Paradoxical effects of hydrogen peroxide on human airway anion secretion.
The present study concerns intriguing effects of hydrogen peroxide (H2O2) on cAMP-mediated anion secretion in polarized human airway epithelia. Although H2O2 applied to the apical and basolateral membrane increases short-circuit currents (ISC) with analogous properties, it has opposite effects on subsequent cAMP-activated ISC responses. Namely, forskolin (FK)-induced ISC responses were down-regulated by the apical presence of H2O2, whereas they were up-regulated by its basolateral presence. Despite this contrasting effect, oxidative stimuli from either aspect of the monolayer hindered FK-induced increments in cytosolic cAMP levels and apical membrane Cl- conductance. The site-dependent effects of H2O2 were reproduced in the responses to 8-bromo-cAMP. Estimation of the anionic composition of the ISC revealed that the FK up-regulated both bumetanide [an Na+-K+-2Cl- cotransporter (NKCC1) inhibitor]-sensitive and 4,4'-dinitrostilbene-2,2'-disulfonic acid [an HCO3--dependent anion transporter (NBC1/AE2) inhibitor]-sensitive ISC in the control, whereas the up-regulation evidently favored bumetanide-sensitive ISC in the basolateral presence of H2O2. The FK-induced NKCC1 augmentation after exposure to basolateral H2O2 was counteracted by cytochalasin D, an inhibitor of microfilament function, but not by charybdotoxin, a blocker of the intermediate conductance Ca2+-activated K+ channel, whose activation could be related to NKCC1-mediated Cl- secretion. These observations suggest that basolaterally but not apically applied H2O2 potentiates subsequent cAMP-mediated Cl- secretion by an increase in Cl- uptake via basolateral NKCC1, whose sensitivities to cAMP/protein kinase A are up-regulated, overcoming the H2O2-induced inhibition of cAMP-mediated apical anion conductance. The basolateral membrane-specific effects of H2O2 may be relevant to the basolateral cytoskeleton, which is believed to interact with NKCC1.
Department of Respiratory Medicine, Nagoya University Graduate School of Medicine, Tsurumai-cho, Showaku, Nagoya, 466-8550, Japan.
Takamasa
T
Ohashi
Yasushi
Y
Ito
Tadakatsu
T
Matsuno
Shinji
S
Sato
Kaoru
K
Shimokata
Hiroaki
H
Kume
D000838:Anions / Q000378:metabolism; D002460:Cell Line; D002712:Chlorides / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D020545:Respiratory Mucosa / Q000187:drug effects* / Q000378:metabolism*
D000838:Anions; D002712:Chlorides; D006861:Hydrogen Peroxide; D000242:Cyclic AMP