Effects of hydrogen peroxide and hydroxyl radicals on the cytosolic side of a non-selective cation channel in the cultured human bronchial epithelial cell line 16HBE14o-.
Respiratory tissues can be damaged by the exposure of airway epithelial cells to reactive oxygen species (ROS) that generate an 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, non-selective cation channel (NSC(Ca)) which might participate in the transepithelial Na+ fluxes involved in the maintenance of the cytosolic [Na+] ([Na+]i). We identified and characterized NSC(Ca) in inside-out excised membrane patches from cells of the human bronchial cell line 16HBE14o- and exposed the cytoplasmic side of NSC(Ca) to H2O2 or *OH created in front of the patch pipette. In these cells, the NSC channel was Ca2+ (above 0.1 microM) and voltage dependent. The channel's low open probability ( P(o)) at hyperpolarized voltages increased rapidly to a very high value upon short exposure (seconds) to *OH or to H2O2 in a bath solution containing millimolar [Ca2+]. This sensibility to ROS was reversible on wash-out of the oxidants. Long exposure (several minutes) to *OH in a bath solution containing 10(-7) M Ca2+ activated the channel irreversibly, a finding that has pathophysiological implications. The functioning of the NSC(Ca) protein channel may be modified by the intracellular redox status and the reversibility of the sensitivity to ROS depends on [Ca2+]i. The role of NSC(Ca) channels in airway epithelia is not yet understood, but might conform to what might be expected of an NSC channel: increase in [Na]i following intracellular exposure to *OH or H2O2. Reversible or irreversible excessive opening of cation channels may induce gradual cellular responses, including changes in Na+/K+-ATPase activity, cell volume regulation, membrane polarization, activation of transcription factors required for the expression of genes of cytokines or chemokines, apoptosis and necrosis, thus triggering inflammation.
Jeulin
Claudette
C
Laboratoire de Cytophysiologie et Toxicologie Cellulaire, case 7073, Université Paris 7 Denis Diderot, 3ème étage, T 53-54, 2 Place Jussieu, 75251 Paris Cedex 05, France. jeulin@paris7.jussieu.fr
Dazy
Anne-Catherine
AC
Marano
Francelyne
F
D002118:Calcium / Q000378:metabolism; D002412:Cations / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004594:Electrophysiology; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D017665:Hydroxyl Radical / Q000494:pharmacology*; D007473:Ion Channels / Q000378:metabolism*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D016877:Oxidants / Q000494:pharmacology*; D020545:Respiratory Mucosa / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D002412:Cations; D007473:Ion Channels; D016877:Oxidants; D017665:Hydroxyl Radical; D006861:Hydrogen Peroxide; D002118:Calcium