Inhibitory action of hydrogen peroxide on a high-resistance epithelium

The present study describes the action of H2O2 on active transporting epithelium, and the partial blockade of this action by antioxidants. The addition of increasing concentrations of H2O2 (0.80; 8.0 and 24.0 mmol/l) to the mucosal surface of isolated toad skin causes an irreversible and dose-dependent inhibition of the short circuit current (SCC) and potential difference (PD). Quantitative determination of the parameters of the electrical equivalent circuit of the skin, by means of Isaacson's amiloride test, shows that the most affected parameters were the SCC, PD and shunt conductance. When the skins were preincubated with mannitol and vitamin E, the inhibition elicited by H2O2 was partially blocked; on the other hand, when the skins were preincubated with superoxide dismutase or allopurinol, this inhibition remains unchanged. The thiobarbituric acid method was used as an indirect quantification of lipid peroxidation. The inhibitory action of H2O2 in terms of the equivalent electrical circuit and the parallel production of lipid peroxidation points to free-radical formation. Furthermore, the significant blockade of this action by some enzymatic antioxidants is in agreement with this hypothesis.