(A) LaCl3 (red bar) blocked opening events. Solution exchange artifact is shown in gray. (B) The ~9 pA events were eliminated from the all-points histogram by La3+ treatment (before LaCl3 black; after LaCl3 red) (C) La3+ treatment (red) reduced NPo to 0 (closed symbols indicate measurements at -100 mV, open symbols indicate measurements at +100 mV, n = 9). (D) MTSET forms a disulfide bond with Cys66 located within the pore of claudin-2I66C channels (Angelow and Yu, 2009). (E) Transgenic claudin-2I66C was expressed at levels similar to claudin-2WT. (F,G) MTSET dramatically reduced the number of detectable events in trans-tight junction patch clamp recordings from MDCKI cells expressing claudin-2I66C within ~20 s, but had no effect on monolayers expressing claudin-2WT. Blue bar indicates presence of MTSET (n = 8 to 16 per condition). Solution exchange artifacts are shown in gray. (H,I) NPo of MDCKI cells expressing claudin-2I66C or claudin-2WT before and after (purple) MTSET treatment (closed symbols indicate measurements at -100 mV, open symbols indicate measurements at +100 mV, n = 8 to 16 per condition). (J) Derivatization of claudin-2I66C does to affect conductance of residual events (V = –100 mV). The histogram depicts frequency of events before and after (purple) MTSET treatment.