Herzstudie I. Mitteilung: Histochemische Untersuchung der Purkinjefasern von S�ugern

The ultrastructural effects of global ischaemia on Purkinje fibres compared with working myocardium: a qualitative and morphometric investigation on the canine heart

During open heart surgery, reperfusion-induced arrhythmias arising after short periods of ischaemia may originate from subendocardial Purkinje fibres. We investigated the ultrastructure of these fibres during 30 min of global ischaemia at 25 degrees C. The effects both with myocardial protection (HTK cardioplegia) and without it (pure ischaemia) were compared qualitatively and morphometrically. After 30 min pure ischaemia overcontraction of sarcomeres, hypercontraction and contraction bands, together with considerable changes in organelles, predominate over cellular oedema. In Purkinje fibres, both cellular and mitochondrial swelling were significantly increased within this 30-min time period from the onset of pure ischaemia. In contrast, following HTK cardioplegia and 30 min ischaemia, cellular and mitochondrial swelling remain moderate and over-contractions are almost entirely lacking. This means that despite remarkable differences between pure ischaemia and HTK cardioplegia in the degree of protection attained it is clear that, compared with the working myocardium, subendocardial Purkinje fibres do not display a higher resistance to early global ischaemia. Further investigations of this sensitivity of Purkinje fibres to global ischaemia and certain drugs may bring about new insights into myocardial protection and pharmacotherapy of arrhythmias.

The conduction system in Pompe's disease

We report our findings in the microscopic examination of the conduction system in four infants with glycogen storage disease, one of whom had adequate electrophysiologic studies. The electrophysiologic studies in the latter case showed P-A and A-H intervals at the lower limits of normal, but the H-V interval was just above the normal mean. This suggests that the rapid conduction was not localized in the anatomic counterpart of the H-V interval. The short P-R interval in the ECG may be related to the enlargement of cells, which may in turn be related to increased glycogen content. The relationship of glycogen per se to the speed of conduction is unknown. We found that the summit of the ventricular septum bulged, probably because of the generally increased cell size, and that the topography of the atrioventricular conducting system was different from normal. This is possibly related both to an increase in the cell sizes of the specialized conducting tissue itself and to deforming effects of this bulging summit of the ventricular septum. New microscopic details of the components of the conducting system are described in these cases.

Enzyme histochemical studies on the conducting system of the human heart

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.

Enzyme histochemical studies on the Purkinje fibers of the atrioventricular system of the bovine and porcine hearts

In this communication the results of applying various histochemical semipermeable membrane techniques to the localization of several enzymes in bovine and porcine heart are presented. The Purkinje fibers of the atrioventricular conducting system of the bovine heart differ from the myocardium proper in containing a greater activity of the glycolytic and gluconeogenetic enzymes--lactate dehydrogenase, glyceraldehyde-phosphate dehydrogenase, hexokinase, glucosephosphate isomerase and phosphoglucomutase, and less activity of the aerobic enzymes--NADH: nitroBT oxidoreductase and isocitrate dehydrogenase (NADP+). The metabolic reactions obtained with Purkinje fibers of the porcine heart are less pronounced. These histochemical findings are in accordance with the impression that Purkinje fibers, compared with the common myocardial fibers, have a higher rate of anaerobic metabolism and a lower rate of aerobic metabolism. The activity of the NADPH regenerating enzymes glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase (decarboxylating), and the activity of acid hydrolases such as non-specific esterase and acid phosphatase is higher in the Purkinje fibers of both the bovine and porcine heart.

Purkinje fibre glycogen. A morphologic and biochemical study of glycogen particles isolated from the cow conducting system

Glycogen from the cow conducting system was extracted by crude and mild methods. For comparison similar extractions were also performed on cow ordinary ventricular tissue. Glycogen particles from the conducting system, isolated by a mild method, were characterized by a low molecular weight (3-5 X 10(6)) and small dimensions (average diameter about 30 nm). 3.5-7% protein was firmly bound to the glycogen. The glycogen, based on spectrophotometric analysis, appeared to be in a native state. Glycogen as a polysaccharide-protein complex can thus be obtained from the cow conducting system and is proposed to be useful for analysis of the structure and function of glycogen in the conducting system.

Hypertrophy versus hyperplasia

Although all tissues and organs of the body are normally subject to the growth-regulating influences of functional demands, some are potentially capable of unlimited growth while others are not. This depends on whether hyperplasia of their functional units ceases prior to maturity or can continue throughout life. In the former case, further growth is limited by the extent to which hypertrophy can enhance physiological efficiency. Some of the body's most vitally essential organs (heart, brain, kidney, lung) lack the ability to make additional structural units in the adult and are therefore handicapped in compensating for the depreciations of advancing age. Theoretically, at least, other organs (glands, renewing tissues) possess unlimited powers of regeneration because they never lose the capacity (latent or expressed) for hyperplasia. There is a strategy in the way growth mechanisms have evolved. It may be significant that the so-called "hypertrophic" organs lose the capability for hyperplasia, because not to do so might jeopardize their growth regulation. If size is determined by functional demands, then the latter must not operate continuously lest growth go on without interruption and lead to overproduction of functional units. Only renewing tissues can tolerate perpetual growth because they get rid of excess structures as fast as they are formed. Endocrine and exocrine glands are in most cases known to function discontinuously and are thus not in danger of being overstimulated. The heart, lungs, and kidneys (and brain?), however, must work incessantly. Were their functional units capable of hyperplasia and at the same time subject to control by functional demand, then overgrowth would seem to be inevitable. By giving up the potential for hyperplasia in favor of the necessity for constant function, these organs have adopted a strategy that enables them to become hypertrophic to a limited extent while doing their jobs efficiently. It is a curious fact that the unrestricted proliferation of biological structures cannot occur at all levels of organization. The counterpart of cancer, which is a cellular phenomenon, does not exist among molecules or cytoplasmic organelles, nor is it known to occur at the histological level of organization. Even in organs made up of histological units of function and having the potential for unlimited hyperplasia (for example, liver, exocrine glands, thyroid, ovary), the population of functional units never exceeds the number needed to fulfil the physiological requirements of the body. Above and below the level of the cell, therefore, structures are not permitted to escape the constraints of functional demands which control their production. The fact that cells can occasionally do so when they become neoplastic may reveal as much as it conceals about the problem of growth regulation.