Ultrastructure of Heart Muscle

Proximal Atrioventricular Bundle, Atrioventricular Node, and Distal Atrioventricular Bundle Are Distinct Anatomic Structures With Unique Histological Characteristics and Innervation

“…The PAVB has been overlooked in conventional studies because the PAVB region is completely (Hudson,3 Figure 1). Fascicular compartmentation of the AV bridge tissues into primary fascicles are similar only to Purkinje fibers, which in fact consist of several myofibers tightly packed into small fascicles (Sommer and Jennings, 20 Figure 30) and has been directly demonstrated through the diffusion of iontophoresed Lucifer yellow. 10 Secondary fascicles are unique to the AV bridge tissues and provide an anatomic basis for multiple inputs to and through the AVN.…”

“…16 Clear perinuclear regions were found in the AV bridge myocytes. These represent glycogen storage and are a hallmark of the ventricular conduction system, which uses anaerobic glycogen metabolism, as opposed to the aerobic metabolism preferred by working myocardium, and permits delineation of this system during surgery through the Lugol's reaction (Sommer and Jennings,20 Figure 29).…”

Effects of bepridil on ventricular depolarization and repolarization of rabbit isolated hearts with particular reference to its possible proarrhythmic properties

“…According to their experiments, % prolongation of APD90 by bepridil in rabbit papillary muscles was enhanced by several times when the K+ concentration in the medium was lowered from 5.6 mM to 2.8 mM. In cardiac tissue, K+ concentration in extracellular fluid just adjacent to the myocardial cell membrane is known to vary considerably because ofthe limited rate of diffusion in narrow spaces such as the intercellular cleft or transverse tubules (Sommer & Johnson, 1979). Myocardial cells in different sites of the ventricle might, therefore, be exposed to somewhat different K+ concentrations leading to different responses to bepridil.…”

Rubidium-87 magnetic resonance spectroscopy and imaging for analysis of mammalian K+ transport

“…An additional complicating factor is a presence of various cell types in cardiac muscle, such as vascular endothelial and smooth muscle cells, fibroblasts and cells of the conducting system (Purkinje fibers). 22 However the cytoplasmic volumes of these cells are much smaller than those of contractile myocytes, which suggests that the measured uptake/efflux parameters are determined mainly by the myocytes. …”

“…In perfused or superfused muscle preparations, isotope delivery to the cells may distort uptake/washout kinetics if delivery is rate-limiting. In arterially perfused preparations of cardiac muscle, which has a high capillary density (3-4 per myocyte 22 ), the isotope or other tracers quickly penetrate the capillary wall. The in vivo index of conductance of the capillary wall is considerably higher than that of the sarcolemma: the permeability-surface area product (PS cap /PS sarc ) is 2-6.6 for K þ23, 24 and by extension for Rb þ , whose diffusion coefficient is very similar to K þ .…”