Fig. 2.

Unitary conductance and voltage gating of Cx43 and Cx43-EGFP hemichannels. (A Upper) Single-channel events in a Cx43 cell at a holding V_m of +90 mV. Two channels were fully open just after 18 s. (Lower) Boxed regions in Upper are shown as conductances on an expanded time scale (reversal potential assumed to be 0; leakage current = 52 pA; open circles indicate 2-ms time points). a₁, A single channel opened at 1 s to a conductance of ≈220 pS and then closed to a substate of ≈75 pS. The opening was slow (>10 ms), but the closure to the substate was fast and not resolved. a₂, Slow opening to the substate. a₃, Slow opening and closing of a second channel superimposed on the substate of the first channel (redefined as zero current here). a₄, Slow closing of the substate of the first channel. a₅, Fast opening and closing of one channel superimposed on the substate of both channels. O, open state; S, substate; C, closed state. (B) Single-channel activity in a Cx43-EGFP cell; a maximum of two channels were open simultaneously. The display is as described for A.b₁–b₄, Records with higher time resolution showing only slow transitions between open and closed states. (C) All-points histograms from a₁ and b₃ showing three peaks for Cx43 and two for Cx43-EGFP. (D) Conductances of substate and main state; each point is the mean of several measurements from a different cell. The main state had the same conductance for Cx43 (220 ± 11 pS; n = 10) and Cx43-EGFP (223 ± 9 pS; n = 15). The conductance of the Cx43 substate was 77 ± 13 pS (n = 10).