Structural differences in the cytoarchitecture and intercalated discs between the working myocardium and conduction system in the human heart

Abstract

Working and specialized cardiac myocytes and their intercalated discs in adult human hearts without history of cardiac disease were examined by scanning electron microscopy. The NaOH/ultrasonication treatment of cardiac tissues resulted in the digestion of connective tissue and separation of intercellular junctions. Auricular and ventricular working cardiac myocytes were quasi-cylindrical in shape, bifurcated, and connected end-to-end at the intercalated discs. The intercalated discs in the working cardiac myocytes showed a stair-like profile, consisting of steps (plicate segments) and corresponding risers (interplicate segments). The ventricular myocytes, in particular, had many steps and risers. The plicate segments were filled with numerous finger-like microprojections. The strands of the myocytes in the sinoatrial node were oriented linearly, while those in the atrioventricular node formed a reticular network. The intercalated discs in both nodal cells were underdeveloped, having few microprojections. Myocytes in the atrioventricular bundle (His) and the right limb were arranged in parallel, and were characterized by the presence of slender branches. Purkinje cell strands formed reticular networks. The intercalated discs in the His-Purkinje system were irregular in appearance, and the microprojections were larger in size and smaller in number than those of working myocytes. The myocytes in the crista terminalis and surrounding the fossa ovalis resembled cells in the His-Purkinje system rather than auricular working myocytes in morphology, and may act as the internodal pathway. It is concluded that morphological differences in both the cytoarchitecture and intercalated discs were closely related with contraction and impulse propagation in the various regions of the human heart.

A distinct type of cell in myocardium: interstitial Cajal‐like cells (ICLCs)

“…Glutaraldehyde pre‐fixed specimens were washed in 0.1 mmol natrium cacodylate buffer (pH 7.4) and immersed in 6 N NaOH for 10–15 min. at 60°C to digest collagen fibres and basement membrane as previously described [44]. The specimens were washed thoroughly in PBS and post‐fixed in 1% osmium tetroxide for 1 hr.…”

Ultrastructure and Cytoarchitecture of Bachmann’s Bundle in the Mammalian Heart

“…18,19) Recently the intercalated disks in the mammalian heart were visualized three-demensionally by utilizing scanning electron microscopic techniques combined with the NaOH/ultrasonication method. [20][21][22] The intercalated disks of myocytes in the crista terminalis and surrounding the fossa ovalis were apparently different in three-dimensional architecture from those of atrial myocytes. 21) Thus, in spite of the numerous morphological studies on the working myocardium and the cardiac conduction system, relatively little attention has been paid to the BB for many years.…”

“…[20][21][22] The intercalated disks of myocytes in the crista terminalis and surrounding the fossa ovalis were apparently different in three-dimensional architecture from those of atrial myocytes. 21) Thus, in spite of the numerous morphological studies on the working myocardium and the cardiac conduction system, relatively little attention has been paid to the BB for many years. 23) Recently, it has been suggested that Bachmann's bundle pacing is effective for the prevention of atrial fibrillation (AF), 24,25) and many clinical and experimental data about AF and BB have also been reported.…”

Heterogeneous expression of connexin 43 in the myocardium of rabbit right ventricular outflow tract

“…Each gap junction channel consists of subunit proteins called connexin (Cx) (Kumar and Gilula, 1996). The number, size, and distribution of the gap junctions in the heart play an important role in determining the conduction properties of the different cardiac tissues (Vozzi et al, 1999;Miyamoto et al, 2002). In the mammalian heart, gap junctions are composed of Cx40, Cx43, Cx45 and Cx37.…”