title: Anion selectivity of apical membrane conductance of Calu 3 human airway epithelium.
abstract: Anion selectivity of the cystic fibrosis conductance transmembrane conductance regulator (CFTR) and other channels and parallel pathways expressed endogenously in apical membranes of polarized Calu-3 epithelial monolayers was studied under control conditions and during cAMP stimulation. Basolateral membranes were eliminated using alpha-toxin. The cAMP-stimulated, gradient-driven currents had the sequence Br>/=Cl>/=NO3>SCN> I>/=F>formate>HCO3>acetate>propionate=butyrate=ATP= PPi=PO4=SO4=0. Selectivity of parallel cAMP-independent pathway(s) was Br>Cl=SCN=NO3>I>formate=F >HCO3>acetate>propionate. SCN, I, F or formate blocked cAMP-stimulated, but not control, Cl currents. Anions >0.53 nm in diameter were impermeant, suggesting that the apical CFTR channel has a limiting diameter of 0.53 nm. The selectivity, blocking patterns and pore size of the cAMP-stimulated conductance pathway were very similar to those in previous reports in which CFTR was heterologously expressed in non-epithelial cells. Thus, CFTR appears to be the major apical anion conductance pathway in Calu-3 cells, and its conduction properties are independent of the expression system. CFTR in Calu-3 cells also conducts physiologically relevant anions, but not ATP, PO4 or SO4. A pathway parallel (probably a tight junction) showed a different selectivity than CFTR.
authors.affiliation: Department of Molecular and Cell Biology, 231 Life Science Addition, University of California at Berkeley, Berkeley, CA 94720-3200, USA.
authors.forename: B
authors.initials: B
authors.lastname: Illek
authors.forename: A W
authors.initials: AW
authors.lastname: Tam
authors.forename: H
authors.initials: H
authors.lastname: Fischer
authors.forename: T E
authors.initials: TE
authors.lastname: Machen
mesh_terms: D000230:Adenocarcinoma; D000838:Anions; D001639:Bicarbonates / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism*; D002463:Cell Membrane Permeability; D000242:Cyclic AMP / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D004553:Electric Conductivity; D004847:Epithelial Cells / Q000648:ultrastructure; D005227:Fatty Acids / Q000378:metabolism; D006801:Humans; D008168:Lung / Q000648:ultrastructure*; D008175:Lung Neoplasms; D009566:Nitrates / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D011422:Propionates / Q000378:metabolism; D013861:Thiocyanates / Q000378:metabolism; D014407:Tumor Cells, Cultured
chemical_list: D000838:Anions; D001639:Bicarbonates; C505032:CFTR protein, human; D005227:Fatty Acids; D009566:Nitrates; D010710:Phosphates; D011422:Propionates; D013861:Thiocyanates; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000242:Cyclic AMP; C031760:thiocyanate