Ultrastructural stereological analysis of acute myocardial hypertrophy of hypertensive etiology

The myocardium of Wistar rats was studied by electron microscopy after ligation of the renal artery resulting in a stable elevation of blood pressure. The ultrastructural data on the development of heart hypertrophy were described within 5 to 35 days after operation using the morphometric and stereological methods and correlation analysis. The hypertrophied cardiomyocytes showed a reduction in the ratio of the total volume density of the mitochondria, sarcoplasmic reticulum and T system to the volume density of myofibrils. It was discovered that hypertrophy of cardiomyocytes is marked by an increase in the sarcoplasmic reticulum rather than in myofibrils and other cell compartments, whereas the relative volume of mitochondria decreases.     

Ultrastructural morphometry of the myocardium of Thunnus alalunga

The common ventricle in the heart of the Thunnus alalunga was studied. The ventricular myocardium consists of an outer compact layer and a thick inner spongy layer. The compact layer has slightly larger cells (4-6 microns diameter) than the spongy layer (2.5-5 microns diameter). Ultrastructurally the myocardium displays normal arrangements of myofibrils and mitochondria. The sarcoplasmic reticulum is poorly developed. The intercalated discs are simple with the fascia adherens being the most frequent junctional type observed; occasionally a desmosome was seen. Nexus type junctions are present but are unassociated with the intercalated discs. There are no t-tubules evident but the plasmalemma exhibits numerous caveolae which rarely form couplings with the sarcoplasmic reticulum. A morphometric analysis of the volume percent of mitochondria and myofibrils showed that the myocardial cells in the spongy layer of the heart have a significantly greater volume percentage of mitochondria than the compact layer. No significant differences were found between myocardial regions when the volume percentages of myofibrils were compared. The physiological studies revealed that the albacore tuna has heart rates (120 bpm) and ventricular blood pressures (100 mmHg) that are among the highest reported for fish.     

Stereological analysis of the ultrastructural organization of the cardiomyocytes in the red-cheeked suslik in different seasons of the year

The myocardium of red-cheeked sousliks was studied at different seasons with the use of stereological analysis. The volume and surface densities of the myofibrils, mitochondria, T system, sarcoplasmic reticulum as well as the surface-volume ratios of the main organelles were measured. Pronounced seasonal changes in physiological activity of the heterothermal animals were accompanied by marked reorganization of the spatial ultrastructure of the cardiomyocytes. The seasonal regression of the heart weight and diminution of the cardiomyocyte diameter were recorded during hibernation. The authors believe that the increased volume ratio of the cytoplasmic organelles to the myofibrils forms the basis for a rapid adaptive reaction of the heart during hibernation and waking up.     

Structural and functional heterogeneity of cardiomyocytes during hemodynamic loading of the rat heart

Ultrastructural studies of cardiomyocytes during experimental aorta coarctation enabled one to divide them into 6 types: with mitochondrial swelling and enlargement of the sarcoplasmic reticulum; with primary damage to myofibrils; with disintegration of ultrastructure because of edema; with hypertrophy and hyperplasia of ultrastructures; without essential changes in organelles; and with concomitant changes in mitochondria and myofibrils. Such different reactions of cardiomyocytes are regarded as an adaptation mechanism that ensures the maintenance of heart function under extreme conditions.     

The organization of the sarcoplasmic reticulum in teleost ventricular myocardial cells

Summary The morphology of the sarcoplasmic reticulum in myocardial cells of the ventricle of the trout heart is described as the result of an investigation with the electron microscope. The sarcoplasmic reticulum is sparse in distribution compared to that of birds or mammals but shows a fundamentally similar organization. A very loose network of fine tubules is in intimate contact with the myofibrils but with no local modification with respect to the arrangement of myofilaments within the sarcomeres. There is no special association of the sarcoplasmic reticulum with the Z-bands. Some tubules pass to the cell periphery where they expand to form subsarcolemmal cisternae in which electron-dense matter is often seen. The occurrence of the subsarcolemmal cisternae (peripheral couplings) is random and they are not observed in the vicinity of intercalated discs. The sarcoplasmic reticulum is discussed in relation to excitation-contraction coupling in teleost myocardial cells, and in comparison with that of other vertebrates.I am grateful to Professor J. D. Lever for making certain facilities available, and to Mr. P. F. Hire for photographic assistance.     

Early ultrastructural changes in the myocardium following thyroxine-induced hypertrophy

The model of myocardial hypertrophy induced by thyroxine was studied with particular regard to the early ultrastructural changes in fractional volume of the mitochondria and myofibrils, and capillary distribution. Following injections of L-thyroxine (25 mg/kg IP) for 9 consecutive days, rats were sacrificed by vascular perfusion and cardiac tissue samples from the mid-wall zone of the left ventricle were processed routinely for electron microscopy. Heart weight/body weight ratios of thyroxine treated (T) rats showed a significant increase (P less than 0.001) over the ratios in control (C) rats. Likewise, the fractional volume of mitochondria (42%) was significantly increased (P less than 0.001) in the myocardium of T rats when compared with C rats (31%). However, the fractional volume of myofibrils was significantly decreased in the myocardium of T rats (P less than 0.001) and there was no significant difference between the hearts of T and C rats with respect to capillary luminal area/myocyte area. The mitochondria/myofibril ratio was increased in the hearts of T rats (0.82) over that found in control hearts (0.52). These results suggest that in the early stages of thyroxine-induced myocardial hypertrophy there is not an immediate increase in capillary area which may account for the ischemia and significant increase in mitochondrial volume which characterized myocardial hypertrophy in this model.     

Ultrastructure of the skeletal muscle fibers of athletes with various specializations and qualifications

An electron microscopic investigation of the skeletal muscle bioptates has been performed in 80 volunteer-sportsmen of different qualification specializing in race rowing and in skating. Common for all the sportsmen examined are those peculiarities in ultrastructural organization of the skeletal muscle fibers that demonstrate their adaptation to an increased muscle activity. Specificity of ultrastructural organization of the skeletal muscle fibers is revealed in connection with sportive specialization. Speed-force trainings in skater-sprinters produce hypertrophy of myofibrils; more often than other sportsmen they demonstrate dilatation of cisterns in the sarcoplasmic reticulum, appearance of granular inclusions in mitochondrial matrix. In skater-statyers sarcoplasm of muscle fibers sharply increases in volume. Sometimes, loading for endurance in skater-stayers produces rather essential disturbances in structure of muscle fibers up to their necrosis. In muscles of these sportsmen processes of "intracellular" regeneration are most distinctly observed.     

The ultrastructure of the heart of Oniscus asellus L. and Asellus aquaticus L. (Crustacea,Isopoda)

Summary The endocardium of Oniscus asellus L. and Asellus aquaticus L. consists of lipid cells. The epicardium consists of a layer of cells with a vesiculated cytoplasm covered by a thick extracellular fibrous sheet. The myocardium is a single layer of cells, the sarcolemma invaginates at Z disc level forming transverse tubules, and longitudinal tubules branch off from these. At the A-I level' longitudinal tubules form transverse systems, which form couplings with the sarcoplasmic reticulum. The sarcoplasmic reticulum appears as perforated sheets enveloping the myofibrils. Two types of nerve terminal are found: one is embedded in a myocardial cell process, the other lies in a myocardial cell depression. They contain clear and dense-cored synaptic vesicles.This work was supported by grants from the Norwegian Research Council for Science and the Humanities     

Myofiber damage accompanying intramuscular parasitism by Sarcocystis muris

Myofiber degeneration which results from Sarcocystis infection exhibits a number of fine structural features suggestive of other myopathies and several well-defined fine structural features not characteristic of other myopathies. Some of these fine structural features are similar to those observed in intramuscular infections of Trichinella spiralis, another muscle parasite. Major alterations of the myofibrillar contractile apparatus occur at the periphery of the membrane bound parasitophorous vacuole which include splitting and fragmentation of the myofibrils at the longitudinal ends of the parasitophorous vacuole and Z line dissolution at the radial periphery. Membranous structural elements including mitochondria, sarcoplasmic reticulum and T system components become disarrayed as the myofibrils degenerate. Some minor hypertrophy of the sarcoplasmic reticulum occurs in conjunction with initial fragmentation of the myofibrils bu no major dilation or hypertrophy has been observed. There is a distinctive membranous organization of the interface of the parasitophorous vacuole. The presence of pycnotic and fragmenting nuclei, sarcolemmal invaginations with accompanying fibrous connective tissue invasion and large areas of undifferentiated cytoplasm suggest the ultimate necrosis and destruction of infected myofibers. The similarity between morphological features of myofibrillar degeneration accompanying intramuscular Sarcocystis muris infections and those associated with a variety of myopathies resulting from other causes suggests that a common mechanism of muscle response to damage might result in the observed structural degeneration.     

THE SARCOPLASMIC RETICULUM AND ITS ASSOCIATION WITH THE T SYSTEM IN AN INSECT

The fine structure of the sarcoplasmic reticulum and the transverse tubular system of the femoral muscle of the cockroach, Leucophaea maderae, was studied after prefixation in glutaraldehyde, postfixation in osmium tetroxide, and embedding in Epon. The sarcoplasmic reticulum in this muscle reveals features not previously reported. The sarcoplasmic reticulum is abundant, consisting mainly of a fenestrated envelope which surrounds each myofibril at all levels in the sarcomere. This sarcoplasmic reticulum envelope is continuous transversally as well as longitudinally along the myofibrils. Dyadic junctions are formed by a single T system element which contacts the unfenestrated sarcoplasmic reticulum of adjacent myofibrils in an alternating manner at the ends of the A band. At the dyads, regularly spaced thickenings of the sarcoplasmic reticulum membranes bordering the dyadic spaces are noted. These thickenings, however, do not contact the T tubule membrane. Typical dyadic contacts also are seen between the cell surface membrane and sarcoplasmic reticulum. Z line-like material is seen in contact with the membranes of the cell surface and longitudinal branches of the T systems.     

Correction of stress-induced disorders of the ultrastructure of hypertrophied myocardium with thyroid hormones

In the experiment performed on 25 non-inbred male rats ultrastructural changes in cardiomyocytes of the hypertrophied heart have been studied under conditions of stress caused by immobilization and possibility to correct these changes by means of thyroid hormones. The stress intensifies destructive lesions in a number of organelles++, which develop at a prolonged hypertrophy, decreases essentially the ratio mitochondria/myofibrils in section area. Small doses of the thyroid hormones protect the hypertrophied heart from the damaging effect of the stress: prevent the stress-induced+ decrease in the ratio mitochondria/myofibrils, as well as stimulate development of the regenerative-adaptive processes (increase in size and number of mitochondria and their crists, elements of the sarcoplasmic reticulum, glycogen granules, increase in section areas of their nuclei and chromatin in them). The thyroid hormones restrict essentially decrease in correlation of organelles++, resulted from hypertrophy. Thus, the stress-induced disturbances in ultrastructure of the hypertrophied heart can be prevent by means of the thyroid hormones, administered in small doses.     

Somatic Musculature of Trichodorus porosus and Criconemoides similis

The somatic musculature of Trichodorus porosus is transversely striated, and that of Criconemoides similis is obliquely striated. The species also differ in configuration of the myofibrils, arrangement of the filaments within the myofibrils, and abundance of sarcoplasmic reticulum. Both species are platymyarian and meromyarian. The muscle cells are composed of myofibrils, sarcoplasm, sarcoplasmic reticulum, and various organelles. The myofibrils of both species contain actin and myosin filaments.     

Effect of chronic stress on the ultrastructure of the myocardium and hypothalamus of "emotional" and "nonemotional" rats

The influence of chronic stress on the ultrastructure of the myocardium and hypothalamus was studied in experiments on male rats with different levels of emotional-behavioral reactivity. "Emotional" rats manifested a pronounced increase in glycogen granules in myocytes and intercellular space, appearance of the areas of overcontraction of myofibrils, conglomerates of aggregated platelets in myocardial capillaries, and red cell egress from myocardial and hypothalamic capillaries. Alterations in the ultrastructure of the myocardium and hypothalamus in "nonemotional" rats were less marked and consisted in the appearance of the areas of overcontraction of myofibrils, enlargement of sarcoplasmic reticulum caverns, and in an increase in the lipid content in cardiomyocytes. The ultrastructural changes in the myocardium and hypothalamus of "emotional" and "nonemotional" rats indicate different reactivity of the animals and are likely to be accounted for by different levels of activation of their adrenergic systems.     

Discontinuity of sarcoplasmic reticulum in the mid-sarcomere region in flight muscle of dragonflies

The sarcoplasmic reticulum organization of dragonfly flight muscles is analyzed, with particular reference to the doubling existing at H-band level. This doubling could be explained as a consequence of a regular discontinuity in the sarcoplasmic reticulum covering myofibrils. In each sarcomere, two sleeves of the sarcoplasmic reticulum seem to overlap forming a telescopic system which can slide outside each other during the lengthening and shortening movements of the fiber.     

Mechanisms of cardiodepression by an Na+-H+ exchange inhibitor methyl-N-isobutyl amiloride (MIA) on the heart: lack of beneficial effects in ischemia-reperfusion injury

Although Na+-H+ exchange (NHE) inhibitors such as methyl-N-isobutyl amiloride (MIA) are known to depress the cardiac function, the mechanisms of their negative inotropic effect are not completely understood. In this study, isolated rat hearts were perfused with MIA to study its action on cardiac performance, whereas isolated subcellular organelles such as sarcolemma, myofibrils, sarcoplasmic reticulum, and mitochondria were treated with MIA to determine its effect on their function. The effect of MIA on intracellular Ca2+ mobilization was examined in fura-2-AM-loaded cardiomyocytes. MIA was observed to depress cardiac function in a concentration-dependent manner in HCO3- -free buffer. On the other hand, MIA had an initial positive inotropic effect followed by a negative inotropic effect in HCO3-containing buffer. MIA increased the basal concentration of intracellular Ca2+ ([Ca2+]i) and augmented the KCl-mediated increase in [Ca2+]i. MIA did not show any direct effect on myofibrils, sarcolemma, and sarcoplasmic reticulum ATPase activities; however, this agent was found to decrease the intracellular pH, which reduced the myofibrils Ca2+-stimulated ATPase activity. MIA also increased Ca2+ uptake by mitochondria without having any direct effect on sarcoplasmic reticulum Ca2+ uptake. In addition, MIA did not protect the hearts subjected to mild Ca2+ paradox as well as ischemia-reperfusion-mediated injury. These results suggest that the increase in [Ca2+]i in cardiomyocytes may be responsible for the initial positive inotropic effect of MIA, but its negative inotropic action may be due to mitochondrial Ca2+ overloading as well as indirect depression of myofibrillar Ca2+ ATPase activity. Thus the accumulation of [H+]i as well as occurrence of intracellular and mitochondrial Ca2+ overload may explain the lack of beneficial effects of MIA in preventing the ischemia-reperfusion-induced myocardial injury.     

Creatine kinase in subcellular components of the rabbit myocardium during experimental obstruction of the coronary circulation

Acute myocardial ischemia (intravenous 0.2 U/kg vasopressin infusion) is shown to cause various changes in the creatine kinase isoenzyme activity: it decreases in mitochondria and sarcoplasmic reticulum and increases in myofibrils and cytosol, no significant alterations taking place in sarcolemma. It may be suggested that the stated changes are important components of the complex adaptational reactions which occur in the ischemic myocardium and support its main contractional function.     

Implications of protease activation in cardiac dysfunction and development of genetic cardiomyopathy in hamsters

It has become evident that protein degradation by proteolytic enzymes, known as proteases, is partly responsible for cardiovascular dysfunction in various types of heart disease. Both extracellular and intracellular alterations in proteolytic activities are invariably seen in heart failure associated with hypertrophic cardiomyopathy, dilated cardiomyopathy, hypertensive cardiomyopathy, diabetic cardiomyopathy, and ischemic cardiomyopathy. Genetic cardiomyopathy displayed in different strains of hamsters provides a useful model for studying heart failure due to either cardiac hypertrophy or cardiac dilation. Alterations in the function of several myocardial organelles such as sarcolemma, sarcoplasmic reticulum, myofibrils, mitochondria, as well as extracellular matrix have been shown to be due to subcellular remodeling as a consequence of changes in gene expression and protein content in failing hearts from cardiomyopathic hamsters. In view of the increased activities of various proteases, including calpains and matrix metalloproteinases in the hearts of genetically determined hamsters, it is proposed that the activation of different proteases may also represent an important determinant of subcellular remodeling and cardiac dysfunction associated with genetic cardiomyopathy.     

Ultrastructural distribution of the S100A1 Ca2+-binding protein in the human heart

Impaired calcium homeostasis and altered expression of Ca2+-binding proteins are associated with cardiomyopathies, myocardial hypertrophy, infarction or ischemia. S100A1 protein with its modulatory effect on different target proteins has been proposed as one of potential candidates which could participate in these pathological processes. The exact localization of S100A1 in human heart cells on the ultrastructural level accompanied with biochemical determination of its target proteins may help clarify the role of S100A1 in heart muscle. In the present study the distribution of the S100A1 protein using postembedding (Lowicryl K4M) immunocytochemical method in human heart muscle has been determined quantitatively, relating number of antigen sites to the unit area of a respective structural component. S100A1 antigen sites have been detected in elements of sarcoplasmic reticulum (SR), in myofibrils at all levels of sarcomere and in mitochondria, the density of immunolabeling at Z-lines being about 3 times and at SR more than 5 times higher than immunolabeling of remaining structural components. The presence of the S100A1 in SR and myofibrils may be related to the known target proteins for S100A1 at these sites.     

Seasonal changes in the cardiomyocytes of heterothermal animals

In 20 Citellus erythrogenys the volumetric and surface densities of myofibrils, mitochondria, sarcoplasmic reticulum, T-system and lipid drops were estimated in cardiomyocytes by means of stereological methods before, during and after hibernation. The volumetric and surface-volumetric ratios for the main intracellular compartments were calculated. Certain morphological criteria were found for the seasonal peculiarities in the structural organization of cardiomyocytes in the hibernating rodents. During hibernation, myocardial atrophy (seasonal regression of the heart weight and decreasing diameter of cardiomyocytes) takes place. It is accompanied with an adaptive rearrangement of the cardiomyocyte ultrastructure. The latter facilitates to myocardial contractility at low body temperatures at the expense of activation of the cellular transport-energic interaction system.     

Binding of an ankyrin-1 isoform to obscurin suggests a molecular link between the sarcoplasmic reticulum and myofibrils in striated muscles

Assembly of specialized membrane domains, both of the plasma membrane and of the ER, is necessary for the physiological activity of striated muscle cells. The mechanisms that mediate the structural organization of the sarcoplasmic reticulum with respect to the myofibrils are, however, not known. We report here that ank1.5, a small splice variant of the ank1 gene localized on the sarcoplasmic reticulum membrane, is capable of interacting with a sequence of 25 aa located at the COOH terminus of obscurin. Obscurin is a giant sarcomeric protein of approximately 800 kD that binds to titin and has been proposed to mediate interactions between myofibrils and other cellular structures. The binding sites and the critical aa required in the interaction between ank1.5 and obscurin were characterized using the yeast two-hybrid system, in in vitro pull-down assays and in experiments in heterologous cells. In differentiated skeletal muscle cells, a transfected myc-tagged ank1.5 was found to be selectively restricted near the M line region where it colocalized with endogenous obscurin. The M line localization of ank1.5 required a functional obscurin-binding site, because mutations of this domain resulted in a diffused distribution of the mutant ank1.5 protein in skeletal muscle cells. The interaction between ank1.5 and obscurin represents the first direct evidence of two proteins that may provide a direct link between the sarcoplasmic reticulum and myofibrils.In keeping with the proposed role of obscurin in mediating an interaction with ankyrins and sarcoplasmic reticulum, we have also found that a sequence with homology to the obscurin-binding site of ank1.5 is present in the ank2.2 isoform, which in striated muscles has been also shown to associate with the sarcoplasmic reticulum. Accordingly, a peptide containing the COOH terminus of ank2.2 fused with GST was found to bind to obscurin. Based on reported evidence showing that the COOH terminus of ank2.2 is necessary for the localization of ryanodine receptors and InsP3 receptors in the sarcoplasmic reticulum, we propose that obscurin, through multiple interactions with ank1.5 and ank2.2 isoforms, may assemble a large protein complex that, in addition to a structural function, may play a role in the organization of specific subdomains in the sarcoplasmic reticulum.