Development and ultrastructure of the neuromuscular junction in bronchial smooth muscle tissue

At various stages of pre- and postnatal ontogenesis ultrastructure of contacts of smooth myocytes and nervous terminals in the white mice bronchial wall has been investigated. Nervous fibers grow into the forming tissue of the lung beginning from the 11th day of embryogenesis. By the end of the prenatal development the nervous fibers fasciculi with varicosites and having vesicles are localized at the distance of 100-300 nm from the developing myocytes. Formation of dense neuromuscular junctions with the distance of 35-60 nm between the axonal membranes and the myocyte is observed on the 10-15 day after birth. In mature animals combination of various types of neuromuscular connections is revealed; they ensure local and distant neurotrophic regulation. In the bronchial smooth musculature afferent connections are revealed, as well as connections of myocytic processes with the effectors. Terminals of the cholinergic type predominate, adrenergic effectors occur very seldom. There are terminals, in which combination of vesicles having various structure and diameter are observed.     

Ultrastructure of the striated muscle tissue of the iris of birds]

Heteromorphism of the contractile elements of the iris muscular tissue in chick embryos and in chickens has been studied by means of electron microscopical investigation. The leading contractile tissue of the iris is the striated muscular tissue, which is formed as a cellular-simplastic system with its own cambium-myosatellitocytes. Some cells, containing myofilaments in their cytoplasm, are related to myofibroblastic and smooth muscle differons, which functions remain to be studied. A hypothesis is proposed on existence of two sources for development of the iris muscular elements. The first-stem cells for the striated muscular tissue; at early stages of embryonal development they are included into composition of ectomesenchyme of the neural crest and migrate into the area of the muscle anlages. The second-cells migrating from the ocular cup margins and developing into the smooth myocytes of the iris.     

Ultrastructural features of femoral artery myocytes during experimental leg lengthening

Femoral arteries in mature dogs have been studied electron microscopically at various stages of the shin lengthening performed after G. A. Ilizarov method. Certain ultrastructural signs demonstrating biosynthetic and secretory activation of myocytes directed to intensification of elastogenetic processes have been revealed. Immature elastic fibers are forming around myocytes as aggregations of microfibrils, later accumulations of amorphous material appear in them. On the 28th, 42d days of distraction, hyperproduction of intra- and extracellular vesicles is noted, as well as that of intracellular matrix. Cytoplasmic islets of myocytes and intercellular connections increase in number. In the subintimal layer, of the tunica media and at its border with adventitium, longitudinally situating fasciculi of smooth muscle cells are forming. The myocytic ultrastructural peculiarities noted, the new formations of elastic elements depend, at early stages of the experiment, on changes of regional hemodynamics, and at advanced stages - also on the effect of longitudinally acting tension stress.     

Differentiation of cells of the bronchial wall in the early period of embryonal development of the lungs]

Electron microscopical analysis of cellular elements of the developing lung has been performed during early stages of the prenatal development. The mesenchymal anlage of the organ is characterized with an essential cell polymorphism. The precursors of the smooth myocytes are formed on the 13th day of embryogenesis and they develop in a close contact with epithelial tubules. Synthesis and accumulation of contractile elements are determining signs of myoblasts differentiation. Already at first stages of differentiation they interact by means of specialized junctions of adhesive type and from clusters, situating on periphery of the epithelial tubules. Increase in amount of contractile filaments in cytoplasm of myoblasts is accompanied with formation of the basement membrane of these cells. Together with myoblasts in the mesenchyme, cells of fibroblastic differon at various levels of development are described.     

Structure and protein composition of sites of papillary muscle attachment to chordae tendineae in avian hearts

Summary Most cardiac myocytes transmit force across fasciae adherentes, specialized sites of cell-cell adhesion. However, some cardiac myocytes in papillary muscle terminate on collagenous connective tissue in the chordae tendineae. These papillary myotendinous junctions (MTJs) are specialized for force transmission from myocytes to extracellular matrix. In the present study, we compared structural molecules at papillary MTJs to those at fasciae adherentes and skeletal MTJs. By using indirect immunofluorescence, we found that papillary MTJs more closely resemble skeletal MTJs in their molecular composition in that they are enriched in talin, vinculin, integrin, and fibronectin. Zeugmatin and -actinin, both components of fasciae adherentes, are absent from papillary MTJs. Although papillary MTJs and skeletal MTJs display strong similarities in structural protein composition, ultrastructural organization of the two junctions is different. Papillary MTJs display little folding of the junctional membrane and, according to morphological criteria, more closely resemble sites of thin filament-membrane association in smooth muscle than skeletal MTJs. Thus, papillary MTJs display a combination of structural characteristics described previously in skeletal and smooth muscles but exhibit few structural features observed previously in cardiac fasciae adherentes.     

Myocytes of the inguinal lymph nodes

Owing to the method for making total plane preparations of the capsule after A. V. Borisov, it is possible not only to prove presence of myocytes in the capsule and in the trabeculae of the inguinal lymph nodes in the man and rat, but to open out general regularities of their distribution and orientation. In the capsule areas, corresponding to the places, where the lymph nodules are adjacent to (zone A), the number of myocytes is the least. They are oriented in various directions and are in close contact with each other (fascicular-reticulate principle of distribution of myocytes). In the capsule areas, surrounding A zones (named B zones) the myocytes are situated in tight layers and have circulatory orientation. At the place where the afferent lymphatic vessel gets into the capsule, precapsular lymphangion makes an infundibular dilatation and its myocytes along the sloping spiral get into the capsule, where they are arranged circulatory and form a muscular "constrictor". While studying ultrastructure of myocytes in the rat inguinal lymph nodes, it has been found out that their structure is typical for the smooth muscle cells. There are numerous myo-myocytic contacts of nexus type, that unite the myocytes of the node into a single functional complex.     

Ultrastructure and relations between cells in the myometrium and in myomas of the human uterus

The state of myocytes and their intercellular connections in an unaltered myometrium in the peripheral zone and in the central part of the myoma node has been studied electron microscopically. When analysing the peripheral zone of the uterine myoma, myocytes have resemblence with myometrial cells in the folliculine phase of the menstrual cycle. Simultaneously, certain changes are observed both in the intracellular components and in intercellular interrelations: myocytic nuclei swell, most part of chromatin is decondenced, cell cytoplasmic volume increases, in the prenuclear zone numerous agregates of ribosomes are revealed. The myocytes draw nearer and form specialized junctions, that ensure their cooperation.     

Peptidergic and monoaminergic innervation of the gonads in the holothurian Cucumaria japonica

In the holothurian gonad structure of the peptidergic and monoaminergic systems has been described. Axons of their cells form tissue and hemal terminals. Epithelial cells and smooth myocytes of the gonadal wall get direct innervation, having contacts with the axonal terminals that are separated by the cleft 50-75 nm in the diameter. It is possible that neuropeptides and biogenic monoamines are transported to the germ and follicular cells of the germinative gonadal zone via hemolymph of the hemal sinus.     

Ultrastructural study of specialized conducting and working myocytes in the sinoatrial region of the human heart. I. Qualitative analysis

A qualitative ultrastructural analysis of specialized conducting and working myocytes in the sinoatrial region of the human heart was made using autopsied and biopsied material from 45 men and women. Autopsied material was prepared not later as than 3 hours after the death. Biopsied material was taken during the operation for surgical correction of disturbances of cardiac rhythm and conduction. Cell contacts of light and dark myocytes within the sinus node, and of working myocytes of the right atrium were evaluated. The ratio of light to dark myocytes in the sinus node were estimated from both dead people and patients. The principles of correct ultrastructural classification of conducting and working myocytes in human heart are discussed.     

Changes in three-dimensional structure of the internal elastic membrane of rat aorta after its mechanical injury and regeneration

By means of scanning electron microscopy of chemically extracted preparations the dynamics of changes in the three-dimensional structure of the internal elastic membrane (IEM) of the rat aorta has been investigated after its lesion by a vascular clip. The mechanical lesion results in rupture of the IEM along external borders of the instrument lips and in crushing of its central part. A niche is formed, along its periphery it is surrounded with a practically intact IEM. The aorta regeneration is accompanied with neoelastogenesis. In the center of the niche newly formed elastic structures appear later, but the IEM reparation develops more actively. During the neoelastogenesis some stages are distinguished: at first separate elastic fibers appear, which then anastomosed, uniting into fasciculi and laminae. It is supposed that the IEM-restoration at regeneration depends on synthetic activity of smooth myocytes and on the other hand, the changes in the IEM structure can regulate their migration and metabolism.     

Some ultrastructural observations on the integument of a pentastomid

The cuticle of the cephalobaenid pentastomid Reighardia sternae is described at various stages of the moult-intermoult cycle. The intermoult cuticle comprises four layers: an outer epicuticle; an underlying dense layer, the protein epicuticle; a fibrillar endocuticle; and a denser subcuticle. The overall similarity between the structure and composition of these layers and those of insects is discussed. However, the orientation of the chitin-protein fibres in the endocuticle does not show the rotating structure characteristic of many arthropod species, but this does appear in the sclerotized hooks. It is suggested that this comparatively loose, poorly oriented endocuticular structure produces a highly extensible cuticle which is precisely adapted to the specialized, endoparasitic habit of this species. Events at ecdysis, particularly the secretion of moulting fluid and the deposition of cuticulin, follow the insect pattern precisely. The phyletic significance of these observations is discussed.     

Calcium-Induced Ultrastructural Interactions in Adrenocorticocytes

Steroidogenesis in adrenocorticocytes is closely related to intracellular [Ca²⁺]. To detect ultrastructural changes induced by growth in cytosolic [Ca²⁺], we used a rat adrenocortical cell culture, which was examined with electron microscopy and morphometric analysis. We established that either KCl-induced membrane depolarization evoking Ca²⁺ influx into the cell via voltage-operated Ca channels and Ca²⁺ ionophore, A23187, induced remarkable ultrastructural interactions between several cytosolic organelles. Lipid droplets known as key elements for Ca²⁺-induced steroidogenesis directly contacted with organelles containing the enzymes providing steroidogenic reactions (mitochondria, smooth and rough endoplasmic reticulum, nucleus, peroxisomes, and lysosomes). In most cases, the lipid droplets formed a specialized morphological structure at the sites of contact with the partner organelles. These structures are interpreted as a specialized transporting system, which provides contacts between organelles and exchange of intermediate products of the steroidogenesis process between the droplet and organelles.     

Morphology of the principal divisions of heart conducting system of rats]

Light optic and electron microscopic investigation of the sinuauricular node node (spu), atrioventricular node (pzhu) and bundle of His (pzhp) has been carried out in 23 hearts of intact non-inbred male rats. Original techniques of oriented embedding of elements of the conductive system for their electron microscopic identification have been suggested. A morphological classification of specialized cardiac myocytes has been worked out basing on differences in their form and size, number of myofibrils and degree of their regulation. On its base three type of specialized myofibrils have been revealed in the conductive system. Topography of these cells has been described within spu, pzhu and pzhp. The suggested ultrastructural classification of specialized cardiac myocytes is compared with the data obtained for the cardiac conductive system in other types of mammals.     

Lymph heart musculature in birds

Development and innervation of the lymph heart musculature of chicken, emu, rhea, and duck was studied by electron microscopy at post-hatch ages from 3 days to adulthood. Development of innervation was monitored by acetylcholinesterase staining. Horseradish peroxidase was used to determine the extent of the transverse tubule network. Chickens were unusual among these birds in that lymph heart myocytes had already undergone a definitive differentiation and degeneration by 3 days. In ducks and ratite birds, lymph heart myocytes more slowly but progressively differentiate a cytomorphology that does not conform in all characteristics to cardiac or skeletal muscle and even resembles in some aspects, smooth muscle. Myofibrils become the dominant cytoplasmic structure, transverse tubules form "internal couplings" with agranular reticulum cisternae, and "external couplings" are formed between myocytes at myomyal junctions. The myomyal junctions also contain AChE-positive reaction product and some subplasmalemmal vesicles that lack a dense core. The lymph heart myocardium of ducks of 2 weeks demonstrated mitotic figures. In adult ducks the myosatellite cell numbers diminish and a characteristic pattern of myocyte degeneration appears. In juvenile ducks and ratites some myocytes differentiate to conductile cells, much as the conductile myocytes and myofibers of the blood heart. The lymph heart innervation is described, and the role of nerve in differentiation and maintenance of myocyte morphology in the lymph heart is discussed.     

Intercellular space and nonsynaptic interneuronal connections of the mammalian brain

Electron-microscopic investigations of various parts of the CNS in laboratory mammals and man have demonstrated that a single cerebral intercellular space, presenting an immediate internal medium for the nervous tissue elements, has different structure at the border separating the media. Here is a complex of structures, included into composition of the hemato-encephalic and liquor-encephalic barrier. Data of the literature on chemical composition of the intercellular contents and on specific membranous receptors make it possible to suppose a communication role of the intercellular spaces, ensuring nonsynaptic intercellular connections and modulation of the synaptic transmission. At the level of membranes, that make walls of the intercellular clefts by means of certain phylogenetically ancient humoral mechanisms, interaction of systems of synaptic and nonsynaptic interneuronal connections is secured.     

Smooth muscle cells in the rat testicular capsule: a developmental study.

This study of the postnatal development (from 1 to 60 days) of smooth muscle elements in the rat testicular capsule has demonstrated that while such elements are identifiable by light microscopy at 30 days, myocytes are present at birth as seen by electron microscopy. The differentiation of smooth muscle from birth to 30 days has been described, by which time it is of adult morphology and content. Perhaps significantly, it is at 30 days that the testis achieves a scrotal position, although sexual maturity does not occur until about 60 days. Presumably, at 30 days the testicular capsule of the rat is capable of the spontaneous contractions which are known to occur in the adult and which are assumed to aid the transport of non-motile spermatozoa from the testis to the spididymis. The presence of occasional striated muscle fibers in the rat testicular capsule as reported previously has not been confirmed by this investigation, although their possible origin is discussed.     

The second EF-hand is responsible for the isoform-specific sorting of myosin essential light chain.

It has been known that isoforms of myosin essential light chain (LC) exhibit the isoform-specific sorting within cardiac myocytes and fibroblasts. In order to analyze which domain of LC is responsible for the sorting, various chimeric cDNA constructs between human nonmuscle isoform (LC3nm) and chicken fast skeletal muscle isoform (LC3f) were generated and expressed in cultured chicken cardiac myocytes. If chimeras contained LC3f sequence at the place that was restricted by BssHII and PstI, they were preferentially sorted to sarcomeres and precisely localized at A-bands, and their incorporation levels into the A-bands were identical with that of the wild type LC3f. However, other chimeras were distributed throughout the cytoplasm like the wild type LC3nm. Comparison of amino acid sequences revealed that 12 amino acids are different between chicken LC3f and human LC3nm in the BssHII-PstI fragment, and these amino acids are located within the second EF-hand of LC. These results indicated that the second EF-hand is responsible for the isoform-specific sorting of LC. Although the second EF-hand is not included in the key contacts with myosin heavy chain, it is supposed that this domain is important for the relative disposition of neighboring domains. Thus, the 12 amino acids in the second EF-hand might play a key role for modulation of overall configuration of LC, thereby influencing the precise association of the key contacts.     

Electrical, contractile, and ultrastructural properties of adult rat and guinea-pig ventricular myocytes in long-term primary cultures

The electrical, contractile, and morphological characteristics of ventricular myocytes isolated from adult rat and guinea-pig hearts and maintained in cultures for 7-24 days are described. These cultured cells form different networks, depending on the species, when plated at certain density and maintained under specific conditions; the cells within the networks appear to be electrically coupled. Their resting and action potentials, their contractile activity (shortenings), and their pharmacological responses qualitatively resemble those of freshly isolated myocytes. Cultured cells from both species exhibit near-normal ultrastructural organization of sarcomeres, myofilaments, and mitochondria, as well as formation of intercellular contacts, or gap junctions. These data indicate that cultured adult rat and guinea-pig myocardial cells that make intercellular contacts possess electrical, contractile, and ultrastructural properties and responses to pharmacological agents similar to those of the respective adult myocardial tissues and the functionally intact freshly isolated cells from which these cultures are prepared. Thus, this study indicates that long-term cultures (7-24 days) of networked cardiac myocytes could be used as a valuable experimental model in various investigations of excitation-contraction coupling in cardiac muscle.     

Proteolytic activity of specialized surface protrusions formed at rosette contact sites of transformed cells

Surface protrusions at the leading edge of a moving cell that make contact with the surrounding extracellular matrix (ECM) are its main motor for locomotion and invasion. Chicken embryonic fibroblasts transformed by Rous sarcoma virus (RSV-CEF) form specialized membrane rosette-shaped contact sites on planar substrata as shown by interference reflection microscopy (IRM). Such activity is lacking in normal cells. These rosette contacts are more labile than other adhesion sites, such as focal and close contacts. Ultrastructural studies demonstrate that rosettes are sites at which membrane protrusions from the ventral cell surface contact the substratum. These protrusions are filled with meshworks of microfilaments and contain the pp60src oncogene product, actin, vinculin, and alpha-actinin. However, unlike focal contacts, at the rosettes these proteins interact to extend a highly motile membrane. Rosettes have the biological activity of degrading ECM components, as demonstrated by (1) local degradation of fibronectin substrata at sites of rosette contacts, but not focal and close contacts; (2) localization of putative antiprotease antibody at sites of rosette contacts, but not at focal an close contacts; and (3) local disruption of fibronectin matrix at sites of protrusive activity seen by transmission electron microscopy (TEM). In addition, formation of the rosette contact is insensitive to the ionophore monensin, and to inhibitors of proteolytic enzymes, while local fibronectin degradation at rosette contacts is inhibited by inhibitors of metalloproteases, 1,10-phenanthroline and NP-20. I consider these membrane protrusions of the rosette contacts in RSV-transformed cells specialized structural entities--invadopodia--that are involved in the local degradation of the ECM.     

Autoradiographic and electron microscopic studies of minced cardiac muscle regeneration in the adult newt, notophthalmus viridescens.

The regenerative response of minced cardiac muscle grafts in the adult newt was studied using autoradiography and electron microscopy. One-sixteenth to one-eighth of the newt ventricle was amputated, minced, and returned to the wounded ventricle. At five days after grafting, no reorganization of graft msucle pieces was apparent and there was degeneration of much of the muscle graft. Another, smaller population of 5-day myocytes had euchromatic nuclei and intact sarcolemmae. In 10- and 16-day grafts, continuity between ventricular and graft lumina was established and coalescence of graft pieces was apparent. Ultrastructurally, 10- and 16-day graft myocytes appeared to have fewer myofibrillae and increased amounts of rough endoplasmic reticulum, polyribosomes, Golig complexes, and dense bodies when compared to uninjured ventricular myocytes. The peak of proliferative activity of graft cells was observed at 16 days. Electron microscopic autoradiography revealed breadkdown of myofibrillar structure in labeled myocytes, whereas in myocytes in the later stages of mitosis only scattered myofilaments and no Z bands were present. By 30 days, grafts appeared as an integrated structure composed primarily of cardiac muscle. Myocytes of 30-day grafts were observed in various stages of myofibrillogenesis and contained numberous 10-nm filaments. Seventy-day graft mycoytes had numberous well organized myofibrillae and intercellular junctions similar to those seen in uninjured ventricular myocytes.