Hydrogen peroxide-induced current in Xenopus oocytes: Current characteristics similar to those induced by the removal of extracellular calcium

The effects of hydrogen peroxide (H₂O₂) exposure on Xenopus oocytes were examined. An application of 1μL of 10% H₂O₂ to oocytes voltage-clamped in 1mL of Modified Barth Saline (MBS: final concentration of 0.01% H₂O₂) induced a transient ionic current. This H₂O₂-induced current, however, was not transient but long-lasting in a Ca²⁺-free medium. The H₂O₂-induced current was independent of increases in intracellular calcium. Intriguingly, the H₂O₂-induced current was similar in signature to one stimulated by the removal of extracellular calcium (Ca_o²⁺-inactivated current). Both currents (a) were inactivated by 1.5mM LaCl₃, GdCl₃, CdCl₂, NiCl₂, CaCl₂, or MgCl₂, but not by LiCl or KCl, (b) exhibited reversal potential shifts to more positive values with increasing external NaCl, (c) showed linear voltage-current (I-V) relationships, and (d) were reversibly inhibited by two chloride channel blockers, 200μM 5-nitro-2-(3-phenylpropylamino)-benzoic acid and 250μM niflumic acid. Additionally, H₂O₂ was still able to induce current in oocytes loaded with either catalase or N-acetyl-L-cysteine, H₂O₂ scavengers. These results imply that H₂O₂ induces this ionic current possibly through the activation of Ca_o²⁺-inactivated channels by an extracellular mechanism.