Functional assembly of gap junction conductance in lipid bilayers: Demonstration that the major 27 kd protein forms the junctional channel

Gap junctions isolated from rat liver were incorporated into planar lipid bilayers. A channel activity that was directly dependent on voltage was recorded. Changes of pH and (Ca²⁺) had no direct effect on channel activity; however, they modulated the voltage-dependent gating of the gap junction channels differently. Single-channel fluctuations showed large scatter with peak amplitudes of 140 and 280 picoSiemmens in 0.1 M NaCl. The major protein of gap junctions (M_r of 27 kd) was also reconstituted into bilayers, giving channel properties similar to those of intact gap junctions. Polyclonal antibodies specific for this protein caused inhibition of the junctional conductance in bilayers. These data provide direct evidence that the 27 kd protein is the molecular species responsible for gap junction communication between cells.