Conduction characteristics affected by histological
features in the AV junction
The principal connexin in the working atrial and ventricular myocardium
is Cx43, with medium conductance.2,4,6 The CN shows
low expression levels of Cx43 in humans and
animals.4,13 However, Cx40 expression (at both the
mRNA and protein levels) is high in the CN and PB, where it is
implicated in facilitating fast conduction in humans and
rats.3,10 Cx45 is the predominant connexin expressed
in the mammalian AVN.14 Thus, connexin expression
could be used as a marker to recognize different conduction cell types.
Moreover, connexins dominate electronic conduction, which provides
approximately 30%of the conduction velocity. Another approximately 70%
is dominated by ion channels.15 The RN that we
describe in this study displayed the same pattern of connexin isoform
expression as the CN and INE. Immunohistochemical labeling of the
Nav1.5, Cav3.1 and HCN4 channels showed
nearly equal expression of these ion channels in the CN, INE and RN
(Figure 5D), indicating that these areas have highly uniform and
conserved conduction properties. These data suggest that the RN and its
connection with the CN may have the same conduction properties as the CN
and INE, exhibiting relatively slow conduction.