Cardiac arrhythmogenesis and the gap junction.
Explore the source record for details and available documents.
Amino Acid Sequence↗
Biomedical subjects
N S Peters
Publications and source records attributed to N S Peters.
Upregulation of connexin43 gap junctions during early stages of human coronary atherosclerosis.
Interactions between cells form the framework for understanding the pathogenesis of atherosclerosis, but little information is available on the role of direct intercellular communication via gap junctions in this process. To investigate gap junction expression in the pathogenesis of human atherosclerosis, lesions representing different stages of the disease were obtained from coronary arteries of hearts removed from patients undergoing cardiac transplantation. Twelve hearts, each providing 1 to 3 segments of artery, were used in the study. Sections were examined by confocal laser scanning microscopy after immunofluorescent labeling with a specific antibody against connexin43, the major gap-junctional protein of smooth muscle cells, to permit high-definition visualization of immunolabeled gap junctions through the depth of the specimen. Double labeling using anti-connexin43 and cell type-specific antibodies demonstrated colocalization of gap junctions with smooth muscle cells but not with macrophages, a relationship confirmed by electron microscopy. Regions of intimal thickening and early atheromatous lesions showed markedly increased expression of connexin43 gap junctions between intimal smooth muscle cells compared with the undiseased vessels. This increase in gap junctions was most marked in regions of intimal thickening, semiquantitative analysis of the confocal digital images revealing a > 10-fold increase compared with the undiseased vessel. The quantity of labeled gap junctions in early atheromatous lesions, although higher than that of the undiseased vessel, was lower than that of intimal thickenings, and this trend toward reduced levels of gap junction immunolabeling with lesion progression continued, the value observed in the most advanced atheromatous lesions being lower than that of the undiseased vessel. As the quantity of gap junctions declined, their distribution became more patchy and the sizes of individual junctions larger. The results suggest that enhanced expression of gap junctions between smooth muscle cells may play a role in maintaining the synthetic phenotype during early growth of the atherosclerotic plaque.
Aged↗
The Wolff-Parkinson-White syndrome: the cellular substrate for conduction in the accessory atrioventricular pathway.
The longstanding quest for the anatomical basis of the Wolff-Parkinson-White syndrome has left many unanswered questions. The ultrastructural morphology of the myocytes comprising accessory atrioventricular pathways, which are capable of rapid and variable conduction, is central to understanding the development and behaviour of this congenital anomaly, but remains unknown. Examination of three surgically resected pathways was performed to determine their underlying cellular morphology and the pattern of intercellular coupling, by correlative light microscopy, electron microscopy and confocal scanning laser microscopy combined with immunohistochemical localization of the cardiac gap-junctional protein, connexin43. Two left-sided pathways were composed of myocardium of 'normal working ventricular' type. The right-sided pathway was composed almost entirely of highly abnormal myocytes characterized by aberrant myofibril organisation, with a lack of A-band material and abnormal mitochondria, but normal intact intercalated disks no different from those seen in left-sided pathways. The gap junctions of all pathways were composed of connexin43 distributed as in ventricular myocardium, and not as found in atrial or atrioventricular nodal tissues. While myocytes of abnormal structure were present in one of the accessory atrioventricular pathways examined, all pathways had morphologically normal gap junctions, the structures responsible for efficient intercellular coupling, with a pattern of distribution suggestive of working ventricular myocardium.
Adolescent↗
Spatiotemporal relation between gap junctions and fascia adherens junctions during postnatal development of human ventricular myocardium.
BACKGROUND: The growing postnatal human heart maintains electromechanical function while undergoing substantial changes of cellular topology and myocardial architecture. The capacity for growth and remodeling of ventricular myocardium in adaptation to the hemodynamic changes of early infancy later declines. This decline is associated with changes in electromechanical properties of the myocardium, which suggest that the electrical and mechanical interactions between the myocytes may change in an age-dependent manner. Thus, reduction in the capacity for myocardial growth and adaptability may relate to age-dependent alterations in the patterns of the intercellular junctions that mediate electrical and mechanical coupling. We therefore examined the hypotheses that (1) age-dependent changes in the distribution patterns of gap junctions and fasciae adherentes, the intercellular junctions responsible, respectively, for electrical and mechanical coupling, accompany postnatal development in the human heart and that (2) such changes continue into the first few years of childhood. Further, the spatial relation between the two types of junction, for which a close association has been hypothesized as necessary, was explored. METHODS AND RESULTS: Ventricular myocardial gap-junction distribution was investigated in 23 pediatric surgical patients (4 weeks to 15 years old) by quantitative immunohistochemical localization of the principal cardiac gap-junctional protein, connexin43, using confocal microscopy. Immunolocalization of fascia adherens junctions by labeling N-cadherin, and correlative immunogold and standard electron microscopy, were performed in parallel. In the neonate, connexin43 gap junctions have a punctate distribution over the entire surface of the ventricular myocytes. With advancing age, gap junctions become progressively confined to the transverse terminals of the cell, ie, toward the distribution within the intercalated disk characteristic of the adult ventricle. The transversely arrayed proportion of gap-junctional label showed a linear increase with age (R = .88, P < .001), reaching the adult pattern at about 6 years, and the fascia adherens junctions showed a similar progression. Electron microscopy confirmed the changing pattern of junctional contacts and demonstrated that initially gap junctions and adhering junctions are frequently not closely adjacent but become increasingly so with maturation of the intercalated disk. CONCLUSIONS: Changes in the spatiotemporal patterns of the intercellular junctions responsible for electrical and mechanical coupling are closely coordinated in postnatal human ventricular myocardium and continue to about 6 years of age. Over this period there is a close and increasing association between the gap junctions and fascia adherens junctions. These changes in the distribution of intercellular electrical and adhering junctions may parallel the changing functional requirements of the ventricle, from a distribution that facilitates the remodeling necessitated by rapid growth and changing hemodynamics to that of the relatively stable and rapidly conducting adult myocardium. These age-related changes may also diminish the ability for appropriate myocardial remodeling in response to physiological, pathological, or surgical hemodynamic alterations.
Adolescent↗
Intercellular junctions and the application of microscopical techniques: the cardiac gap junction as a case model.
Intercellular junctions are fundamental to the interactions between cells. By means of these junctions, the activities of the individual cells that make up tissues are co-ordinated, enabling each tissue system to function as an integrated whole. In this review, the work of the authors on one specific type of junction--the cardiac gap junction--is presented as a case model to illustrate how the application of a range of microscopical methods, as part of a multidisciplinary approach, can help extend our understanding of cell junctions and their functions. In the heart, gap junctions form the low-resistance pathways for rapid impulse conduction and propagation, enabling synchronous stimulation of myocyte contraction. Gap junctions also form pathways for direct intercellular communication, a function of particular importance for morphogenetic signalling during development. The work discussed demonstrates some of the applications of techniques in electron microscopy, immunocytochemistry and confocal scanning laser microscopy to the understanding of the structural basis of the function of gap junctions in the normal adult heart, the developing heart and the diseased heart. Freeze-fracture electron microscopy of heart tissue prepared by rapid freezing techniques, in which excision-related structural damage to the cells is minimized or avoided, makes it possible to deduce the structure of the functioning gap junction in vivo. Gap junctions in hearts that are beating normally in the living animal until the very instant of freezing consist of connexons (transmembrane channels) organized in a quasi-crystalline arrangement, not a 'random' arrangement as proposed in the original hypothesis on the structural correlates of gap junction function. Alterations in connexon arrangement occur in response to ischaemia and hypoxia, though the relationship of these to gap-junctional permeability is indirect. To obtain probes for mapping the distribution of gap junctions in cardiac tissue, polyclonal antisera to synthetic peptides matching portions of the sequence of connexin43, the major gap-junctional protein reported in the heart, were raised. The specificity of the antisera was confirmed by dot blotting, Western blotting and by immunogold labelling of isolated gap junctions. One antiserum (that raised to residues 131-142) was found to be particularly effective as a cytochemical probe. An immunofluorescence labelling procedure for use with confocal scanning laser microscopy was developed to enable the three-dimensional precision mapping of gap junctions through thick slices of cardiac tissue.(ABSTRACT TRUNCATED AT 400 WORDS)
Animals↗
Reduced content of connexin43 gap junctions in ventricular myocardium from hypertrophied and ischemic human hearts.
BACKGROUND: Gap junctions are a determinant of myocardial conduction. Disturbances of gap-junctional content may account for abnormalities of impulse propagation, contributing to the arrhythmic tendency and mechanical inefficiency of ischemic and hypertrophied myocardium. The aim of this study was to characterize gap junction organization in normal human ventricular myocardium and to establish whether abnormalities exist in myocardium of chronically ischemic and hypertrophied hearts. METHODS AND RESULTS: Cardiac gap-junctional connexin43 antibodies and confocal microscopy were used in a quantitative immunohistochemical study of surgical myocardial samples to explore the structural basis of electromechanical ventricular dysfunction in chronic ischemic and hypertrophic heart diseases. Normal adult human left ventricular myocardium had a gap-junctional surface area of 0.0051 micron2/micron3 myocyte volume; gap junctions were confined to intercalated disks, of which there was a mean of 11.6 per cell. The right ventricle showed similar gap junction surface area. Left ventricular myocardium from ischemic hearts (distant from any fibrotic scarring), despite normal numbers of intercalated disks per cell, had a reduced gap junction surface area (0.0027 micron2/micron3; P = .02), as did hypertrophied myocardium (0.0031 micron2/micron3; P = .05). The cardiac myocytes in the pathological tissues were larger than normal, and estimated gap-junctional content per cell was reduced in ischemic ventricle (P = .02) compared with normal. CONCLUSIONS: Gap junctions in normal adult human working ventricular myocardium occupy an area of 0.0051 micron2/micron3 myocyte volume. This surface area is reduced in ventricular myocardium from hearts subject to chronic hypertrophy and ischemia, despite a normal number of intercellular abutments, and this alteration may contribute to abnormal impulse propagation in these hearts.
Adult↗
Validation of immunohistochemical quantification in confocal scanning laser microscopy: a comparative assessment of gap junction size with confocal and ultrastructural techniques.
Confocal scanning laser microscopy (CSLM) is increasingly being used to image antibody-labeled structures visualized with a fluorescent secondary antibody. Such digital images are routinely stored on computer and are well suited to quantitative analysis. Although theoretical aspects of CSLM imaging and resolution are well defined, information is lacking on the relationship observed between measurements of fluorescent antibody-labeled structures and the size of the same structures as determined by electron microscopy (EM). In the present study we examined this relationship for the cardiac gap junction. Data on the size of immunofluorescent-labeled gap junctions were acquired by two methods of analysis from CSLM images and compared statistically with measurements of gap junction size obtained by freeze-fracture EM. The freeze-fracture data were compared before and after exclusion of small junctions, corresponding to those that theoretically would not have been detected in CSLM analysis. The data obtained by the different methods were similar but not identical, reflecting the advantages and limitations of each technique. However, the comparison did indicate that with appropriate sample preparation and orientation, accurate and rapid analysis can be achieved by CSLM, particularly when digital semi-automated techniques are employed.
Animals↗
Arrhythmias after the Fontan procedure.
OBJECTIVE: To study the determinants and outcome of arrhythmias after the Fontan type operation. DESIGN: Retrospective analysis of data in patients operated on between 1972 and 1986 (follow up 5-19 years (mean 12 years)). PATIENTS: All 60 patients undergoing a Fontan type procedure at the National Heart Hospital, London, during the study period (mean age (SD) 12.3 (6.8) years). RESULTS: Postoperative arrhythmias occurred in 34 patients (57%), and 11 (58%) of 19 early postoperative deaths (within seven days) were related to arrhythmias. Early arrhythmias occurred in 19 (32%) patients of whom 11 (58%) died. All patients with early atrial fibrillation and His bundle tachycardia died and only preoperative atrial fibrillation recurred early. There was a higher incidence of early arrhythmias, which were less well tolerated, in double inlet single ventricle patients (9/19) than in those with tricuspid atresia (8/37). There were no other preoperative determinants of early arrhythmias or deaths from early arrhythmia. Late (after seven days) arrhythmias occurred in 15 (37% of hospital survivors). They had higher right atrial (RA) pressures both early and late after operation and had lower ventricular ejection fractions late after operation. Of those with atrial arrhythmias 86% had RA obstruction and 57% had an RA thrombus or pulmonary embolism at presentation; this was also confirmed in two patients in whom late sudden deaths occurred. Atrial fibrillation early after reoperation for RA obstruction was fatal. The actuarial arrhythmia free survival for hospital survivors was 60% at 10 years. CONCLUSIONS: Early postoperative arrhythmias were poorly tolerated, particularly atrial fibrillation and His bundle tachycardia. Previous atrial fibrillation was a relative contraindication to this procedure. Late postoperative arrhythmias were associated with higher RA pressures measured both early and late after operation and worse late ventricular function. Late arrhythmias may be the first manifestation of RA obstruction, which must be sought. RA thrombus was common in patients with atrial arrhythmias and should be treated early with anticoagulants.
Adolescent↗
Myocarditis--continuing clinical and pathologic confusion.
Explore the source record for details and available documents.
Biopsy↗
Myocarditis--a controversial disease.
Explore the source record for details and available documents.
Bacterial Infections↗
Altered patterns of gap junction distribution in ischemic heart disease. An immunohistochemical study of human myocardium using laser scanning confocal microscopy.
Arrhythmias are a common and potentially life-threatening complication of myocardial ischemia and infarction in humans. The structural pathways for the rapid intercellular conduction of the electrical impulse that stimulates coordinated contraction in the myocardium are formed by the gap junctions situated at intercalated disks. By raising antibodies to cardiac gap-junctional protein, and using these antibodies in an immunohistochemical procedure in combination with the technique of laser scanning confocal microscopy, we have succeeded in localizing gap junctions, with a clarity not previously possible, through thick volumes of human myocardial tissue. To explore the structural basis for ischemia and infarction-related arrhythmogenesis, antibody labeling and laser scanning confocal microscopy were applied to study the organization, distribution, and other characteristics of gap junctions in the explanted hearts of patients undergoing cardiac transplantation for advanced ischemic heart disease. In areas of myocardium free from histologically detectable structural damage, there was no significant difference in the size of distribution of labeled gap junctions, or in their number per intercalated disk, between left ventricular tissue (in which functional impairment was severe) and right ventricular tissue (in which functional impairment was minimal). However, in myocytes at the border of healed infarcts--zones to which the slow conduction responsible for reentry arrhythmias has been localized--the organization of gap junctions was markedly disordered; instead of being aggregated into discrete intercalated disks, gap-junctional immunostaining was spread extensively over myocyte surfaces. Some infarct zones were bridged by continuous strands of myocytes, coupled to one another by gap junctions, thereby linking healthy myocardium on either side. At their thinnest, these bridges were in some instances no wider than a single attenuated myocyte. The conclusions are 1) a widespread, generalized derangement of gap junction organization does not appear to underlie functional impairment in the ischemic heart, 2) a disorderly arrangement typifies gap junctions in myocytes of the infarct border zone, and this may contribute to alterations in conduction that are capable of precipitating reentry arrhythmias, and 3) delicate chains of myocytes traverse some healed infarcts, apparently forming electrically coupled bridges across what would otherwise constitute blocked zones. The weakest link in this chain can be a single, degenerating myocyte; avoidance of arrhythmia may therefore depend on the continued survival of this single cell.
Antibodies↗
Pneumococcal cellulitis: a rare manifestation of pneumococcaemia in adults.
An elderly woman with rheumatoid arthritis of 8 years duration and for which she was receiving indomethacin, developed multifocal cellulitis with subsequent necrosis. Streptococcus pneumoniae type 1 was isolated from her blood and from blister fluid. Previous reported cases are summarised.
Aged↗
Platelet hyperreactivity and inefficient spontaneous thrombolysis in patients at high risk from an acute coronary event.
We conducted a retrospective study to correlate thrombotic variables with the risk from an acute coronary event, using a new in vitro technique, which measures haemostasis, thrombolysis and coagulation from non-anticoagulated blood samples. The analysis was based on data from 63 patients who had undergone exercise radionuclide ventriculography, 50 of whom were considered to be at risk from an acute coronary event because they satisfied at least one of the following three criteria: (1) coronary angiography documented disease, (2) prior myocardial infarction, (3) ventriculography assessed provocable ischaemia. Fifty matched normal subjects were used as controls. Significantly enhanced haemostasis was measured in patients considered at risk from acute coronary event, and haemostatic activity was further increased in patients with provocable ischaemia. Haemostasis in eight patients at risk (provocable ischaemia), who continued with the medication during the test, did not differ significantly from the controls. Greatly reduced spontaneous thrombolytic activity was measured in all patients at risk from acute coronary events. These findings suggest the presence of hyperactive platelets in patients at risk from acute coronary events, with an additional risk of greatly reduced spontaneous thrombolytic activity.
Adult↗