Enzyme histochemical studies on the conducting system of the human heart

Summary In this communication, the results of applying various histochemical techniques for the localization of oxidoreductases, transferases, hydrolases and isomerases in the human heart are presented. The Purkinje fibres of the atrioventricular conducting system of the human heart differ from the myocardium proper in containing a slightly higher activity of most of the glycolytic and gluconeogenetic enzymes investigated. The relatively higher activity of 6-phosphofructokinase, the key enzyme in anaerobic carbohydrate metabolism, is especially noteworthy. On the other hand, the activities of some of the enzymes that play a part in the aerobic energy metabolism is slightly less than those in the myocardium fibres.As for the activity of the NADPH regenerating enzymes, the activity of 6-phosphogluconate dehydrogenase and malate dehydrogenase (oxaloacetate-decarboxylating) is somewhat higher, and the activity of glucose-6-phosphate dehydrogenase similar, in the Purkinje fibres compared to that in the myocardial fibres. The activity of myosin ATPase is similar for both types of fibre. Likewise, the fibres of the conducting system and of the myocardium show a similar activity of acid phosphatase, -glucuronidase, non-specific naphthylesterase and peroxidase. The neurogenic function of the conducting system of the human heart was demonstrated by the high activity of acetylcholinesterase in the Purkinje fibres and in the atrioventricular node. All these histochemical findings in Purkinje fibres are similar at widely differing levels of the conducting system.     

Gangliosides of the bovine heart impulse conducting system

The ganglioside analysis of the heart impulse conducting system was carried out, comparing it with that of ordinary myocardium. The heart impulse conducting system contained about 3-times more gangliosides than ordinary myocardium and showed a distinctly different ganglioside composition. These observations seemed to indicate that the differentiation between myoblasts and each type of cardiac muscle cell, impulse conducting system and ordinary myocardium cells, resulted in their characteristic ganglioside compositions.     

Types of anatomic correspondence between the conducting system and the heart

The principles of a quantitative determination of characteristics concerning the types of anatomical correspondence between the conduction system and the heart at its congenital malformations are presented. This makes it possible to establish that the topographoanatomical type of the conduction system depends on the peculiarities of the heart structure at its congenital malformations rather than from changes in the structure and position of the parts of the conduction system, or the conduction system as a whole according to the types of congenital heart malformations. The mechanism of the left-sided position of the atrioventricular bundle (His bundle) in some congenital malformations of the heart is explained.     

Electron microscopy of the impulse conducting system op the sheep heart

Summary Electron micrographs of the conducting system of the sheep heart show it to be strictly cellular in nature. All protoplasmic components are restricted to areas defined by the individual plasma membranes of the cells. The individual cells are surrounded by a common interspace and groups of cells are separated from neighboring connective tissue by a common, longitudinal basement membrane. The extracytoplasmic interspace shows occasional enlargements, probably corresponding to the intracytoplasmic vacuoles visualized in the light microscope. The apposing plasma membranes, along which ephaptic thickenings may occur, and their interspace form the intercalated discs of the system.Myofibrils are few and are situated preferentially immediately beneath the plasma membrane. Chains of myofibrils, interrupted at the intercalated discs, appear to course through the whole tissue. In some myofibrils the pattern of long periods may be interrupted by a small-period pattern for several sarcomeres.The cytoplasmic matrix consists mainly of fine filaments of unknown composition. The relatively scarce mitochondria are found near the nucleus, myofibrils and cell surface. The endoplasmic reticulum is poorly developed and its arrangement is a comparatively loose one.The above results and their physiologic consequences are discussed, particularly with regard to the core conduction theory in conducting tissue.This study was aided, in part, by grant number H-3493, from the National Heart Institute of the National Institutes of Health, Department of Health, Education and Welfare, Bethesda, Maryland.     

Morphology of the principal divisions of heart conducting system of rats]

Light optic and electron microscopic investigation of the sinuauricular node node (spu), atrioventricular node (pzhu) and bundle of His (pzhp) has been carried out in 23 hearts of intact non-inbred male rats. Original techniques of oriented embedding of elements of the conductive system for their electron microscopic identification have been suggested. A morphological classification of specialized cardiac myocytes has been worked out basing on differences in their form and size, number of myofibrils and degree of their regulation. On its base three type of specialized myofibrils have been revealed in the conductive system. Topography of these cells has been described within spu, pzhu and pzhp. The suggested ultrastructural classification of specialized cardiac myocytes is compared with the data obtained for the cardiac conductive system in other types of mammals.     

On the impulse conducting system of the monkey heart (Macaca mulatta)

Summary The atrio-ventricular (A-V) node of the monkey heart is located in the focus of converging atrial muscle. Three main atrial muscle strands, coming from the atrio-ventricular ring, the dorsal wall of the atria, and the ventral part of the atrial septum, converge in the nodal region where they overlap and are interconnected. The junctional type of fibers establishing interconnection between the atrial muscle and the nodal tissue are not strictly localized at the periphery of the node, but may be traced further, along the A-V ring and coronary sinus. The A-V node consists of a loose peripheral and a compact distal part. In the former, typical nodal fibers were found, while the compact part shows an important individual variation in structure and cell-types. In some monkey hearts, the nodal fibers gradually become broader bundle fibers, while in other specimens the junctional fibers surround the compact part and than penetrate the nodal-His (N-H) region. These junctional fibers become nodal fibers or are in terminal contact with large clear cells up to 50 in diameter. Clear cells of various diameters are often intercalated between the cell rows of the nodal and His-bundle fibers and may form a distinct cellular gate between the node and the His-bundle.This study was conducted in part in the Department of Histology and Embryology of the Medical University in Budapest.     

Vascularization and development of the cytoarchitecture in the human neocortical rudiment

The development of cytoarchitectonics of the brain rudiments in mammals is accompanied by the formation of an intracerebral vascular network. The relationship between these two processes is insufficiently clear. We studied the development of blood vessels and cytoarchitectonics in the neocortical rudiment of 6- to 13-week old human embryos. The light and electron microscopy methods were used, as well as histochemical visualization of NADPH-diaphorase in the vessel cells. The endothelium proliferation was evaluated using antibodies to proliferating cell nuclear antigen. Starting from week 8 of development, the tangentially oriented vessels formed a intraneural network in the ventricular zone of the rudiment, which appears to restrict the motility of neuroepithelial cells. The basal membrane was initially absent, and the neuroepithelial cells were in direct contact with the endothelial cells. During week 9 of development, the tangentially oriented vessels appeared in the intermediate zone. Formations similar to glial legs with short regions of the basal membrane adjoined the walls of inter- and intraneural vessels (note that, according to the published data, glial fibrillary acidic protein is not yet visualized at this stage). Angioarchitectonics depended little on the cell population density in different zones of the rudiment; specifically, the cortical plate did not contain tangentially oriented vessels until week 12-13 of development. The data we obtained suggest that the blood vessels fulfill a special morphogenetic function in the developing neocortex.     

The fine structure of the conducting system of the monkey heart (Macaca mulatta)

Summary In the sino-atrial (S-A) node of the monkey heart two types of muscle cells occur: 1. typical nodal cells which are the predominant cells and form the nodal fibers. 2. Intercalated clear cells with various diameters (4 to 12 m) and containing poorly developed myofibrils, rich in glycogen and demonstrating poor staining properties. These latter cells are dispersed, few in number, and never form discrete fibers of themselves, but are intercalated between the cell rows of the typical nodal fibers. Such intercalated clear cells become more numerous at the periphery of the node. Interconnection between the S-A node and the conventional atrial muscle is established by a progressive transformation of nodal fibers into atrial fibers producing an intermediate (or junctional) type of fiber at the nodal periphery. However, in addition, few nodal fibers make direct contact with the atrial cardiocytes. Our light and EM studies have failed to prove the existence of truly specialized internodal pathways. Nevertheless intercalated clear cells, nodal-like cells, junctional or intermediate type of cells are relatively frequent in valvular regions (Thebesian, Eustachian, A-V, fossa ovalis) and less frequent in other regions of the atrial wall.This study was conducted in part in the Department of Histology and Embryology of the Medical University in Budapest.     

Proteoglycan and collagen expression during human air conducting system development

The lung is formed from a bud that grows and divides in a dichotomous way. A bud is a new growth center which is determined by epithelial-mesenchymal interactions where proteins of the extracellular matrix (ECM) might be involved. To understand this protein participation during human lung development, we examined the expression and distribution of proteoglycans in relation to the different types of collagens during the period in which the air conducting system is installed. Using light microscopy and immunohistochemistry we evaluate the expression of collagens (I, III and VI) and proteoglycans (decorin, biglycan and lumican) between 8 to 10 weeks post fertilization and 11 to 14 weeks of gestational age of human embryo and fetus lungs. We show that decorin, lumican and all the collagen types investigated were expressed at the epithelium-mesenchymal interface, forming a sleeve around the bronchiolar ducts. In addition, biglycan was expressed in both the endothelial cells and the smooth muscle of the blood vessels. Thus, the similar distribution pattern of collagen and proteoglycans in the early developmental stages of the human lung may be closely related to the process of dichotomous division of the bronchial tree. This study provides a new insight concerning the participation of collagens and proteoglycans in the epithelial-mesenchymal interface during the period in which the air conducting system is installed in the human fetal lung.Key words: human fetal lung, collagens, proteoglycans, extracellular matrix.     

Vascularization of the thymus in the duck

The arrangement and the blood of Thymus lobes were shown by intra-vasal injection of Indian ink or Neoprene Latex. The origin and the distribution of the arteries were studied within thymic lobe and until the final branches represented by endolobulare capillaries. These branches represent the origin of the vein of the thymic lobe.