Heterotypic connexin50/connexin50 mutant gap junction channels reveal interactions between two hemichannels during transjunctional voltage-dependent gating.

To investigate transjunctional voltage (Vj)-dependent gating mechanisms of connexin50 (Cx50) gap junction (GJ) channels and to elucidate the relative contribution of each hemichannel of a heterotypic GJ channel to Vj-dependent gating, we performed dual voltage-clamp recordings on heterotypic GJ channels formed by Cx50 and a mutant, Cx50N9R or a chimera, Cx50-Cx36N. Our results provide evidence that the two component hemichannels interact with each other during Vj-dependent gating. Cx50/Cx50N9R heterotypic GJ channels exhibited asymmetrical Vj-dependent gating which cannot be ascribed to the function of an individual hemichannel for a certain polarity of voltage; instead it can only be ascribed to the combined effects of both hemichannels. Single GJ channel open dwell-time analyses showed that homotypic Cx50 channels adopted short-lived and long-lived open states. Heterotypic combinations of Cx50/Cx50N9R gave rise to shorter mean dwell-times when Cx50-expressing cells received relatively positive Vj, and longer mean dwell-times when positive Vj was applied at the Cx50N9R side. In contrast, Cx50/Cx50-Cx36N heterotypic channels showed asymmetrical Vj-dependent gating, which appears to be caused by enhanced and reduced Vj-gating sensitivity of Cx50-Cx36N and Cx50 hemichannels, respectively. Unitary conductance of the main open state of both types of heterotypic GJ channel cannot be simply predicted by assuming a Vj redistribution across the two hemichannels arranged in series in heterotypic GJ channels. Our data also reveal reasons for the invisibility of fast Vj-gating transitions from open to substate in homotypic Cx50N9R and Cx50-Cx36N channels.