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PubMed1982

Laser diffraction of single intact cardiac muscle cells at rest.

The laser diffraction of single cardiac muscle cells shows distinctive diffraction orders and has the following characteristics. (1) When projected on a screen each diffraction order can be described as an irregular column of fine structures consisting of elliptical spots and short jagged stripes. (2) The fine structures associated with the left and right diffractions of the same diffraction order cannot be correlated according to the plane grating equation, and they do not interchange after the cell has been rotated by 180 degrees around its length. (3) For the same diffraction order, the average diffraction angle of the fine structures as a function of laser incident angle follows the plane grating equation. (4) The meridional diffraction angles of different orders are not related by the plane grating equation. (5) For the same diffraction order, the total intensities of the left and right diffractions are not equal. (6) The left or right intensity of a diffraction column shows a single broad peak as a function of laser incident angle. The incident angles corresponding to the left and right peaks are symmetrical to the axis of normal incidence and are interpreted as the Bragg angles of the Z-discs and the planes formed by the intersections of the A- and I-bands of individual myofibrils. The diffraction measurements are consistent with a model in which the myofibrils are randomly packed in the cell and each myofibril acts as a cylindrical diffractor of one-dimensional order.

Animals↗

PubMedDate not supplied

Rapid changes in myofibrillar proteins after reperfusion of ischemic myocardium in dogs.

The effect of reperfusion on cardiac myofibrillar proteins in the irreversibly injured ischemic myocardium was studied in dogs. Ischemia of the myocardium was produced by complete occlusion of the left anterior descending coronary artery for 90 min (the group of 90I). Occlusion of the coronary artery was then released (reperfusion) for 0.5 min (the group of 90I + 0.5R), 5 min (the group of 90I + 5R), or 20 min (the group of 90I + 20R). In control dogs, the coronary artery was not occluded (the group of no ischemia). Myofibrils (Mfp) were prepared from the myocardium (with centrifugation) in each of the groups, and subjected to electrophoretic analysis in terms of myofibrillar proteins. The yield of Mfs in the groups of 90I, 90I + 0.5R, 90I + 5R, and 90I + 20R was lower than that in the group of no ischemia. There were no marked differences, however, in the electrophoretic pattern of Mfp among the five groups. These results suggest that myofibrils are broken down during reperfusion after ischemia. Therefore, supernatant solution after the first stage of homogenization during the course of preparation of myofibrils (mfs) was also examined. There were many unidentified bands in Mfs, being assumed to be originated from myofibrillar proteins, in the groups of both 90I + 0.5R and 90I + 5R, although these bands were not observed in the group of 90I. These results indicate that degradation of myofibrillar proteins occurs rapidly after reperfusion of the irreversibly injured myocardium. It is uncertain, however, whether reperfusion has a detrimental effect on the reversibly injured myocardium, too.

Actinin↗

PubMedDate not supplied

Contractile proteins in globally "stunned" rabbit myocardium.

The isolated working rabbit heart preparation was used to study whether the "contractile machinery" remains unchanged in globally stunned myocardium. The function of the heart has been measured in nonischemic and postischemic conditions. The effect of isoprenaline or calcium chloride administration in both conditions was also studied. Myocardial contractile function was significantly depressed after 20-min global ischemia and returned to normal after CaCl2 and supranormal values after isoprenaline administration. From hearts used in experiments myofibrils were prepared and their ATPase activity was determined. It was observed that myofibrils prepared from "stunned" myocardium showed about 50% increase in ATPase activity in the presence of CaCl2. Subjection of the heart to ischemia caused a decrease in calcium sensitivity of the myofibrillar ATPase. Myofibrils obtained from ischemic hearts but subjected to isoprenaline or CaCl2 administration exhibited increased calcium sensitivity over that of control heart. These effects were accompanied by changes in the extent of phosphorylation of troponin I (TNI) and myosin light chains. The modification of contractile apparatus in the postischemic period described in this paper may contribute to the overall mechanism of myocardial stunning.

Adenosine Triphosphatases↗

PubMed2004

Sarcomeric determinants of striated muscle relaxation kinetics.

Ca2+ is the primary regulator of force generation by cross-bridges in striated muscle activation and relaxation. Relaxation is as necessary as contraction and, while the kinetics of Ca2+-induced force development have been investigated extensively, those of force relaxation have been both studied and understood less well. Knowledge of the molecular mechanisms underlying relaxation kinetics is of special importance for understanding diastolic function and dysfunction of the heart. A number of experimental models, from whole muscle organs and intact muscle fibres down to single myofibrils, have been used to explore the cascade of kinetic events leading to mechanical relaxation. By using isolated myofibrils and fast solution switching techniques we can distinguish the sarcomeric mechanisms of relaxation from those of myoplasmic Ca2+ removal. There is strong evidence that cross-bridge mechanics and kinetics are major determinants of the time course of striated muscle relaxation whilst thin filament inactivation kinetics and cooperative activation of thin filament by cycling, force-generating cross-bridges do not significantly limit the relaxation rate. Results in myofibrils can be explained well by a simple two-state model of the cross-bridge cycle in which the apparent rate of the force generating transition is modulated by fast, Ca2+-dependent equilibration between off- and on-states of actin. Inter-sarcomere dynamics during the final rapid phase of full force relaxation are responsible for deviations from this simple model.

Animals↗

PubMed1999

Ultrastructural changes in myocardial cells of rats fed a low protein diet.

Ultrastructural changes in the ventricular myocardial cells in rats fed a low protein diet were examined by electron microscopy. The most striking changes were observed in the I-band region of the sarcomeres, which occurred very occasionally in myofibrils. In the sarcomere affected the I-band region was often fractured and/or disintegrated on one side, leaving an extended space, while the opposing I-band region disappeared along with dislocation of the intact A-band toward the adjacent Z-line. This dislocation was presumably attributed to the elasticity of titins connecting between the end of thick filaments and the Z-line. Fractured I-band regions were often accompanied by the dilated sarcoplasmic reticulum in the close vicinity of them. In some myofibrils the streaming and/or disruption of the Z-line were occasionally observed where disarrangement of thick and thin myofilaments were usually present. The study suggests that the fracture of the I-band region, consisting of actin and titin filaments, and the streaming of the Z-line of myofibrils are due to a proteolytic action of calpain and/or cathepsin L, which are activated by leaked Ca2+ ion and/or by modification of internal circumstances of the cytoplasm induced by a low protein diet, thus resulting in a low cardiac output.

Animals↗

PubMed1998

Subcellular localization of dystrophin and vinculin in cardiac muscle fibers and fibers of the conduction system of the chicken ventricle.

The subcellular localization of dystrophin and vinculin was investigated in cardiac muscle fibers and fibers of the conduction system of the chicken ventricle by immunofluorescence confocal microscopy. In ventricular cardiac muscle fibers, strong staining with antibody against dystrophin appeared as regularly arranged transverse striations at the sarcolemmal surface, and faint but uniform staining was seen in narrow strips between these striations. In fibers of the ventricular conduction system, the sarcolemma was stained uniformly with this antibody, but strong staining was found as regular striations in many areas and as scattered patches in other areas of the sarcolemma. These intensely stained striations and scattered patches of dystrophin were colocalized with those of vinculin. Because dystrophin striations were located at the level of Z bands of the underlying myofibrils, they were regarded as the concentration of this protein at costameres together with vinculin. In fibers of the conduction system, myofibrils were close to the sarcolemma where dystrophin and vinculin assumed a striated pattern, at some distance from the cell membrane where these proteins exhibited a patchy distribution, and distant from the sarcolemma where dystrophin was uniformly distributed. These data suggest that the distribution patterns of dystrophin reflect the degree of association between the sarcolemma and underlying myofibrils.

Amino Acid Sequence↗

PubMed1987

The creatine phosphate energy shuttle--the molecular asymmetry of a "pool".

The creatine phosphate shuttle energy transfer mechanism was postulated on the basis of the hexokinase acceptor theory of insulin action. It proposes that the movement of chemical energy from the mitochondrion to the myofibril is in the form of creatine phosphate. This occurs because there are isozymes of creatine phosphokinase bound to the inner membrane of the sarcosome and to the A band of the myofibril. These isozymes have been shown to act as transducers of energy from ATP to creatine phosphate at the translocase site and from creatine phosphate back to ATP at the myofibrillar compartment. Calculations show that there is no significant amount of transformation of creatine phosphate to ATP in the intervening space between the mitochondrion and the myofibril so that, essentially, transport between the oxidative sites and the contractile apparatus is through the creatine phosphate shuttle. There is also evidence that another terminus for this shuttle is the microsome so that muscle activity tends to increase energy supply for protein synthesis.

Adenosine Diphosphate↗

PubMed1983

Myofibrillar creatine kinase in Duchenne and avian muscular dystrophy.

The presence and activity of the fraction of creatine kinase (CK) which was associated with myofibrils and located in the M line of the sarcomeres was determined in normal and dystrophic avian muscle and in normal and dystrophic (Duchenne) human muscle. Myofibrils were isolated from homogenates of muscle and washed nine times so as to remove nonmyofibrillar CK. In myofibrils from dystrophic muscle the enzyme CK was localized to the M line using immunofluorescent techniques and was enzymatically active. These results suggest that in both avian and Duchenne muscular dystrophy, there is not a myofibrillar disorder of the phosphocreatine shuttle.

Adult↗

PubMed1983

Developmental autonomy of muscle fine structure in muscle lineage cells of ascidian embryos.

We have observed ultrastructural features of muscle differentiation in the muscle lineage cells of cleavage-arrested whole embryos and partial embryos of ascidians. Whole embryos of Ciona intestinalis and Ascidia ceratodes were cleavage-arrested with cytochalasin B at the 8-cell stage and reared to an age equivalent to several hours after hatching; these embryos formed extensive myofilaments which were often further organized into myofibrils of different sizes and densities in the peripheral cytoplasm of the two muscle lineage blastomeres (B4.1 pair). Developing myofibrils in cleavage-arrested embryos resembled the muscle elements observed in normal hatched larvae, but were less uniformly organized. A similar development of myofilaments and myofibrils occurred in the muscle lineage cells of multicellular partial embryos reared to "hatching" age. These partial embryos resulted from the isolated muscle lineage pair (B4.1) of blastomeres of the 8-cell stage (Ciona and Ascidia), and from a muscle lineage blastomere pair (B5.2) isolated at the 16-cell stage (Ascidia). Muscle lineage cells in the partial embryos were readily identified by the dense aggregates of mitochondria in their cytoplasm. Taken together, these results from the two kinds of partial embryo effectively eliminate inductive interactions with embryonic tissues other than mesodermal as a necessary factor in the onset of self-differentiation in muscle lineage cells. The relative complexity of muscle phenotype expressed in cleavage-arrested and partial embryos attests to an unusually strong developmental autonomy in the ascidian muscle lineages. This autonomy lends further support to the theory that a localized and segregated egg cytoplasmic determinant is responsible for larval muscle development in ascidian embryos.

Animals↗

PubMed1986

Differentiation without cleavage: multiple cytospecific ultrastructural expressions in individual one-celled ascidian embryos.

Multiple states of differentiation developed within the same undivided egg cytoplasm of ascidian zygotes cleavage-arrested with cytochalasin B. Complex ultrastructural traits of up to four quite diverse cell lineage components were observed in regions of the common cytoplasm in such multinucleate homokaryons of Ciona intestinalis: epidermal, muscle, notochordal, and neural. Almost all specimens among those selected as showing differentiation contained two such features, half of them had at least three, and a few expressed all four. The histospecific morphological characteristics noted were the extracellular test material of epidermal cell origin, muscle myofilaments and myofibrils, sheath components (leaflets and filaments) associated with notochordal cells, and the particular localized combinations of microtubules, filamentous structures, and cilia indicative of neural tissues. Cleavage-arrested one-celled embryos of Ascidia ceratodes served to demonstrate that those which were found cytochemically to contain muscle acetylcholinesterase always had myofibrils and myofilaments. Other arrested zygotes of Ascidia (unstained specimens) also had quite fully formed test material as well as myofilaments and myofibrils. The occurrence within the same cell of so many specific markers of diverse pathways of development is consistent with a theory about a primary level of regulation based on autonomous gene activation factors already present in the fertilized egg. If further investigation substantiates a real cytoplasmic continuity within these cleavage-arrested embryos, other theories that invoke cell interactions, temporal sequences of metabolically distinct microenvironments, and gradients of substances as causes of determinative change seem inadequate to account for the coexisting expressions of differentiation described here.

Cell Differentiation↗

PubMed1991

Distribution of myosin mRNA during development and regeneration of skeletal muscle fibers.

Myosin mRNA distribution among subcellular compartments of anterior tibialis muscles in rabbit is monitored by in situ hybridization. A high density of mRNA was widely distributed throughout myotubes from 29-day fetal muscle and from regenerating adult muscle. All cytoplasmic spaces contained mRNA except where scattered myofibrils and centrally located nuclei were found. In fibers from 22-week-old rabbits, myosin mRNA was concentrated under the sarcolemma and excluded from the consolidated myofibrils and peripheral nuclei. The dispersal of mRNA through the cytoplasm in myotubes suggests that translation of myosin is widespread and that rapid myofibril assembly can occur throughout the fiber.

Animals↗

PubMed1992

The alpha 5 beta 1 integrin associates with a dystrophin-containing lattice during muscle development.

The organization of the alpha 5 beta 1 integrin on skeletal muscle was studied in culture and in sections from adult and embryonic tissue using monoclonal antibodies specific for the alpha 5 subunit. The alpha 5 beta 1 integrin showed changes in organization and in the molecules with which it colocalizes. On early myoblasts, possessing a fibroblast-like morphology, the alpha 5 integrin organization was indistinguishable from that on fibroblasts; it was expressed prominently and localized in numerous focal contacts around the cell periphery. In bipolar myoblasts and early myotubes, the alpha 5 integrin was expressed only weakly and localized in a small number of focal contact-like structures. As myogenesis proceeded there was an apparent increase in integrin expression and a change in organization. In addition to the focal contact-like structures that persist throughout myogenesis in vitro, a dense lattice-like structure of integrin appeared. Fibrillar fibronectin, talin, and non-muscle alpha-actinin did not colocalize with the alpha 5 beta 1 integrin in the lattice structure as they did in the focal contact-like structures. However, dystrophin, which displayed a diffuse distribution earlier, now colocalized with the alpha 5 beta 1 integrin in the punctate lattice. Coincident with the registration of myofibrils into visible sarcomeres, the prominent dense, lattice structure disappeared leaving the focal contact-like structures as the only regions of organized alpha 5 beta 1 integrin. Despite the presence of the beta 1 integrin in neuromuscular or myotendinous junctions in vivo and on myotubes in vitro, the alpha 5 beta 1 integrin was not present in either junction. These observations suggest that the alpha 5 beta 1 integrin is involved in the adhesion of muscle to the extracellular matrix, the organization of the dystrophin-containing lattice, and the organization of nascent myofibrils which emanate from the focal contact- and stress fiber-like structures in muscle. Other integrins appear to anchor myofibrils at the myotendinous and neuromuscular junctions.

Animals↗

PubMed1987

Immunochemical analysis of porcine cardiac C-protein.

C-protein has been isolated from pig heart and its immunochemical properties studied. It is extracted with myosin, and separated from the myosin on a DEAE-Sephadex column. The amount of C-protein recovered from crude myosin is approx. 3.5%. The molecular weight of C-protein is 150,000. Anti-C-protein serum reacts with crude myosin and purified C-protein but not with purified myosin in immunodiffusion plates. Cardiac C-protein does not react with anti-skeletal white muscle C-protein serum. Immunoblotting experiments show that anti-cardiac C-protein serum reacts with a Mr = 150,000 component in myofibrils or crude myosin. C-protein is located in the A-band, except the M-line region, of the myofibrils. These results indicate that C-protein is an intrinsic component of the thick filaments in pig heart myofibrils.

Animals↗

PubMed1991

Distribution of myosin heavy chain mRNA in normal and hyperthyroid heart.

Hyperthyroid treatment produces rapid cardiac cell hypertrophy with all subcellular components increasing in an orderly manner. We compare normal and hyperthyroid tissue in order to relate changes in distribution of myosin mRNA during rapid assembly of myofibrils. At the light microscopic level, in situ hybridization of the ventricular cells shows myosin heavy chain mRNA to be distributed in a spoke-like pattern radiating from the nucleus. Electron microscopy provides the higher resolution necessary to determine mRNA distribution with respect to adjacent sarcomeric and cytoskeletal structures. Papillary muscles were removed from hyperthyroid and normal rabbits, aldehyde fixed, and embedded in LR white. Biotinated riboprobe transcribed from 0.5 kb in the coding region of terminal portion of the rod of alpha-myosin was hybridized and detected by immunocytochemical methods using 5 nm immunoglobulin G gold conjugates. Electron microscopy in situ hybridization runs with same-sense and anti-sense riboprobes were processed and ten micrographs randomly taken from each. Specific cytoplasmic densities of myosin mRNA were calculated by counting clusters of five or more gold particles over respective tissue components after subtraction of background counts. For both normal myocytes and hyperthyroid myocytes, the density of myosin mRNA was about 15 times higher in the cytoskeletal-rich inter-myofibrillar space than in the myofibrils. About half of the myosin mRNA in this inter-myofibrillar region is found within 10 nm of the peripheral filament, but no excess sarcomeric accumulation was seen beside the A-Band. It appears that most of the myosin is translated from mRNA within the inter-myofibrillar space along the entire length of the myofibril periphery. The emerging myosin heavy chain is not directly anchored to the thick filaments in either normal or rapidly growing cardiac cells.

Animals↗

PubMed1977

[Histochemical, quantitative and ultrastructural maturation of human fetal muscle].

Histochemical studies of muscle specimens from human fetuses showed: (a) a uniform fiber type population having the properties of Type IIC fibres up to 19 weeks of development; (b) a progressive appearance of Type I fibres after that age; (c) a decrease in number of Type IIC fibres during the last 3 months of pregnancy, accompanied by the appearance of Type IIB and Type IIA fibres; (d) the presence after the myotube stage of fibers with a light peripheral halo in sections stained for mitochondrial dehydrogenases. Electron-microscopic examination of the muscle fibres confirmed the existence of a peripheral halo devoid of myofibrils and mitochondria and showed: (a) scarcity of myofibrils in comparison with mature muscle fibres and (b) irregularity in shape of the myofibrils. In addition, quantitative studies demonstrated an important variation of the fibre diameters up to 21 weeks and the increase of the mean diameter after this age. It is suggested that the persistence after birth of some features of immaturity identical to those described in this work may be considered as a pathological finding.

Adenosine Triphosphatases↗

PubMed1984

Age-dependent structural changes in the myocardium of rats. A quantitative light- and electron-microscopic study on the right and left chamber wall.

Myocardial fine structure of 6-week-old and 2-year-old female Wistar rats was examined after fixation by perfusion. Qualitatively, lipid droplets, lipofuscin granules and myelin figures were found more often in the older animals. Quantitatively, the volume density of the interstitium of the right ventricular myocardium had significantly increased (52%) in the 2-year-old rats. In these animals a reduction (9%) in the volume fraction of mitochondria in the left ventricular myocytes was seen, while the volume fraction of myofibrils had increased by 10%. The numerical density of mitochondria had significantly increased in the left ventricular myocardium of the older rats by 42%. A decrease in the average size of a mitochondrion by 36% could be shown in the left and by 11% in the right ventricular myocytes of the 2-year-old rats. In these animals the myofibrillar transverse diameter diminished by 15% in the left and by 6% in the right ventricular wall, while the number of myofibrils had increased by 36% and 12%, respectively; these findings signify a close relationship in the number of mitochondria and myofibrils in myocytes. Quantitative alterations in the myocytes of aged rats are more obvious in the left than in the right chamber wall. A reduced mitochondria/myofibril ratio may contribute to the diminished functional adaptability of the aging heart.

Aging↗

PubMed1978

The existence of an insoluble Z disc scaffold in chicken skeletal muscle.

Extraction of glycerinated chicken skeletal muscle with 0.6 M potassium iodide leaves a framework of insoluble components within each muscle fiber. This framework is composed primarily of planes of in-register Z discs that have been thickened by the accumulation of material on both sides of each disc during extraction. Membrane vesicles, presumably remnants of the T system, remain surrounding the Z discs. When the framework is sheared in a blender, it is preferentially cleaved between Z planes, resulting in the formation of large sheets of interconnected, closely packed Z discs in a honeycomb-like array. Cleavage occurs in regions formerly occupied by the A bands, which have been weakened by the removal of myosin. The existence and stability of these planar Z disc arrays demonstrate the presence and strength of connections between adjacent myofibrils. SDS-polyacrylamide gel electrophoresis reveals that this framework consists primarily of actin and desmin, with lesser amounts of a few proteins including alpha-actinin, myosin and tropomyosin. Z disc sheets and KI-extracted myofibrils provide a distinct face-on view and side view, respectively, of the Z disc. In indirect immunofluorescence, these two views have revealed that desmin is present at the periphery of each Z disc, forming a network of proteinaceous collars within the Z plane. alpha-Actinin is localized within each disc, giving a face-on fluorescence pattern that is complementary to that of desmin. Actin is present throughout the thickened Z plane, while myosin and tropomyosin exist only in the insoluble residue that coalesces on both faces of each disc. We conclude that desmin, perhaps in conjunction with actin, is responsible for interlinking Z discs of adjacent myofibrils, and may thus serve as a mechanical and structural integrator of muscle fibers. Its hydrophobic nature and coincident distribution with the T system suggest that it may also be responsible for mediating filament-membrane interactions and anchoring the triad to the Z disc. Its collar-like distribution suggests that it may aid in maintaining the structural integrity of the Z disc and the actin filaments inserted into it.

Actins↗

PubMed1991

Alterations in cardiac contractile proteins due to oxygen free radicals.

In view of the potential role of free radicals in the genesis of cardiac abnormalities under different pathophysiological conditions and the importance of contractile proteins in determining heart function, this study was undertaken to examine the effects of oxygen free radicals on the rat heart myofibrils. Xanthine plus xanthine oxidase (X + XO) which is known to generate superoxide anions (O2-) and hydrogen peroxide (H2O2), an activated species of oxygen, was found to decrease Ca(2+)-stimulated ATPase activity, increase Mg(2+)-ATPase activity and reduce sulfhydryl (SH) group contents in myofibrils; these effects were completely prevented by superoxide dismutase (SOD) plus catalase (CAT). Both H2O2 and hypochlorous acid (HOCl), an oxidant, produced actions on cardiac myofibrils similar to those observed by X + XO. The effects of H2O2 and HOCl were prevented by CAT and L-methionine, respectively. N-ethylmaleimide (NEM) and 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB), inhibitors of SH groups, also produced effects similar to those seen with X + XO. Dithiothreitol (DTT), a well known sulfhydryl-reducing agent, prevented the actions of X + XO, H2O2, HOCl, NEM and DTNB. These results suggest that marked changes in myofibrillar ATPase activities by different species of oxygen free radicals may be mediated by the oxidation of SH groups.

Animals↗