Role of the Carboxyl Terminal of Connexin43 in Transjunctional Fast Voltage Gating

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Abstract
Previous studies show that chemical regulation of connexin43 (Cx43) gap junction channels depends on the integrity of the carboxyl terminal (CT) domain. Experiments using Xenopus oocytes show that truncation of the CT domain alters the time course for current inactivation; however, correlation with the behavior of single Cx43 channels has been lacking. Furthermore, whereas chemical gating is associated with a “ball-and-chain” mechanism, there is no evidence whether transjunctional voltage regulation for Cx43 follows a similar model. We provide data on the properties of transjunctional currents from voltage-clamped pairs of mammalian tumor cells expressing either wild-type Cx43 or a mutant of Cx43 lacking the carboxyl terminal domain (Cx43M257). Cx43 transjunctional currents showed bi-exponential decay and a residual steady-state conductance of approximately 35% maximum. Transjunctional currents recorded from Cx43M257 channels displayed a single, slower exponential decay. Long transjunctional voltage pulse...