[Characteristic electrolyte changes in the hereditary myopathy and cardiomyopathy of the Syrian golden hamster (strain BIO 8262) (author's transl)]

Ultrastructural calcium distribution and myocardial calcium content in human idiopathic dilated cardiomyopathy

Myocardial calcium overload in chronic heart failure is still a debatable issue. The aim of this study was to investigate the myocardial calcium content and intracellular calcium distribution in end-stage dilated cardiomyopathy. The explanted hearts of 13 patients (9 male, 4 female, mean age 49 ± 12 years) undergoing heart transplantation because of end-stage dilated cardiomyopathy were examined. Samples were obtained from the right and left ventricular free wall and from the septum. Calcium and magnesium content were measured by atomic absorption spectrophotometry. Ultrastructural calcium distribution was examined in dilated cardiomyopathy using the phosphate-pyroantimonate method. Ultrastructural calcium distribution was also examined in left ventricular biopsies obtained from 3 patients (male, mean age 47 ± 3.6 years) with nonfailing hearts. The number of mitochondrial calcium precipitates was estimated morphometrically by a point counting method. Myocardial calcium and magnesium content in dilated cardiomyopathy did not differ significantly among the right and left ventricles and septum ranging from 8.5 to 10.8 mmol/kg dry weight. The phosphate-pyroantimonate method visualized calcium precipitates being confined to the sarcolemma, T-tubules, intercalated disks, and mitochondria in both nonfailing myocardium and dilated cardiomyopathy. Because mitochondria may act as buffers of cytoplasmic calcium, mitochondrial calcium precipitates served as a criterion for a possible cellular calcium overload. No differences in the amount of mitochondrial calcium deposits were observed between dilated cardiomyopathy and nonfailing hearts. The data suggest that there is no global myocardial calcium overload in human eng-stage dilated cardiomyopathy.

Enhanced alpha 1-adrenergic responsiveness in cardiomyopathic hamster cardiac myocytes. Relation to the expression of pertussis toxin-sensitive G protein and alpha 1-adrenergic receptors

The pathogenesis of the myopathy occurring in the heart of the cardiomyopathic strain of the Syrian hamster is not well understood but is believed to be associated with abnormal calcium handling by myopathic cells. The purpose of this study was to determine whether the cardiomyopathy occurring in strain BIO 14.6 animals is associated with an enhanced alpha 1-adrenergic receptor-mediated rise in cytosolic calcium, whether a pertussis toxin-sensitive G protein is involved in coupling the alpha 1-adrenergic receptor to changes in intracellular calcium and whether enhanced alpha 1 responsiveness is associated with an increase in the level of expression of the alpha 1-adrenergic receptor or in the pertussis toxin-sensitive G protein or proteins. To test the hypothesis that the cardiomyopathic state is associated with a greater alpha 1-receptor-mediated rise in cytosolic calcium, we studied the effect of phenylephrine (in the presence of propranolol) on time-averaged cytosolic calcium concentration ([Ca2+]i) in isolated cardiac myocytes from cardiomyopathic and age-matched control hamsters. Phenylephrine caused a greater increase both in time-averaged [Ca2+]i (an increase of 48 +/- 8% versus 12 +/- 3%, p less than 0.01) and in contractility (+181 +/- 22% versus +35 +/- 9%, p less than 0.01) in cardiomyopathic than in normal cardiac myocytes. Exposure to pertussis toxin (200 ng/ml for 3 hours) attenuated the alpha 1-adrenergic receptor-mediated increase in contractility and time-averaged [Ca2+]i in both cardiomyopathic and normal cells. The level of pertussis toxin-sensitive G protein, as determined by pertussis toxin-mediated [32P]ADP-ribosylation, was 1.6-fold higher in cardiomyopathic versus normal hamster hearts. The density of alpha 1-adrenergic receptors, as measured by the antagonist radioligand [3H]prazosin and the affinity of the receptor for agonist and antagonist were similar in myopathic and normal heart membranes. Thus, in cardiac myocytes from hamsters, the alpha 1-adrenergic receptor-mediated effects on [Ca2+]i and contractility appear to be mediated by a pertussis toxin-sensitive G protein or proteins. In myocytes from cardiomyopathic hamsters, these alpha 1-adrenergic effects were increased in magnitude, as was the level of pertussis toxin-sensitive G protein, but there was no measurable alteration in the density or ligand binding properties of alpha 1-adrenergic receptors.

Calcium overload in human giant cell myocarditis

Myocardial calcium overload was observed in a patient with giant cell myocarditis. The myocardial calcium content estimated by atomic absorption spectrophotometry amounted to 120 mEq/kg dry weight, and the von Kossa stain disclosed multiple foci with patchy calcifications of myocardial fibres. Cytochemical examination of the ultrastructural calcium localisation using the phosphate-pyroantimonate method showed considerable variation in the subcellular calcium distribution. In normal myocytes calcium precipitates were confined to the inner leaflet of the sarcolemma, T-tubules, intercalated disks, and sporadically to mitochondria. In contrast, extensive calcification of mitochondria and loss of sarcolemmal calcium was evident in necrotic myocytes. A number of grossly normal myocytes also showed an increase of calcium precipitates in slightly swollen mitochondria. These findings suggest that myocardial calcium overload in this case started in viable myocytes and was not merely a secondary phenomenon occurring after cell death.

Catecholamines, calcium and cardiomyopathy

The cardiomyopathic Syrian hamster has a genetically transmitted form of dilated cardiomyopathy and is an important paradigm of myocardial disease, particularly for studies addressing the earliest stages of myocardial dysfunction. This model exhibits an increase in cardiac sympathetic tone in the presence of an altered expression of sarcolemmal calcium channels or of alpha 1 receptors, and a defective handling of calcium by both cardiomyocytes and vascular smooth muscle cells. Increased expression of the oncogene c-myc is evident in cardiomyocytes before any overt evidence of heart disease. Alterations in a nuclear phosphoprotein, which appears to be important in the regulation of gene expression, have also been identified. The disease becomes phenotypically manifest by the development of microvascular spasm, reperfusion injury and myocyte loss. Myocyte loss, in turn, burdens the remaining cells with an increasing load, increasing sympathetic stimulation, myocyte hypertrophy and further cell loss--a continuing vicious spiral that culminates in the development of myocardial failure. All of the features of hamster cardiomyopathy may be prevented by the administration of verapamil or prazosin to juvenile hamsters before the phenotypic onset of their heart disease. This understanding has led to the study of new imaging agents that promise the detection of such forms of cardiomyopathy in their earliest stages and a means by which the effects of therapy can be assessed. If such mechanisms are applicable to human cardiomyopathy, early treatment of patients with adrenergic antagonists or calcium antagonists should be beneficial.

Intracellular elemental content of cardiac and skeletal muscle of normal and dystrophic hamsters

To test the hypothesis that the genetic lesion causing muscular dystrophy might be reflected in an abnormal intracellular elemental content, the elemental content of individual cardiac and skeletal muscle fibers in 50-day-old male control and cardiomyopathic BIO 53.58 hamsters was determined. The technique of electron probe x-ray microanalysis of freeze-dried tissue was employed. No electrolyte content differences were found between control and diseased animals for nuclei, myofibrillar cytoplasm, or mitochondrially-enriched cytoplasm of cardiac myocytes. Sulfur was elevated in dystrophic cardiac myocytes and was the only element significantly different in heart tissue of control and cardiomyopathic animals. Sulfur was also elevated in dystrophic soleus muscle fibers. The pattern of electrolyte content of these cells reflected a mixture of normal cells and damaged cells with altered electrolyte content. In this hamster model, alteration of electrolyte content of myocytes appears to be a result of the disease process and not an inherent characteristic of muscular dystrophy. The elevated sulfur in dystrophic hamster myocytes reflects a biochemical lesion which deserves further study.

Elements in muscle measured in vivo and in vitro with X-ray spectrometry

Calcium, iron, copper, and zinc concentrations in muscle were measured in vivo by x-ray spectrometry (XRS). The undersurface of the tongue was examined in cardiomyopathic and in normal hamsters. Values were compared to in-vitro analyses of various muscles from the same groups of animals using XRS and chemical analysis. Blood tests as well as histologic and histometric examinations were also performed. The correlated results show that XRS is a relatively sensitive and practical method for measuring chemical elements in muscle, and that it could be developed into a useful clinical test in certain neuromuscular and myocardial diseases. An interesting incidental finding was that, though all the examined muscles of myopathic animals had pathologic changes, only the tongue and myocardium, which are composed exclusively of red fibers, showed excessive calcium accumulation. This suggests either that the basic genetic aberration is not directly related to the oxidative metabolism, or that white muscles have a more efficient system for dealing with calcium overload.

Electron microscopic X-ray microanalysis of localized element concentrations in human cardiomyopathies: a pilot study

The elemental content in localized cellular regions of human myocardial biopsy specimens was studied by electron microscopic x-ray microanalysis. The elements detected were phosphorus, sulfur, chlorine, calcium, and zinc and occasionally tracrs of iron and copper. Nucleoli and heterochromatin contained the highest concentrations of phosphorus and calcium, whereas sulfur was prominent in sarcomeres, dark mitochondria, and secondary lysosomes. Dark mitochondria often had more phosphorus, sulfur, and calcium than swollen, paler ones.

Localised concentrations of elements in hamster cardiomyopathy. Electron microscopic x-ray microanalysis of normal and sick myocardia

Localized elemental concentrations of Ca, P, Cl, S, and Zn were detected by X-ray microanalysis during viewing of ultrathin myocardial sections. Cardiomyopathic hamsters were compared with a healthy strain of the same age. Significant increases in calcium and chlorine concentrations were found in sick animals. These were highest in the hypertrophic stage of the disease. Phosphorus and zinc were more variable. Ratios between elements (especially P/Ca) in the same cells and of the same elements in different cell types were found to offer numerical criteria for estimating the degree of pathological change.

Electrocardiographic changes in cardiomyopathic Syrian hamsters (strain BIO 8262)

Under ether anesthesia electrocardiograms were derived from Syrian hamsters (strain BIO 8262) suffering from cardiomyopathy and muscular dystrophy. In addition, ventricular weights and body weight were determined. Young hamsters -- not yet showing morphological signs of the cardiomyopathy with the exception of possible left ventricular hypertrophy -- demonstrated only a longer ventricular activation time than normal hamsters. With the onset of cardiac necrotization left axis deviation in frontal plane projection and right bundle branch blocks are developing in the cardiomyopathic hamsters followed by first degree atrioventricular conduction defects. During the late stage of the cardiomyopathy left bundle branch blocks are additionally arising, while left ventricular hypertrophy is disappearing. Since no overt heart failure is occurring in this strain of cardiomyopathic hamsters, gradual development of high degree conduction defects is assumed to terminate their lives. The electrocardiographic pattern of the hamster cardiomyopathy fits partly into that of human primary as well as secondary cardiomyopathy. Nevertheless, it seems to form an entity of its own, as arrhythmias, higher degree atrioventricular conduction disturbances, typical signs of ventricular or septal hypertrophy, abnormal P and Q waves, ST segment and T wave changes are lacking.