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Laboratoire de Cytophysiologie et Toxicologie Cellulaire, Université Paris, Paris, France
Submitted 16 September 2004 ; accepted in final form 8 June 2005
Respiratory tissues can be damaged by the exposure of airway epithelial cells to reactive oxygen species that generate oxidative stress. We studied the effects of the hydroxyl radical ·OH, for which there is no natural intra- or extracellular scavenger, on a Ca2+-activated chloride channel (CACC) that participates in Cl secretion in the apical membrane of airway epithelial cells. We identified and characterized CACC in cell-attached and in inside-out excised membrane patches from the apical membrane of cultured nonciliated human nasal epithelial cells. In these cells, the CACC was outwardly rectified, Ca2+/calmodulin-kinase II, and voltage dependent. The channel was activated in cell-attached and inside-out patches in a bath solution containing millimolar [Ca2+] and ran down quickly. The channel was reversibly or irreversibly activated by exposure of the internal surface of the membrane to ·OH, which depended on the concentration and the duration of exposure to H2O2. CACC activity evoked by oxidative stress was inhibited by 1,3-dimethyl-2-thiurea, an antioxidant that scavenges hydroxyl radicals, and by the reduced form of glutathione. The oxidized SH residues could be close to the Ca2+/calmodulin kinase site. The reversible or irreversible activation of CACC after a period of oxidative stress without change in [Ca2+] is a new observation. CACC play a direct role in mucus production by goblet cells and may thus contribute to the pathogenesis of asthma.
endogenous chloride channels; outwardly rectifying chloride channel; cystic fibrosis transmembrane conductance regulator; airway epithelial cells
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