Effect of oxidizing conditions on S312C channels. (A) After perfusion of reducing agent from the cis compartment (first downward arrow; break in record is 250 s), there is a gradual decline in current that is dramatically accelerated by the addition of 0.15% H₂O₂ to both sides of the bilayer (second downward arrow). The addition of 10 mM DTT trans restores the current to the level observed before oxidation. Break in record just before DTT addition is 110 s. (B) After H₂O₂ exposure, channels exhibit minimal gating at −60 mV. Current traces before (solid line) and after (gray line) exposure to H₂O₂, with the latter normalized as described above. Trace following DTT addition is indistinguishable from baseline trace.