Heterogeneity of I-V relations observed for human Cx26 undocked hemichannels in Xenopus oocytes obtained with outside-out patch-clamp recordings in 100 mM of symmetric KCl. Five I-V relations ranging from slight inward to slight outward are illustrated. (A) Inward/sigmoidal I-V relation obtained with a ±150-mV voltage ramp. 2 of 10 sequential current traces from one record are superimposed. Current traces from −110 to 100 mV show the open-channel I-V relation. (B) Slightly inward I-V relation obtained with a ±70-mV voltage ramp. 3 of 10 sequential traces are superimposed. (C) Linear I-V relation obtained with a ±150-mV voltage ramp. 2 of 10 sequential current traces are superimposed. Current traces are shown from −125 to 100 mV. (D) Slightly outward I-V relation obtained with a ±70-mV voltage ramp. 2 of 10 sequential current traces are superimposed. (E) Outward I-V relation obtained with a ±70-mV voltage ramp. 2 of 10 sequential current traces are superimposed. In all cases, the single-channel records display both forms of voltage-dependent gating reported for Cx26 undocked hemichannels (González et al., 2006; Sánchez et al., 2010). Loop- or slow-gating transitions that can result in full channel closure were observed at large inside negative potentials, and Vj- or fast-gating transitions that result in closure to subconductance states were observed at inside positive potentials. These events correspond to the upward current deflections from the fully open state at negative potentials and downward deflections from the fully open state at positive potentials, respectively, in the records shown. Full channel closures at negative potentials were used to subtract leak conductance in single-channel records.
