High concentrations of HCO3− can normalize already formed mucus. (A) 115 mM, NaHCO3 was applied apically to mucus present on ileal explants from CF (n = 3) and WT (n = 3) mice. Mucus thickness was measured at indicated time points. (B) Confocal image of the surface of ileal explants from CF mice (n = 4), where the mucus has been exposed to 115 mM NaHCO3 for 15 min before the addition of 2 µm fluorescent beads (green) as in Fig. 1 E. Bar, 50 µm. (C) Bright field images of CF mouse ileal tissue mounted in horizontal chamber with charcoal added to visualize the mucus surface. 115 mM NaHCO3 was added to the already formed mucus on CF ileal explants and incubated for 30 min. Images show mucus before and after mucus aspiration. See Video 5. (D) Transmission electron microscopic images of surface epithelia and crypts in CftrΔF508 mouse ileum (n = 2) after 15-min treatment with 115 mM NaHCO3. Note the characteristic distension in the CF crypts. Bars, 2 µm. Arrowhead points to contact between mucus and epithelium. Data are presented as mean ± SEM.
