| Effect of H2O2 on alveolar epithelial barrier properties. |
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Duk Joon Suh1, Se Heon Cho2, Chang Woon Kang3 |
1Department of Physiology, College of Medicine, Dong-A University, Pusan, Korea
2Department of General Surgery, College of Medicine, Dong-A University, Pusan, Korea
3Department of Internal Medicine, College of Medicine, Dong-A University, Pusan, Korea |
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| Abstract |
Background
Among the injurious agents to which the lung airspaces are constantly exposed are reactive species of oxygen. It has been widely believed that reactive oxygen species may be implicated in the etiology of lung injuries. In order to elucidated how this oxidant causes lung cell injury, we investigated the effects of exogenousH2O2 on alveolar epithelial barrier characteristics.
Methods
Rat type II alveolar epithelial cells were plated onto tissue culture-treated polycarbonate membrane filters. The resulting confluent monolayers on days 3 and 4 were mounted in a modified Ussing chamber and bathed on both sides with HEPES-buffered Ringer solution. The changes in short-circuit current (Isc) and monolayer resistance (R) in response to the exogenous hydroperoxide were measured. To determine the degree of cellular catalase participation in protection against H2O2 injury to the barrier, experiments were repeated in the presence of 20 mM aminotriazole (AT AZ, an inhibitor of catalase) in the same bathing fluid as the hydroperoxide.
Results
These monolayers have a high transepithelial resistance ( > 2000 ohm.cm2) and actively transport N a+ from apical fluid. H2O2 (0-100 mM) was then delivered to either apical or basolateral fluid. Resulting indicated that H2O2 decreased Isc and R gradually in dose.dependent manner. The effective concentration of apical H2O2 at which Isc (or R) was decreased by 50% at one hour (ED50) was about 4 mM. However, basolateral H2O2 exposure led to ED50 for Isc (and R) of about 0. 04 mM.
Inhibition of cellular catalase yielded EDso for Isc (and R) of about 0.4 mM when H2O2 was given apically, while ED50 for basolateral exposure to H2O2 did not change in the presence of AT AZ. The rate of H2O2 consumption in apical and basolateral bathing fluids was the same, while cellualr catalase activity rose gradually with time in culture.
Conclusion
Our data suggest that basolateral H2O2 may affect directly membrane component (e.g., Na+, K+ -ATPase) located on the basolateral cell surface. Apical H2O2 on the other hand, may be largely degraded by catalase as it passes through the cells before reaching these membrane components. We conclude that alveolar epithelial barrier integrity as measured by Isc and R are compromised by H2O2 being relatively sensitive to basolateral (and insensitive to apical) H2O2. |
| Key Words:
Alveolar epithelium, Pulmonary edema, H2O2, Permeability |
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