Evidence for reduced Cl- and increased Na+ permeability in cystic fibrosis human primary cell cultures

Abstract

1. Employing a primary cell culture system and intracellular microelectrodes, we quantitated and compared the Na+ and Cl- pathways in apical membranes of normal and cystic fibrosis (CF) human airway epithelia. 2. Like the transepithelial difference (PD) in situ, the PD of CF epithelia in culture (-27 +/- 4 mV, mean +/- S.E.M.; n = 28) exceeded the PD of normal epithelia (-10 +/- 1 mV; n = 22). The raised PD principally reflected an increase in the rate of active transport (equivalent short circuit, Ieq) for CF epithelia (61 +/- 9 microA cm-2) as compared with normal epithelia (23 +/- 3 microA cm-2). No significant differences in transepithelial resistance were detected. 3. As indicated by ion replacement studies (gluconate for Cl-), the apical membrane of normal cells exhibits an apical membrane Cl- conductance (GCl) that can be activated by isoprenaline. CF cells do not exhibit an apical membrane GCl, nor can a GCl be activated by isoprenaline. 4. CF cells exhibited a larger amiloride-sensitive Ieq and amiloride-sensitive apical membrane conductance (GNa) than normal cells. Further, the amiloride-sensitive Ieq was increased by isoprenaline in CF but not normal airway epithelia. 5. Equivalent circuit analysis yielded evidence for a more positive electromotive force (EMF) across the apical membrane and a more negative EMF across the basolateral membrane of CF cells as compared with normal cells. Baseline resistances of the apical (Ra) and basolateral (Rb) membranes did not differ for normal and CF cells. 6. Estimates of the resistance of the paracellular path to ion flow (Rs) by equivalent circuit analysis or ion substitution detected no differences in Rs between CF and normal cells. 7. We conclude that abnormalities in both cellular Cl- permeability (reduced) and Na+ permeability (increased) are characteristic of the cultured CF respiratory epithelial cell. These data suggest that a defect in the regulation of apical membrane permeabilities is a central feature of this disease.