Reversible chemical modification by MTS at cysteine residues lining the Cx26 pore. (A) MTSES modification at D50C. (Left) Current traces from an oocyte expressing Cx26 D50C hemichannels in response to a depolarizing pulse from −80 to 0 mV. Black trace is the current before modification. Orange trace is a representative trace in the presence of MTSES after reaching the maximal effect of the modification. Blue trace is the current after wash off of MTSES. (Right) Time course of the maximal tail currents in the absence, the presence, and after wash off of MTSES. Solid blue line represents single-exponential fit for recovery from modification. (B and C) The corresponding data for MTSES modification at positions D46C and G45C, respectively. Experimental procedure as described in A. All traces were obtained in the presence of 0.25 mM of extracellular Ca²⁺.