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.show $132#e. the dependence of the instantaneous and steady-state conductances (g_j,inst, 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 quasi-homogeneous 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. [ABSTRACT FROM AUTHOR]