HETEROTYPIC GAP JUNCTION CHANNELS (CONNEXIN26 OR CONNEXIN32) VIOLATE THE PARADIGM OF UNITARY CONDUCTANCE

Human HeLa cells transfected with mouse DNA coding for connexin26 (Cx2 6) or connexin32 (Cx32) were used to examine the properties of heterot ypic Cx26 - Cx32 gap junction channels. Intercellular current flow was examined in induced cell pairs by means of the dual voltage-clamp met hod. We found that Cx26 - Cx32 channels exhibit voltage-dependent cond uctances, gamma(j): gamma(j)(main state) increases with increasing pos itivity at the cytoplasmic aspect of the Cx26 connexon and decreases w ith increasing negativity (slope: 32 pS/100 mV; gamma(j)(main state) r eaches 48 pS as V-j approaches 0 mV); gamma(j)(residual state) with a similar V-dependence is present when the cytoplasmic end of Cx26 conne xon is positive, but absent when it is negative. The single channel da ta provide an explanation for the asymmetric relationships between the gap junction conductance, g(j), and V-j. The results are consistent w ith the notion that docking of two connexons co-determines the biophys ical properties of a gap junction channel.