In vivo activation of CFTR-dependent chloride transport in murine airway epithelium by CNP.

Inhibitors of guanosine 3',5'-cyclic monophosphate (cGMP)-inhibited phosphodiesterases stimulate Cl- transport across the nasal epithelia of cystic fibrosis mice carrying the ΔF508 mutation [cystic fibrosis transmembrane conductance regulator (CFTR) (ΔF/ΔF)], suggesting a role for cGMP in regulation of epithelial ion transport. Here we show that activation of membrane-bound guanylate cyclases by C-type natriuretic peptide (CNP) stimulates hyperpolarization of nasal epithelium in both wild-type and ΔF508 CFTR mice in vivo but not in nasal epithelium of mice lacking CFTR [CFTR(-/-)]. With the use of a nasal transepithelial potential difference (TEPD) assay, CNP was found to hyperpolarize lumen negative TEPD by 6.1 ± 0.6 mV in mice carrying wild-type CFTR. This value is consistent with that obtained with 8-bromoguanosine 3',5'-cyclic monophosphate (6.2 ± 0.9 mV). A combination of the adenylate cyclase agonist forskolin and CNP demonstrated a synergistic ability to induce Cl- secretion across the nasal epithelium of CFTR(ΔF/ΔF) mice. No effect on TEPD was seen with this combination when used on CFTR(-/-) mice, implying that the CNP-induced change in TEPD in CFTR(ΔF/ΔF) mice is CFTR dependent.