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.     

Molecular mechanisms of regulation of the contractile apparatus of smooth muscles]

This review describes the main ultrastructural features, molecular organization and regulation of smooth muscle contractile machinery. Possible molecular mechanisms of smooth muscle sensitization to Ca2+, Ca(2+)-independent contraction and latch state are discussed.     

Further observations concerning the motor innervation of the tensor tympani muscle of the cat

The cat tensor tympani muscle presented an uncommon ultrastructural organization of neuromuscular junctions compared with those in the other striated muscles. In cross sections, individual neuromuscular junctions had very extended contact area of the nerve terminal and muscle fiber, the terminal bouton was covering as a "calyx" the postjunctional muscle fiber. Long basal lamina was interposed between them. The sarcolemma at the level of the nerve terminal had multiple infoldings along its length, or smooth postjunctional muscle membrane was found beneath endings on both fiber types.     

Variable patterns of actin filaments in mammalian skeletal muscle

Summary The ultrastructural organization of myofilaments in skeletal muscle was studied in four mammalian species (mouse, rat, hamster, goat). In all these species, myofibrils showing irregularly distributed arrays of a variable number of actin filaments (from 6 to 11) were observed. The proportion of such myofibrils and the predominant patterns of actin filaments varied from one species to another. These results are in agreement with those previously reported for human skeletal muscle.     

Body wall organization in enchytraeids

The muscle organization of the body wall in some species of oligochaetes belonging to the Enchytraeus genus is described. No differences have been detected in their circular muscles, whereas longitudinal muscles show significant differences, allowing an easy identification of the various worm species. In particular, differences are noticeable in the external longitudinal layer. These observations suggest that structural and ultrastructural muscle fiber organizations can be used as a taxonomic tool.     

Restoration of dysgenic murine (mdg) myotube contraction after addition of Schwann cells from normal mice in vitro

Muscular dysgenesis in mutant mice is characterised by failure of excitation-contraction (E-C) coupling and consequent loss of skeletal muscle contraction. Contractile activity is restored in vitro by the addition of normal mice cells (11) (18) (7). In the present study we show a new model: contraction and ultrastructural organization of dysgenic myotubes are restored by coculture with Schwann cells from normal mice.     

3-dimensional ultrastructural characteristics of the cardiomyocytes of SHR strain rats with spontaneous genetic hypertension

The quantitative morphological analysis of hypertrophied cardiomyocytes was carried out in SHR rats (spontaneously hypertensive rats). The features of spatial ultrastructural organization of heart muscle cells were shown as manifested in the increased synthesis of contractile proteins and focal disorders of myofilament arrangement. Stereological analysis revealed the decrease of the ratio of the summary volume of the main cardiomyocyte organelles (mitochondria, smooth sarcoplasmic reticulum and T-system) to the myofibril volume.     

Abnormal transverse tubule system and abnormal amount of receptors for Ca2+ channel inhibitors of the dihydropyridine family in skeletal muscle from mice with embryonic muscular dysgenesis

We have found two important sets of abnormalities in skeletal muscle from mice with embryonic muscular dysgenesis. These abnormalities involve the internal structural organization of the muscle fiber and its content of voltage-dependent Ca2+ channels. The first abnormality concerns the ultrastructural aspects of the membranous couplings between sarcoplasmic reticulum and the transverse tubules, known as triads. The triads are less numerous, are disorganized, and lack spaced densities (feet). The second abnormality is a significant decrease in specific binding sites for the dihydropyridine derivatives, (known as Ca2+ channel inhibitors) in striated skeletal muscle, but not in cardiac muscle. Both sets of abnormalities are potentially directly linked to the uncoupling of excitation and contraction.     

Glomus tumor cells: evaluation of smooth muscle and endothelial cell properties

Six cases of glomus tumor in superficial soft tissues were investigated immunohistochemically for the presence of different types of intermediate filaments, myosin, laminin, a basal lamina glycoprotein, and the endothelial cell markers, factor VIII-related antigen (FVIIIR:Ag) and Ulex europaeus I lectin (UEA I) binding sites. The tumor cells appeared to contain only vimentin, the fibroblast-type of intermediate filament protein. They were also positive for myosin, and were invested by laminin-positive basal lamina-like material, but did not express endothelial cell markers. Ultrastructural studies revealed prominent arrays of both intermediate filaments and microfilaments, the latter resembling the myofilament bundles seen in smooth muscle cells. The results show that glomus tumor cells resemble smooth muscle cells in their content of myosin and in some ultrastructural features. In their lack of desmin, however, they differ from most types of smooth muscle cell, although they are similar in this respect to some vascular smooth muscle cells.     

Organization of native and in vitro-reassembled myosin filaments from lobster tonic muscle

Tonic muscle of the crusher claw of the American lobster (Homarus amencanus) was investigated with respect to sarcomeric organization and the capacity for self-assembly of extracted myosin for comparison with the same properties of rabbit muscle. Native myosin filaments in the lobster muscle are much longer than in rabbit skeletal fibers, and differ further in sarcomeric organization in showing an actinto-myosin relationship in which two actin filaments are shared between adjacent myosins in a 12-membered orbital. The self-assembly of lobster myosin into filaments comparable in length and fine structure to the natural filament was achieved in the presence of excess Mg²⁺, a condition not required for rabbit myosin self-assembly. Results of in situ and self-assembly studies indicate a difference in molecular organization between lobster and rabbit myosin filaments and of the inferred presence of regulatory factors in the formation of these ultrastructural elements. These studies represent the groundwork for an investigation of in vitro polymerization of actin in association with the synthetic lobster myosin filament.     

The respiratory system in Arctocephalus australis (Pinnipedia, Otariidae). I--Macroanatomy and microanatomy of the trachea and extrapulmonary airways]

This paper presents the results of histological and histochemical organization of trachea and primary bronchi. The presence of a subepithelial lamina and a smooth muscle layer in the superficial corion, probably related with a functional respiratory mechanism are defined. The structure of tracheal and primary bronchi glands, the way they secretes and the type of secretion are also described.     

Correlation between nerve terminal size and muscle fibers diameter in urodela extrinsic eye muscle.

Extrinsic eye muscles of newts and salamanders were investigated by means of electron microscope. It was possible to distinguish two types of muscle fiber tonic-slow and twitch-fast acting ones. It was shown that mioneural junctions in both types of fibers differ in their ultrastructural organization because of lack of post-synaptic infoldings on the surface of slow tonic fibers. After "cholinesterase" "staining" it was possible to measure the surface of junctional area and correlate it with the diameter of particular muscle fiber. The results show a positive correlation.     

Comparative ultrastructure of Mycobacterium leprae and Mycobacterium lepraemurium cell envelopes.

The structural properties of the cell envelopes of Mycobacterium leprae and Mycobacterium lepraemurium were investigated by freeze-fracture, freeze-etching, and negative-staining techniques. Freeze-fracture split the cell wall and exposed the internal features of the peptidoglycolipid mycosidic filamentous network. The cell membrane was also split into two asymmetric faces. The external fracture face was characterized by linear arrays of intramembranous particles, whereas the protoplasmic fracture face showed randomly distributed clusters of particulate entities. Comparative analysis of the ultrastructural features observed in M. leprae and M. lepraemurium indicated that the organization of the cell envelope in these two species differed particularly with respect to the amount and complexity of the superficial peptidoglycolipid and mycosidic integument, which is poorly developed in the mycobacterium responsible for human disease.     

The larval development of lateral musculature in gilthead sea bream Sparus aurata and sea bass Dicentrarchus labrax

Fibre-type differentiation of the lateral musculature has been studied in Sparus aurata (L.) and Dicentrarchus labrax (L.) during larval development. Histochemical and ultrastructural techniques show two presumptive muscle layers and two germinative zones of presumptive myoblasts. At hatching, myotomal muscle consists of a monolayer of thin undifferentiated cells near the skin (first germinative zone) overlying another mono-layer of small diameter fibres extending hypaxially and epaxially away from the transverse septum. Below this, there is a much thicker, deep layer of fibres, generally large in diameter and polygonal in shape. The presumptive myoblasts are located between these two layers of fibres in the second germinative zone. Initially, the superficial and deep muscle fibres show high and low myosin ATPase activity, respectively. Both layers grow by generating new fibres from the two mentioned germinative zones. At the end of larval life, the superficial layer changes its histochemical profile from high to low myosin ATPase activity and, at the same time, intermediate or pink muscle fibres can be observed by oxidative activity (the NADH-TR reaction). Morphometric analysis shows a significant increase in mean fibre diameter during successive ages, as shown by the Student's t-test (hypertrophic growth). Skewness and kurtosis values of fibre diameters point to the generation of a new fibre population from the germinative zones (hyperplastic growth).     

Immunogold EM reveals a close association of plectin and the desmin cytoskeleton in human skeletal muscle.

Plectin is a multifunctional cytoskeletal linker protein with an intermediate filament-binding site and sequence elements with high homology to actin-binding domains. Mutations of the human plectin gene as well as the targeted inactivation of its murine analog cause a generalized blistering skin disorder and muscular dystrophy, thus implying its essential role in cells that are exposed to mechanical stress. In the present study we report the characterization of two new domain-specific plectin antibodies as well as ultrastructural localization of plectin in normal human skeletal muscle. Using immunogold electron microscopy, we localized plectin at three prominent sites: 1) Plectin is found at regularly spaced intervals along the cytoplasmic face of the plasma membrane. 2) It is distinctly localized at filamentous bridges between Z-lines of peripheral myofibrils and the sarcolemma and 3) at structures forming the intermyofibrillar scaffold. At the latter two locations, plectin and desmin were found to colocalize. Our ultrastructural analysis suggests that plectin may have a central role in the structural and functional organization of the intermediate filament cytoskeleton in mature human skeletal muscle.     

Comparative aspects of cardiac and skeletal muscle sarcoplasmic reticulum.

While differing in numerous physiological and biochemical parameters, mammalian cardiac and skeletal muscles exhibit many common ultrastructural characteristics. General subcellular organization is similar with longitudinal disposition and organization of the myofibrils as well as subcellular organelles such as mitochondria, sarcoplasmic reticulum and transverse tubules. Significant differences are more readily discerned in terms of degree, not only with respect to relative amounts of various organelles, but also in regard to membrane composition. It is these macromolecular variations in membrane components which may, at least in part, provide the basis for differences in overall functional characteristics in the muscles.In cardiac, as well as skeletal muscle, the concentration of Ca²⁺ ions at specific intracellular sites regulates the contractile state of the muscle. The differences in mechanism and sources of Ca²⁺ for contraction in cardiac and skeletal muscle are but a few of the unsolved areas which are now being addressed. We shall focus primarily on research advances involving cardiac and skeletal SR emphasizing the contrasting features related to their functional roles in control of contraction and metabolic events.     

Localization and organization of microfilaments and related proteins in normal and virus-transformed cells

The localization and organization of actin-like microfilaments in normal, SV-40 and adenovirus transformed cells are determined by the coordinated use of light optical, electron optical and biochemical techniques. In adenovirus-type 5 transformed hamster embryo cells, microfilament meshworks appear to be the predominant organizational form of cellular actin, while in normal hamster cells, microfilament bundles are prevalent. Differences between 3T3 and SV-40 transformed 3T3 cells are less apparent and may be related to the packing and intracellular distribution of microfilament bundles. Attempts at relating these ultrastructural changes in transformed cells to the images obtained following reaction with fluorescein-labelled myosin fragments and indirect immunofluorescence with smooth muscle myosin antibody are discussed. In several instances the fluorescence microscope images do not correspond to the ultrastructural observations. The results are discussed in terms of the possible relationships between alterations in cytoplasmic contractile elements and the abnormal behavior of transformed cells.     

Intermediate filaments in the giant muscle cells of the nematode Ascaris lumbricoides; abundance and three-dimensional complexity of arrangements

The body muscle cells of the nematode Ascaris lumbricoides are characterized by massive amounts of intermediate filaments (IF). These occur in all three regions of this giant cell type. They traverse the cytoplasm of the balloon-like belly, which houses the nucleus, and occur as bundles in the arm-like extensions to the nerve. The organization of IF in the third region, the contractile fiber, was analyzed further by serial sections and three-dimensional reconstruction. IF bundles traverse the glycogen-rich lumina of the fiber and reach as baskets around the sarcomeres. Together with numerous dense bodies they form the Z-band-like arrangements. IF bundles reach the plasma membrane at hemidesmosome-like specializations often situated at deep membrane invaginations filled with a fibrillar component of the extracellular matrix. The ultrastructural appearance of IF bundles is connected to the contractional state of the sarcomeres. They appear straight in extended muscle but coil up upon contraction. In the pharynx massive IF bundles are oriented longitudinally. A second type of IF bundles follows the radially oriented sarcomeres. These reveal pronounced Z-band type structures with massive disks. IF surround the sarcomeres and seem to terminate at these disks. We discuss possible functions of the complex IF organization in body muscle and pharynx.     

An Ultrastructural Study of Lentomonas applanatum (Preisig) N. G. (Euglenida)

ABSTRACT. Lentomonas applanatum (syn. Entosiphon applanatum Preisig) is a biflagellate, phagotrophic euglenid found in intertidal salt marshes. Lentomonas applanatum bears a superficial similarity to Entosiphon sulcatum , however, an ultrastructural study of L. applanatum revealed many features that are atypical for other described species of the genus Entosiphon . These features include number and organization of pellicular strips, construction of the feeding apparatus, nature of the flagellar transition zone and flagellar apparatus, and point of flagellar emergence. These differences show that L. applanatum is related more closely to phagotrophic genera such as Ploeotia than to E. sulcatum . The construction of the feeding apparatus and pellicle suggest that L. applanatum has retained many of the pleisiomorphic characters that were present in the earliest euglenids. The presence of similar structures in other related protists may provide important clues as to the evolution of the Euglenida.