Figure 3.

Confocal micrographs of sections through a mouse heart at embryonic day (E) 17.5 (A,B), one-day-old neonatal heart (C) and adult heart (D). The atrioventricular node of the E17.5 heart (A) labels positively for connexin45 (Cx45) (green), and a domain within this region is also positive for connexin40 (Cx40) (red). Colocalization of the two connexins shows up as yellow spots. Both Cx45 (green) and Cx40 (red) are localized to the atrioventricular bundle (AVB) and bundle branches (B) of the E17.5 heart. The area of Cx45 expression is larger than the area of Cx40 expression. Yellow spots represent colocalization of the labelling for both connexins. The same pattern of labelling is observed for the one-day neonatal heart (C). The Cx40 (red) label is almost all colocalized with Cx45 label (green), giving the orange-yellow spots within a region positive for Cx45 alone. Connexin43 (Cx43) (blue) is present only in the working myocytes of the interventricular septum. In the adult heart (D) the region of Cx45-only expression in the AVB/bundle branch region is not as great as in the embryonic or neonatal hearts, and the colocalization of Cx45 (green) and Cx40 (red) appears more complete, although some cells express Cx45 only (arrows). Bar marker = 50 μm. RRB Right bundle branch