CCh- and PGE₂-stimulated secretion into apical buffers containing 10 or 20 mM EDTA (n = 5 in all three groups; **, P = 0.008). Data are presented as mean ± SEM.