Irreversible maleimide modification at cysteine residues lining the pore. (A) Comparison of the chemical structures of MTSES and maleimide ES. (B) Time course of the peak tail current in the absence (black), the presence (red), or after wash off (blue) of maleimide ES for modification of D50C hemichannels expressed in Xenopus oocytes. (C) Maleimide ES modification at positions G45C, as described in A.