Enzyme histochemical studies on the conducting system of the human heart

Microquantitative determination of lactate dehydrogenase isoenzymes in the myocardium and the conducting system

A newly developed technique was used for the electrophoretic separation of lactate dehydrogenase (LDH) isoenzymes from lyophilized tissue samples in the nanogram range. In this study portions of 10-200 ng from the myocardium and the conducting system of cattle, sheep, pig and man were microdissected and analysed. In the heart tissues of cattle, sheep and pig, the isoforms LDH1, LDH2 and LDH3 were detected in species-specific varying amounts. In all these animals, the conducting system is marked by high LDH1 activity, which is present at a ratio of about 2:1 compared with the myocardium. The values in man, however, differ from these values, but this might be due to post-mortem changes. The findings are discussed with respect to possible aerobic-anaerobic functions.

The pentose phosphate pathway in skeletal muscle under patho-physiological conditions. A combined histochemical and biochemical study

Over the last 30 years, research into the neuromuscular apparatus, has expanded greatly. Multidisciplinary investigations have rapidly advanced our understanding both of diseases and of the basic neuromuscular mechanisms. The mode of pathological reaction of the neuromuscular apparatus is now quite well understood. The most notable aspect of the reaction of the injured neuromuscular apparatus is the remarkably stereotyped character of the resulting pathological changes as demonstrated by a wide variety of harmful causes, producing surprisingly similar effects. The findings of our combined histochemical and biochemical investigations presented in this monograph, are in complete harmony with the stereotyped character of the pathological changes. For example, it is particularly striking that many affected muscle fibres of patients with muscular dystrophies, congenital myopathies, inflammatory myopathies, metabolic myopathies, endocrine myopathies, or with diseases of the lower motor neuron, display an enhanced activity of both oxidative enzymes of the pentose phosphate pathway. Likewise, we found that experimental animals with disordered skeletal muscles, provoked by different types of agents or treatments, reveal the same marked rise in activity of GPDH and PGDH in the muscle fibres, with a positive correlation between the activity of both enzymes. Other findings of our investigations point to a positive correlation between the activity of GPDH and PGDH on the one hand and that of the non-oxidative enzymes of the pentose phosphate pathway, the enzymes TA, TK, RPI and RPE on the other hand. The rise in activity of PGDH and, in particular, of GPDH is regulated by two different mechanisms. The first represents a rapid control mechanism based on the stimulation of both oxidative enzymes of the pentose phosphate pathway by NADP+ and on their inhibition by NADPH. The other mechanism represents a long-term effect directed at the synthesis of the enzymes. It is this type of mechanism which is responsible for the rise in activity of GPDH and PGDH we observed. The findings obtained with the applied enzyme histochemical techniques clearly demonstrated that the rise in activity of both enzymes is not homogeneously distributed in the disordered skeletal muscles of man and experimental animals. For that reason, in order to obtain reliable quantitative information about enzyme activities in the muscle fibres themselves, the application of biochemical assays on a micro-scale was indispensable. The biochemical assay of enzyme activities was performed on histologically and histochemically selected dissected muscle specimens.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholinesterase molecular forms in muscle and non-muscle cells of rat heart

Experiments were performed to determine the cellular associations of the molecular forms of acetylcholinesterase (AChE) in adult rat heart. For this purpose, a cardiac muscle and a non-muscle fraction were isolated from rat heart ventricles after perfusion with collagenase and hyaluronidase, extracts of these fractions were subjected to ultracentrifugation on linear density gradients of sucrose (5-20%), and fractions of these gradients were analyzed for AChE activity. The results show that only globular AChE molecular forms were present in isolated cardiac muscle cells. Globular AChE forms were also present in the non-muscle cells fraction but in different proportions. The proportions of globular AChE forms plus the high specific activity of choline acetyltransferase in the non-muscle cell fraction suggest that this fraction contains cholinergic nerve fragments. The results of this study also show that asymmetric AChE is released during the perfusion of heart with the digestive enzymes, which suggests that asymmetric AChE is bound to the extracellular matrix of heart.

Quantitative histochemistry of creatine kinase in rat myocardium and skeletal muscle

Creatine kinase (EC 2.7.3.2) activity was demonstrated in rat myocardium using a polyvinyl alcohol-containing incubation medium and auxiliary enzymes. The activity was quantified by microdensitometry using both endpoint measurements and kinetic measurements. Control reactions were performed in the absence of creatine phosphate and ADP. The linear regression lines of the absorbances of reduced Nitro BT at the isobestic wavelength (585 nm) on incubation time were highly significant for both endpoint and kinetic measurements. The activity obtained from endpoint measurements was about 40% lower. This was caused by loss of the formazan reaction product from the tissue sections when the incubation medium was removed at the end of the reaction. The relationship between creatine kinase activity (test minus control reaction) and section thickness was not linear for either myocardium or skeletal muscle; control reactions, however, showed linear relationships with section thickness for both tissues. Limited penetration of auxiliary enzymes into the sections may be responsible for this disporportionality. Therefore, care should be taken in the interpretation of quantitative data obtained with different tissues. In conclusion, multi-step enzyme reactions can be used for quantitative histochemical purposes provided it is taken into account that the reactivity is not proportional to section thickness.

Acetylcholinesterase in prenatal rat heart: a marker for the early development of the cardiac conductive tissue?

In rat embryos, acetylcholinesterase (AChE, EC 3.1.1.7) activity is present in a continuous sleeve of myocytes that extends from the myocardium that is adjacent to the atrioventricular endocardial cushions via the ventricular trabeculae to the outflow tract. No activity is found in the atrial roof, in the ventricular walls and in the interventricular septum except for its subendocardial surface. AChE-positive cells are first identified in 11-day rat embryos, while the prototypical distribution is best demonstrable in 13-day embryos. Part of the AChE-positive cell system is identifiable as a precursor of the adult conduction system by topographical criteria in 16-day fetuses and by morphological criteria in 20-day fetuses. At birth (2 days later), AChE activity has disappeared from the cardiac myocytes except for a ring of tissue at the atrial side of the atrioventricular junction. These findings suggest that the embryonic heart can be divided into an upstream myocardium that has no AChE activity and a downstream myocardium that is characterized by the presence of AChE. Furthermore they suggest that an acetylcholine-dependent mechanism may be responsible for the retardation of the depolarization wave in the downstream parts of the heart. Finally they show that the adult conduction system is formed by a transdifferentiation of part of a far more extensive embryonic precursor system.

Differentiation of the atrioventricular node, the atrioventricular bundle and the bundle branches in the bovine heart: an immunohistochemical and enzyme histochemical study

The previous observations of differences between different cardiac regions (ventricular myocardium, atrial myocardium, Purkinje fibre system) with respect to the maturation of the M-line region and the establishment of mature metabolic characteristics, have been extended. It was found that M-line maturation proceeds differently also between different regions of the conduction system. The M-line proteins, myomesin and MM-creatine kinase, were detected earlier, by means of immunohistochemistry, in the AV bundle and bundle branch cells than in the AV node cells. Also, a difference was observed in large foetuses. Striations in the AV node were less evident than in the AV bundle and the bundle branches in sections incubated with antibodies against myomesin as well as against MM-creatine kinase. Using enzyme histochemistry it was observed that the differences in metabolic properties between the AV node, the AV bundle and the bundle branches on the one hand, and the ordinary myocardium on the other, of adult hearts, are not established at the early stages. No clear difference in activity of succinate dehydrogenase was seen between the conduction tissues and the ordinary myocardium in the foetal hearts, while the conduction tissues showed a lower activity in the adult hearts. Furthermore, the pattern of activity of mitochondrial glycerol-3-phosphate dehydrogenase between the conduction tissues and the atrial and ventricular myocardium was quite different in early foetal stages compared with the adult stage.

The demonstration of close nerve-Purkinje fibre contacts in false tendons of sheep heart

An observation of intimate nerve-Purkinje fibre associations in false tendons of sheep heart is reported. Nerve bundles were observed in deep clefts of Purkinje fibres, in channels running between coupled Purkinje cells and embedded within Purkinje cells, as well as in the outer connective tissue sheath. Most nerve terminals in these areas were filled with small clear vesicles and a few large dense-cored vesicles. Only a few axons with many small dense-cored vesicles were observed. Intimate associations (separation, 60 to 90 nm) between the Purkinje cell and nerve varicosity were observed in the deep clefts. Similar close appositions were also present where nerves were embedded in Purkinje cells. In these cases the Purkinje cell enclosing the nerve bundle formed intercellular junctions with its own sarcolemma. Elaborate sarcolemmal folds with multi-vesicular bodies were also frequently observed near nerve bundles and varicosities. The identity of the transmitter is unknown although the nerves forming intimate associations with Purkinje cells have a morphology typical of cholinergic nerves.

Congenital "histiocytoid" cardiomyopathy: evidence suggesting a developmental disorder of the Purkinje cell system of the heart

The so-called "histiocytoid cardiomyopathy" is an unusual cardiac disorder of infancy and childhood, characterized by the presence of numerous foamy, lipid-containing cells between the endocardium and the striated myocardial cells of the left ventricle and the interventricular septum. The disease usually affects females, the clinical picture being dominated by severe disturbances of conduction. The original designations of the disorder stem from the morphological resemblance of the foamy cells to lipid-laden histiocytes. However, subsequent investigations have shown these cells to contain myofibrils interposed with Z lines. It has, therefore, been suspected that the leading cell population might be related to the myocardium. Using a histochemical method for the demonstration of cholinesterase activity in the foamy cells, we present evidence that "histiocytoid" cardiomyopathy may in fact correspond to a maldevelopment of the Purkinje cell system of the heart.

Myocardial cell heterogeneity in the human heart with respect to myosin ATPase activity

The PH sensitivity of the Ca2+-activated myosin ATPase in atrial, ventricular and conduction tissue of human hearts has been established. Heterogeneity with respect to ATPase activity is shown not only to exist between the atrial, the ventricular myocardium and the conduction system but also within both the ordinary atrial and ventricular myocardium and within the conduction system. These observations are related to the polymorphism of the myosin molecule and suggest that fibre types with different contractile properties co-exist in the human heart.