Membrane currents induced by voltage steps from −60 to +60 mV at a rate of five/minute in oocytes expressing wt Panx1 (A and B) or Panx1 C426S. (A) 100 µM MBB induced a twofold response in wt Panx1 channels consisting of a reversible and an irreversible component (arrows). The reversible component was inducible by a subsequent application of MBB. The irreversible component was used to assess channel inhibition in all subsequent figures. (B) PEG400 and PEG600 at 1 mM caused a similar reversible channel inhibition as MBB. (C) 100 µM MBB applied to Panx1 C426S channels exclusively caused the reversible inhibition. (D) Quantitative analysis of irreversible inhibition of membrane currents by 100 µM MBB in oocytes expressing wt Panx1 and its cysteine replacement mutants C426S, C40S, C136S, C215S, C227S, and C346S.