Heterotypic gap junction channels (connexin26 - connexin32) violate the paradigm of unitary conductance

Human HeLa cells transfected with mouse DNA coding for connexin26 (Cx26) or connexin32 (Cx32) were used to examine the properties of heterotypic Cx26 - Cx32 gap junction channels. Intercellular current flow was examined in induced cell pairs by means of the dual voltage-clamp method. We found that Cx26 - Cx32 channels exhibit voltage-dependent conductances, γ_j: γ_j(main state) increases with increasing positivity at the cytoplasmic aspect of the Cx26 connexon and decreases with increasing negativity (slope: 32 pS/100 mV; γ_j γ_j(main state) reaches 48 pS as V _j approaches 0 mV); γ_j(residual state) with a similar V_j-dependence is present when the cytoplasmic end of Cx26 connexon is positive, but absent when it is negative. The single channel data provide an explanation for the asymmetric relationships between the gap junction conductance, g_j, and V_j. The results are consistent with the notion that docking of two connexons co-determines the biophysical properties of a gap junction channel.