Anion selectivity of apical membrane conductance of Calu 3 human airway epithelium

• Published in: Pflügers Archiv Vol. 437; no. 6; pp. 812 - 822
• Main Authors: Illek, B, Tam, A W, Fischer, H, Machen, T E
• Format: Journal Article
• Language: English
• Published: Germany Springer Nature B.V 01.05.1999
• Subjects: Adenocarcinoma; Anions; Bicarbonates - metabolism; Cell Membrane - metabolism; Cell Membrane Permeability; Cellular biology; Cyclic AMP - pharmacology; Cystic fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator - metabolism; Electric Conductivity; Epithelial Cells - ultrastructure; Fatty Acids - metabolism; Humans; Lung - ultrastructure; Lung Neoplasms; Nitrates - metabolism; Phosphates - metabolism; Propionates - metabolism; Thiocyanates - metabolism; Tumor Cells, Cultured
• ISSN: 0031-6768; 1432-2013
• DOI: 10.1007/s004240050850

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.