The role of the basolateral outwardly rectifying chloride channel in human airway epithelial anion secretion

The purpose of this study was to characterize basolateral anion channels in Calu-3 and normal human bronchial epithelial cells, and their role in anion secretion. Patch clamp studies identified an outwardly rectifying Cl- channel (ORCC), which could be activated by the adenosine receptor agonist 5'-(N-ethylcarboxamido)adenosine (NECA). Short-circuit current measurements revealed that NECA activates a basolateral, but not an apical, anion conductance sensitive to 4,4'-diisothiocyanatostilbene-2, 2'-disulfonic acid, and to 9-anthracenecarboxylic acid, but not to 4,4'-dinitrostilbene-2,2'-disulfonic acid. Apical membrane permeabilization studies confirmed the presence of basolateral anion channels, established their halide permeability sequence (Cl- much greater than Br- >> I-), and demonstrated their outwardly rectifying nature. Experiments using H-89, forskolin, and Ht31 demonstrated that adenosine receptor dependent activation of basolateral ORCC was cAMP- and potentially A-kinase anchoring protein-dependent. Neither BAPTA-AM treatment nor basolateral Ca2+ removal had any effect on the activation of these channels. Anion replacement and Cl-36(-) flux studies show that Calu-3 cells primarily secrete HCO3- when stimulated with NECA, and that Cl- secretion can be stimulated by blocking basolateral ORCC, whereas normal human bronchial epithelial cells exclusively secrete Cl- under all conditions studied. We propose a novel model of anion secretion in which ORCC recycles Cl- across the basolateral membrane, allowing preferential HCO3- secretion.