Periciliary fluid balance is maintained by the coordination of
sodium and
chloride channels in the apical membranes of the airways. In the absence of the
cystic fibrosis transmembrane regulator (CFTR),
chloride secretion is diminished and
sodium reabsorption exaggerated. ClC-2, a pH- and voltage-dependent
chloride channel, is present on the apical membranes of airway epithelial cells. We hypothesized that ClC-2 agonists would provide a parallel pathway for
chloride secretion. Using nasal potential difference (
NPD) measurements, we quantified
lubiprostone-mediated Cl(-) transport in sedated
cystic fibrosis null (gut-corrected), C57Bl/6, and A/J mice during nasal perfusion of
lubiprostone (a putative ClC-2 agonist). Baseline,
amiloride-inhibited,
chloride-free
gluconate-substituted Ringer with
amiloride and low-
chloride Ringer plus
lubiprostone (at increasing concentrations of
lubiprostone) were perfused, and the
NPD was continuously recorded. A clear dose-response relationship was detected in all murine strains. The magnitude of the
NPD response to 20 muM
lubiprostone was -5.8 +/- 2.1 mV (CF, n = 12), -8.1 +/- 2.6 mV (C57Bl/6 wild-type, n = 12), and -5.3 +/- 1.2 mV (AJ wild-type, n = 8). A cohort of ClC-2 knockout mice did not respond to 20 muM
lubiprostone (n = 6, P = 0.27). In C57Bl/6 mice, inhibition of CFTR with topical application of CFTR inhibitor-172 did not abolish the
lubiprostone response, thus confirming the response seen is independent of CFTR regulation. RT-PCR confirmed expression of ClC-2
mRNA in murine lung homogenate. The direct application of
lubiprostone in the CF murine nasal airway restores nearly normal levels of
chloride secretion in nasal epithelia.