Herzstudie II. Mitteilung: Histologische, histochemische und experimentelle Untersuchungen am Atrioventrikularsystem von Huf- und Nagetieren

Differentiation of the atrioventricular conducting system of the heart

The structure and function of the atrioventricular conducting system of the heart, and its relationship to the myocardium, are examined from a developmental point of view. On the basis of information derived from electron micrographic, electrophysiologic, and developmental studies of heart tissue, it is concluded that: (1) The idea of the syncytial nature of the heart lacks a sound anatomic basis. (2) Cytodifferentiation during embryonic cardiogenesis results in the development of at least 2 distinct populations of cells: those comprising the bulk of the myocardium and a second type, the specialized cells of the conductive tissue, which differs in histology, biochemistry, and physiology. (3) The common view of the myocardium as a spontaneously active tissue may require revision, since several lines of evidence appear to indicate that myocardial cells are quiescent until stimulated by an extrinsic source. Under normal circumstances, this stimulus source is the conductive tissue.

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.

Electrical activity of sinoatrial node cells of the rabbit surviving a long exposure to cold Tyrode's solution

The right atrium including the sinoatrial node was excised from the rabbit heart, immersed in Tyrode's solution, and kept at 0-3 degrees C for several days. The tissue then was warmed to 36-37 degrees C in well oxygenated Tyrode's solution. Transmembrane potentials from cells in the sinoatrial node region and the right atrium were recorded with microelectrodes. After 3 days of storage, the maximum diastolic potential of cells in the sinoatrial node region decreased, but the configuration of the action potential was identical to that of the pacemaker pacemaker potential in the fresh preparation. After 5-7 days of storage, the sinoatrial node tissues in some preparations showed well preserved membrane potentials and pacemaker activity, while in others, the cells were electrically quiescent, or showed subthreshold oscillatory potentials of low amplitude. Transmembrane potentials could not be recorded from the right atrial tissue after storage for this period. Sinoatrial node action potentials with normal configuration were recorded from preparations stored for longer than 10 days. The sinoatrial cells in these preparations responded well to norepinephrine and acetylcholine, indicating that the reactivity of receptors was well preserved. The results provide electrophysiological evidence that cells in the sinoatrial node region can withstand long exposure to cold and retain their sensitivity to neuromediator action, but atrial myocardial cells cannot.

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.