Gap junction channels of insects exhibit a residual conductance

Formation of gap junction coupled cell pairs was used to assess the basic properties of single gap junction channels. For this purpose, two single cells (clone C6/36, derived from larvae of an insect, Aedes albopictus) were manoeuvred against each other to provoke gap junction channel insertion. Intercellular current flow was measured with a dual voltage-clamp method. Utilizing this approach, we were able to demonstrate that gap junction channels, after formation, do not close completely upon application of a transjunctional voltage gradient, V_j. Instead, they exhibit a residual conductance, γ_j(residual). On average, γ_j(residual) was 64±4 pS (n=40). This corresponds to about 1/6 of the conductance of a fully open channel. The existence of γ_j(residual) explains the observation that the conductance of the entire gap junction, g_j, decreases only partially at large V_j.