Cardiac connexins Cx43 and Cx45: formation of diverse gap junction channels with diverse electrical properties

HeLa cells expressing rat connexin43 (Cx43) and/or mouse Cx45 were studied with the dual voltage-clamp technique. Different types of cell pairs were established and their gap junction properties determined, i.e. the dependence of the instantaneous and steady-state conductances (g(j,insb) g(j,ss)) on the transjunctional voltage (V-j) and the kinetics of inactivation of the gap junction current (I-j). Pairs of singly transfected cells showed homogeneous behaviour at both V-j polarities. Homotypic Cx43-Cx43 and Cx45-Cx45 cell pairs yielded distinct symmetrical functions g(j,inst)=f(V-j) and g(j,ss)=f(V-j). Heterotypic Cx43-Cx45 preparations exhibited asymmetric functions g(j,inst)=f(V-j) and g(j,ss)=f(V-j) suggesting that connexons Cx43 and Cx45 gate with positive and negative V-j, respectively. Preparations containing a singly (Cx43 or Cx45) or doubly (Cx43/45) transfected cell showed quasihomogeneous behaviour at one V-j polarity and heterogeneous behaviour at the other polarity. The former yielded Boltzmann parameters intermediate between those of Cx43-Cx43, Cx45-Cx45 and Cx43-Cx45 preparations; the latter could not be explained by homotypic and heterotypic combinations of homomeric connexons. Each pair of doubly transfected cells (Cx43/Cx45) yielded unique functions g(j,inst)=f(V-j) and g(j,ss)=f(V-j). This can not be explained by combinations of homomeric connexons. We conclude that Cx43 and Cx45 form homomeric-homotypic, homomeric-heterotypic channels as well as heteromeric-homotypic and heteromeric-heterotypic channels. This has implications for the impulse propagation in specific areas of the heart.