Morphological study of the atrioventricular conduction system and Purkinje fibers in yak.

We studied the morphology of the atrioventricular conduction system (AVCS) and Purkinje fibers of the yak. Light and transmission electron microscopy were used to study the histological features of AVCS. The distributional characteristics of the His-bundle, the left bundle branch (LBB), right bundle branch (RBB), and Purkinje fiber network of yak hearts were examined using gross dissection, ink injection, and ABS casting. The results showed that the atrioventricular node (AVN) of yak located in the right side of interatrial septum and had a flattened ovoid shape. The AVN of yak is composed of the slender, interweaving cells formed almost entirely of the transitional cells (T-cells). The His-bundle extended from the AVN, and split into left LBB and RBB at the crest of the interventricular septum. The LBB descended along the left side of interventricular septum. At approximately the upper 1/3 of the interventricular septum, the LBB typically divided into three branches. The RBB ran under the endocardium of the right side of interventricular septum, and extended to the base of septal papillary muscle, passed into the moderator band, crossed the right ventricular cavity to reach the base of anterior papillary muscle, and divided into four fascicles under the subendocardial layer. The Purkinje fibers in the ventricle formed a complex spatial network. The distributional and cellular component characteristics of the AVCS and Purkinje fibers ensured normal cardiac function.

Significant damage of the conduction system during cardioplegic arrest is due to necrosis not apoptosis.

OBJECTIVES: Ventricular conduction disturbances following cardioplegic arrest remains a serious, yet unsolved problem. In the present study we examined whether myocardial conduction cells (MCC, Purkinje fibers) are more vulnerable to ischemia/reperfusion injury than working myocardial cells and whether the damage is due to necrosis or apoptosis. METHODS: Mini-pigs were subjected to 60 min of crystalloid (St Thomas; n = 15 group I) or blood (Buckberg; n = 6 group II) cardioplegic arrest followed by 3 h of reperfusion. Animals not subjected to either procedures served as controls (n = 5). Ventricular myocardial specimens were investigated by hematoxylin and eosin (HE) and periodic acid Schiff (PAS) staining and immunohistochemical labeling of apoptosis-associated proteins (Bax, Bcl-2, Caspase-3). DNA-breaks were visualized by in situ end labeling (terminal deoxynucleotidyl transferase dUTP-biotin nick-end labeling, TUNEL). Electron microscopy confirmed apoptosis or necrosis. RESULTS: MCC of control hearts intrinsically expressed Bax, Bcl-2, and Caspase-3 without signs of either apoptotic or necrotic damage. Subendocardial Purkinje fibers of groups I and II hearts exhibited focal damage, with reduced labeling of apoptosis-associated proteins, glycogen loss, karyopycnosis and increased eosinophilia (15/21 hearts). The majority of damaged MCC displayed nuclear TUNEL-positivity (2.8+/-2.5% of MCC), whereas the average TUNEL-rate of the adjacent working myocardium was low (<0.1%). Electron microscopy demonstrated ischemic changes in MCC consistent with cellular necrosis. CONCLUSIONS: Ischemia/reperfusion injury due to cardioplegic arrest inflicts significant damage on subendocardial MCC, but not on working myocardium. Ultrastructural and light-microscopic findings are consistent with coagulation necrosis, rather than apoptosis.

[Changes of the heart conduction system after exposure to fluorouracil]. / Izmeneniia provodiashchei sistemy serdtsa pod vliianiem ftoruratsila.

Using 20 male rats the electron microscopic study of conducting system of the heart was performed to assess the effect of fluorouracil--an antineoplastic drug belonging to antimetabolite group. A daily dose of 15 mg/kg of fluorouracil was injected intraperitoneally for 5 days; three courses of injections with the intervals of three weeks were performed. Toxic effect of fluorouracil is demonstrated after the first course of injections and is revealed as a predominant injury of pacemaker cells in sinoatrial and atrioventricular nodes. Latent pacemaker myocytes and Purkinje fibers undergo "calcium injury" during the second and the third courses of fluorouracil injections. The irreversible damage of contractile and specialized myocytes results in fibrosis which develops predominantly in the areas of atrioventricular bundle and its branches.

Restrictive cardiomyopathy due to desmin accumulation in a family with evidence of autosomal dominant inheritance.

OBJECTIVE: A familial case of restrictive cardiomyopathy due to desmin accumulation characterized by severe disturbances of cardiac conduction is described. BACKGROUND: Desmin is an intermediate filament normally present in the myocardium, particularly in the Purkinje fibres, in the skeletal and in the smooth muscle. METHODS: Resting electrocardiogram, 2-dimensional and Doppler echocardiogram, cardiac catheterization, electrophysiological study have been performed in all siblings. Informed consent for endomyocardial biopsy was obtained only in one patient. RESULTS: The mother showed bilateral pes cavus and complained of episodes of vertigo at the age of 36 years. At that time she was submitted to electrophysiological study and to permanent pacing. After 15 years of good health conditions, she developed heart failure and underwent cardiac transplantation. A 21 year old son had a syncope; his ECG was similar to that of his mother; a permanent pacemaker was implanted and a diagnosis of restrictive cardiomyopathy with desmin accumulation was confirmed at histopathology study. Afterwards, another 24 year old sib had a syncope with head trauma: ECG showed right atrial enlargement, left bundle branch block. After electrophysiological study, he started antiarrhythmic therapy. This patient showed bilateral pes cavus. CONCLUSIONS: The early manifestation of desmin accumulation may be intraventricular conduction disorders that can be often controlled by pacemaker implantation. Clinical symptoms of heart failure may be absent for a long period of time. Pedigree analysis is most consistent of autosomal dominant inheritance.

Immunohistochemical delineation of the conduction system. II: The atrioventricular node and Purkinje fibers.

Using an antibody that reacts specifically with the myocytes of the conduction system of the bovine heart, we have studied the atrioventricular node and the spatial distribution of the Purkinje fibers in the bovine heart. This study was complemented by studying the distribution of the gap junction protein connexin43 in these areas in the bovine heart and in the human heart. The large Purkinje fibers in the bovine heart are arranged in a two-dimensional network underneath the endocardium. At discrete sites, these fibers branch to the Purkinje fibers situated between the muscle bundles of the ventricular mass. These intramural Purkinje fibers are arranged in sheets that form a complex three-dimensional network of lamellas. Contacts with the ventricular myocytes are found throughout the myocardial wall, with the exception of a subepicardial layer of 2-mm thickness, ie, 10% to 15% of the wall thickness. The spatial arrangement of the Purkinje fibers correlates well with data on electrophysiology. Connexin43 was not detected in the myocytes of the atrioventricular node, whereas in the Purkinje fibers of the atrioventricular bundle and of the bundle branches, abundant expression of connexin43 was found in both humans and cows. In the bovine Purkinje fibers, a remarkable subcellular distribution of connexin43 is found: it occupies the entire plasma membrane facing other Purkinje cells but not that facing the surrounding connective tissue. The structural differences in architecture of the ventricular conduction system in humans and cows seems not to result in substantial differences in conduction velocities. However, the Purkinje fiber network in the bovine heart may explain the efficient ventricular excitation, as reflected by the relatively short QRS complex compared with that in the human heart, where intramural Purkinje fibers are not found.

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 mechanism of rectification of iK1 in canine Purkinje myocytes.

We have characterized the inward rectifying background potassium current, iK1, of canine cardiac Purkinje myocytes in terms of its reversal potential, voltage activation curve, and "steady-state" current-voltage relation. The latter parameter was defined from the difference current between holding currents in the presence and absence of 20 mM cesium. Our data suggest that iK1 rectification does not arise exclusively from voltage-dependent gating or exclusively from voltage-dependent blockade by internal magnesium ions. The voltage activation curve constructed from tail currents fit to a Boltzmann two-state model predicts less outward current than is actually observed. The magnesium-dependent rectification due to channel blockade is too fast to account for the time-dependent gating of iK1 that gives rise to the tail currents. We propose a new model of rectification that assumes that magnesium blockade of the channel occurs simultaneously with voltage-dependent gating. The new model incorporates the kinetic schema elaborated by Matsuda, H. (1988. J. Physiol. 397:237-258) to explain the appearance of subconducting states of the iK1 channel in the presence of blocking ions. That schema suggested that iK1 channels were composed of three parallel pores, each of which could be blocked independently. In our model we considered the consequences of partial blockade of the channel. If the channels are partially blocked at potentials where normally they are mostly gated closed, and if the partially blocked channels cannot close, then blockade will have the paradoxical result of enhancing the current carried by iK1.

Immunohistochemical identification of Purkinje fibers and transitional cells in a terminal portion of the impulse-conducting system of porcine heart.

The ultrastructure of porcine ventricular tissue was studied by electron microscopy and immunocytochemical techniques. Electron-dense specific granules were found in both Purkinje fibers and transitional cells in the ventricular walls, and were positively stained by the immunogold staining method using an antiserum against atrial natriuretic polypeptide (ANP). This suggests that both the Purkinje fibers and transitional cells display the same specific granules as atrial cardiocytes containing ANP. These results demonstrate that Purkinje fibers and two types of transitional cells, in addition to the ordinary ventricular cardiocytes, can be identified in porcine ventricular wall tissue.

Ischemic injury to the conducting system of the heart. Involvement of myocardial lysosomes.

The conducting system was studied in an in situ perfused swine heart preparation with reduced coronary flow (ischemia) using perfusate containing high and low levels of glucose (26.6 versus 8.6mM) with and without insulin. Coronary flow was maintained at normal levels for 60 minutes in control hearts. In ischemic hearts flow was reduced to about 50 percent of control levels for 30 minutes. Ultrastructural studies documented only subtle modifications of Purkinje fibers in ischemic hearts. Glycogen depletion and disruption of cell junctions were observed in some fibers. One consistent finding was the activation of the lysosomal system. The outer membranes of primary lysosomes appeared herniated and in some cases disrupted, and small vesicles containing hydrolytic enzymes were seen in association with the Golgi apparatus and larger primary lysosomes. Specimens prepared for the demonstration of acid phosphatase indicated a redistribution of hydrolytic enzymes in Purkinje fibers with a depostion of acid hydrolases in smaller lysosomal vesicles, the transverse and side-to-side junctions between cells, and occasionally in the sarcoplasmic reticulum. Enriched perfusate containing high levels of glucose with insulin appeared to have no therapeutic effects in terms of the structure of the Purkinje fibers. The results suggest that alterations in the lysosomal system may be one of the earliest structural changes which occur in oxygen-deficient hearts.