Enzyme histochemical studies on the conducting system of the human heart

Abstract

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, beta-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.

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

“…The abundance of this enzyme in the prenatal compared to the postnatal heart has also been established biochemically (Henderson, 1977). In comparing our results with reports that claim that the adult conduction system is rich in AChE activity (Elias et al, 1980) it has to be kept in mind that we only describe AChE activity in myocytes. It is not always clear whether the rich nerve supply of the definitive conduction system (James and Spence, 1966;Moravic and Moravic, 1984) is taken into account.…”

Histochemical studies on the conduction system of diabetic rat hearts.

“…4). that the oxygen uptake and the activity of succinate dehydrogenase were much lower in the conduction system whereas the glycogen concentration was higher than in the working myocardium (SNIJDER and MEIJER, 1970;MEIJER and DEVRIES, 1978;ELIAS et al, 1980ELIAS et al, , 1982TsuYUGUCHI et al, 1980;THERY et al, 1985). These data suggest that the conduction system may depend more on glycolysis for energy supply than does the working myocardium, and that it is more resistant to anoxic damages.…”

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

“…The same has also been described for the conducting system in man (Thery eta]., 1985). Elias et al (1980), however, found no significant differences in LDH activity between the different types of human cardiac cells.…”

“…Earlier studies carried out by means of qualitative histochemistry also led to confusing results. Thus, the specialized muscle cells of the conducting system were found to manifest lower succinate dehydrogenase activity in comparison with the other cardiac muscle cells (Schiebler, 1962;Schiebler & D6rr, 1963;Otsuka eta]., I967; Snijder & Meijer, 1970;Elias et al, 1980). From this it was concluded that the conducting system is provided with only weak capacity for oxidative energy metabolism, but with a higher activity of the enzymes of anaerobic glycolysis.…”