Decreased levels of cellular rGSH decelerate or diminish reversibility of MTS modification. BSO and TBHO₂, which decrease cytoplasmic rGSH levels, decelerate and/or diminish reversibility of the MTSES modification. (A) A representative experiment for MTSES modification at position D50C. (Left) Dots show the time course of maximal tail current for an oocyte pretreated with 2 mM TBHO₂, which was then exposed to MTSES. Wash off of MTSES was in the presence of TBHO₂. (Right) Same experiment, but with 24–48-h preexposure to BSO. The tail currents were measured in the presence of 0.25 mM of extracellular Ca²⁺ after a depolarizing pulse from −80 to 0 mV. (B and C) Representative experiments for MTS modification at positions D46C and G45C, respectively, as described in A.