Ultrastructural study of the myocardial wall of the atrio-ventricular canal during the development of the embryonic chick heart.
In the early stages of chick embryo development (days 3-5) the myocardium of the atrio-ventricular canal (AV) is continuous with the atrial and ventricular muscles; however, interruption of muscular continuity is observed at later stages (from day 6 to day 8). The most relevant event occurring at the AV canal region is the dissociation of the myocytes due to the loss of their cellular attachments, rather than an invasion of connective tissue cells (endocardial and sub-epicardial) located on both sides of the myocardium. In this study, particular attention was paid to the sequential changes that take place in the myocardium of this region, these being (1) a reduction in the number of desmosomes and intercalated discs with the subsequent appearance of large, inter-cellular spaces between myocytes; (2) migration of these cells through a complex extra-cellular matrix, to which it appears to be closely related, suggesting that the macromolecules of this matrix may be being synthesized by the myocytes, and may take part in the process of cardiac cell separation; (3) incorporation of the myocytes in the developing tricuspid valve, where they co-exist with fibroblasts. The results of the study correspond remarkably well to those previously carried out on the left AV canal myocardium, suggesting that the behaviour of the muscle is the same, at all points around the AV canal.
D000818:Animals; D002642:Chick Embryo / Q000254:growth & development*; D005347:Fibroblasts / Q000648:ultrastructure; D006321:Heart / Q000196:embryology*; D006801:Humans; D007365:Intercellular Junctions / Q000648:ultrastructure; D008854:Microscopy, Electron; D009206:Myocardium / Q000648:ultrastructure*; D014927:Wolff-Parkinson-White Syndrome / Q000196:embryology