(A–C) Plots of junctional conductance versus time from Cx43 (•, n = 9), Cx40 (○, n = 12), and Cx26 (▾, n = 12) expressing cell pairs, measured during the application of cAMP to the donor cell. Data represent means ± SEM. (D) Current recorded from the single SpIH-expressing cell with 20 μM cAMP in the pipette in perforated patch mode. There was no detectable SpIH current increase in perforated patch mode, and SpIH current increased dramatically when perforated patch was converted to the conventional whole cell patch clamp (around 15 min time mark). See text for details. All measurements were done in the presence of IBMX and 2’5′dideoxyadenosine.