Dysfunction of the cystic fibrosis transmembrane regulator (CFTR) is associated with diminished duodenal HCO₃⁻ secretion, despite a reported lack of clinical duodenal ulceration in affected subjects. We hypothesized that duodenal epithelial cells expressing a mutant CFTR have enhanced resistance to acid-induced injury. To test this hypothesis, we measured duodenal epithelial cell intracellular pH (pH_i), injury, and acid back-diffusion in response to a luminal acid challenge in transgenic mice.

A murine colony was established for the CFTR ΔF508 (ΔF) mutation. Epithelial cell pH_i was measured by microscopy with a trapped, fluorescent pH-sensitive dye in living C57BL/6 and ΔF/ΔF, +/ΔF, and +/+ mice. In vivo confocal microscopy confirmed the localization of the dye in the cytoplasm of the epithelial cells. Epithelial injury was measured fluorometrically using propidium iodide. Duodenal epithelial bicarbonate secretion and proton permeability were measured by back-titration. Bicarbonate secretion and acid back-diffusion were measured in a perfused duodenal loop.

Basal and post-acid exposure bicarbonate secretion were reduced in ΔF/ΔF mice, although acid back-diffusion was similar to controls. Epithelial pH_i of CFTR ΔF/ΔF mice during luminal acid exposure was significantly higher than pH_i in +/ΔF, +/+, or C57BL/6 mice. Acid-related epithelial injury was markedly less in ΔF/ΔF mice in comparison with the other groups.

Increased cellular buffering power of the epithelial cells of ΔF/ΔF mice likely protects against acidification and injury during acid exposure. We speculate that this protective mechanism partially underlies the perceived relative lack of peptic ulceration in patients affected by cystic fibrosis.