Connexin45 (alpha 6) expression delineates an extended conduction system in the embryonic and mature rodent heart

We previously demonstrated that alpha 6 (Cx45), one of the three connexins of the mammalian myocardium, is preferentially expressed in the peripheral portion of the ventricular conduction system in rats and mice. Here we repo rt that alpha 6 is also prominently immunolocalized in the atrioventricular node and His bundle of these species. The distribution of immunolocalized alpha 6 reveals that the node and bundle form part of an extended central c onductive network circumscribing the AV and outflow junctional regions of t he fetal, and less continuously, the adult heart. Of the three cardiac conn exins, alpha 6 is the isoform most continuously expressed by conduction tis sues, and may thus account for the recently reported viability of the alpha 5 (Cx40) knockout mouse. it is concluded that alpha 6 expression is a defi ning feature of the heterogenous tissues comprising the atrioventricular co nduction system of the rodent heart. (C) 1999 Wiley-Liss, Inc.