(A and B) Plots of normalized tail current versus time recorded from the recipient cells after cAMP injection into the source cell for cell pairs expressing Cx43 (•): gj = 19 nS (A), and 2 nS (B); Cx26 (▾): gj = 25 nS (A), and 8 nS (B); and Cx40(○): gj = 22 nS (A) and 10 nS (B). SpIH activation time, t corresponds to the time when SpIH current reaches saturation in the recipient cell. The first order regression over the linear part of the plots (dashed line shown in Cx40 plot, A) was used to determine current activation rate ΔI/Δt. (C) Summarized plots of the SpIH tail current activation rate (ΔI/Δt) versus junctional conductance for Cx43 (•), Cx26 (▾), and Cx40(○). The solid lines correspond to the first order regressions with the following slopes: (30.0 ± 2.5) · 10−4 s−1/nS for Cx43, (7.3 ± 0.6) · 10−4 s−1/nS for Cx26, and (4.8 ± 1.1) · 10−4 s−1/nS for Cx40. The dashed lines are the 95% confidence intervals. The experiments were performed in the presence of IBMX and 2’,5′ dideoxyadenosine. Insert: current activation rate (ΔI/Δt) versus channel number for all three connexins with slopes of (1.6 ± 0.1) · 10−4 s−1/channel for Cx43 (•), (0.8 ± 0.07) · 10−4 s−1/channel for Cx26 (▾), and (0.6 ± 0.1) · 10−4 s−1/channel for Cx40 (○).
