[Structural changes in the cytoskeletal actin in cultured muscle cells when the cultures are stimulated by polystyrene latex]. / Izmenenie struktury tsitoskeletnogo aktina v kul'tiviruemykh myshechnykh kletkakh pri stimuliatsii kul'tur polistirol'nym lateksom.

As we reported elsewhere, the addition of polysterol latex (180 nm) to chick muscle culture accelerated several myogenesis stages, such as proliferation and fusion. In the present work we tried to determine the role of cytoskeletal actin in the mechanism of acceleration. The localization of cytoskeletal actin was studied in normal and latex induced cultures with the help of rodamine--phalloidin. The obtained data have shown that latex beads added to the cultural medium brought about acceleration of cell spreading (the number of spread cell was approximately five times more in comparison with the norm) and enhanced the development of actin network (90% of the cell area was filled with stress-fibrils in 20 h, instead of within 1-3 in the norm). It is proposed that muscle cells interact primarily with latex beads in the cultural medium before seeding on the glass. From this point of view latex beads can be considered as a primary substratum. The cell contact with the primary substratum initiates the actin network reorganization that leads to activation of cell spreading with a subsequent acceleration of myogenesis process: adhesion, proliferation and fusion.

[The accelerating action of polystyrene latex on myoblast proliferation in culture]. / Uskoriaiushchee deistvie polistirol'nogo lateksa na proliferatsiiu mioblastov v kul'ture.

Latex beads (1800 A) added to chick embryonic muscle cell culture at the moment of plating accelerate and enhance the mitotic activity of myoblasts as soon as by the end of the first day of cultivation. The mitotic index of the induced cultures was several times greater than that characteristic of usual myoblast cultures. The formation of myotubes and the appearance of satellite-like cells was observed during the same period.

[A possible physico-chemical mechanism of cell fusion in skeletal muscle myogenesis by means of intercellular pinocytosis]. / Vozmozhnyi fiziko-khimicheskii mekhanizm sliianiia kletok v miogeneze skeletnoi myshtsy postredstvom mezhkletochnogo pinotsitoza.

The fusion mechanism of cells in myogenesis of skeletal muscle is proposed on the basis of capacity of forming intercellular contacts with pentalamellar structure to invaginate up to the formation of free vesicles, i.e. the intercellular pinocytosis. This process leads to a "loss" of the membrane material with the following perforation and rupture of the membrane at the site of cell contact. The formation of invaginations is connected with the clusterization of proteins on the cytoplasmic surface of plasmalemma, accompanied by an alteration of Gibbs' surface energy with the appearance of chemically induced and bending moments. The transition from the invagination to the vesicle depending on osmotic gradient of pressure between the fusing cells was estimated quantitatively. This gradient is determined by the mechanism of polymerization of protein subunits during the assembly of contractile elements in one of fusing cells.

[Ultrastructural characteristics of the pentalaminar contact and its role in myoblast fusion]. / Osobennosti ul'trastruktury piatisloinogo kontakta i ego rol' v sliianii mioblastov.

Two types of the pentalaminar structure were found in developing skeletal muscles. One of them is characterized by three electron-dense lines 23-25 nm in size. The other one, 11 nm in size, has only one electron-dense central line and forms membrane invaginations (blebs), 100-250 nm in diameter. The transformation of the "bridge" contact into the 2nd type pentalaminar structure and electron-dense bodies--"lenses" (60-65 nm) was established. The "lenses" contain an electron-dense material, similar to that of the "bridges". Neuraminidase hydrolysis shows that the "bridges" consist of glycoproteins. The muscle cells were extracted with 0.5% triton X-100. The detergent removes most of phospholipids. The first type of the pentalaminar structure remains stable to detergent treatment, whereas the second type may be dissolved. Besides, a partial destruction of surface membranes--"breaks"--are observed in the regions of membrane transmission to the pentalaminar structure. The detergent appears to act on those sites of the surface membrane which are instable and ready to fuse, especially on the bases of invaginations.

[Formation of intercellular contacts in myogenesis]. / Obrazovanie mezhkletochnykh kontaktov v miogeneze.

In myogenesis in vivo and in the muscle tissue culture certain intercellular junctions have been revealed; they differ in their ultrastructure and functions. For the stage of interaction between a myoblast with another myoblast contacts of adhesive type are distinctive: desmosomes and fasciae adherentes. They are necessary for adhesion of the cells with each other. Besides, gap and punctate contacts occur, serving for exchange of metabolites and electrical conjugation. At more advanced stages of fusion, when the myoblast gets into contact with the early muscle tubule, a bridge contact is observed, resembling the septal one, which is able to transform into a pentalayered (tight) junction. The latter type evidently participates in fusion of the membranes of the interacting cells.

[Intercellular interactions preceding muscle cell fusion]. / Mezhkletochnye vzaimodeistviia, predshestvuiushchie sliianiiu myshechnykh kletok.

Membrane interactions of myogenic cells of the 7-8 old chick embryos were investigated by electron microscopy. Tannic acid was used as specific fixative for biological membranes. Three types of specialized contacts can be revealed in fused myogenic cells: the first is like gap junctions, the second represents a pentalamellar structure, and the third is a so far non-described type of contact showing a membrane complex consisting of two parallel membranes arranged at a distance of approximately 15 nm and connected by electron-dense "bridges". The third type contact is revealed only by tannin-fixation. It is suggested that the "bridge" contact precedes the pentalamellar structure. A transition from the first type of contact to the second one is possible. The pentalamellar structure can be considered as an initial phase of fusion.

[Calcium localization in the degenerating myotubes of developing skeletal muscle in the chick embryo]. / Lokalizatsiia kal'tsiia v destruktivnykh miotrubkakh razvivaiushchikh skeletnykh myshts kurinogo émbriona.

Ca-accumulating formations found in degenerating myotubes of chick embryo by pyroantimonate technique have been identified as membrane bound bodies in the material fixed routinely for electron microscopy. These bodies seem to represent initial stages of a lipid degeneration of membranous structures. It is assumed that calcification of single degenerating subcellular structures may limit spreading necrosis over the whole cell.

[Calcium in the developing skeletal muscles of the chick embryo]. / Kal'tsii v razvivaiushchikhsia skeletnykh myshtsakh kurinogo émbriona.

The osmium-pyroantimonate technique was used for the ultrastructural study of Ca2+-localization in two types of chick embryo skeletal muscles: m. pectoralis and m. soleus. In 8- and 12-day old embryos the pyroantimonate precipitate was found on plasmalemma, condensed chromatine and ribosomes and in N-lines of I-band. During myogenesis (15-, 21-day old embryos) the calcium precipitate is redistributed from the above mentioned sites to terminal cisternae and N-line of I-band. It is proposed that calcium of N-lines may be involved in the glycogenolysis, its association with the muscle contraction occurring particularly at early developmental stages.

[Role of membrane structure in the formation of the myofibrillar system in myogenesis]. / O roli membrannykh struktur v formirovanii miofibrilliarnogo apparata v miogeneze.

The leading role of membranes in the formation of the myofibrillar system at different stages of chick embryo development (on the 8th, 12th, 15th day) was considered. At the early stages the myofibrillar assembly depends mainly on the plasma membrane (myofibrils are located beneath the sarcolemma) and later on it depends on the developing sarcoplasmic reticulum and T-system. It was shown that transverse tubules invaginating from the plasma membrane are the framework for the forming myofibrillar system, and thin filaments are attached to the transverse tubules at the sites of future Z-lines. These results support the idea that Z-lines originate from the membrane. Destruction of the membrane elements provokes disorganization of myofibrillar contractile material.

[Analysis of labeled leucine incorporation by nerve cells of a cultured spinal cord ganglion]. / Analiz vkliucheniia mechenogo leitsina nervnymi kletkami kul'tiviruemogo spinnomozgovogo gangliia.

The protein-synthesizing apparatus of sensitive neural cells was analysed in mature mammals at cultivation. Spinal cervical ganglia of mature rabbits were cultivated by the method of rotating tubes up to 4 days in a usual medium and in an amino-acid-enriched medium. The labelling level was defined radioautographically and by radioactivity of protein and acid-solving cell fractions registered by the scintillation methods. In order to obtain the fractions, Rose's method for dividing neural and glial cells in our modification was used. The glial neural cells were demonstated by our investigation to preserve their ability to incorporate the labelled leucine during any period of cultivation. The medium enriched with precursors of protein synthesis contributes to a more intensive incorporation of amino acid into protein and into the pool on the 4th day of cultivation, while the enriched medium sharply decreases radioactivity in the pool on the 1st day of cultivation. Intensity of the labelled leucine incorporation into the neurons drops towards the center of the explantat. The results obtained by the two methods coinside.

[RNA synthesis in mammalian nerve cells in vitro]. / Issledovanie sinteza RNK v nervnykh kletkakh mlekopitaiushchikh v usloviiakh in vitro.

Neurons of spinal ganglia of adult rabbits were cultivated during 4 days in rolling tubes, RNA synthesis of these neurons being determined by radioautography. In neurons of isolated ganglia, 1 hour following isolation, RNA synthesis was active and decreased up to 64% compared to the initial level only at the fourth day of cultivation. In small neurons, RNA synthesis was more active than in large ones. After addition of exogenous RNA precursors into the medium, the uptake of 3H-uridine increased, especially in large neurons.

[14C-leucine incorporation by the nerve and glial cells of a cultured spinal ganglion]. / Vkliuchenie 14C-leitsina nervnymi i glial'nymi kletkami kul'tiviruemogo spinal'nogo gangliia.

Spinal ganglia of adult rabbits were cultured in the routine and protein synthesis precursors-enriched media. On days I and 4 of cultivation, the intensity of 14C-leucine incorporation in protein and in acid soluble fraction of nerve and glial cells was determined. The tissue of the spinal ganglion keeps incorporating 14C-amino acid, into neurons and glia, for all the tested periods of cultivation with both the media employed. The curves of incorporation into the above fractions of nerve and glial cells cultured in the routine medium display similar patterns of changes, whereas those obtained from the enriched medium observations appear to be anti-fasic. The enrichment of the medium results also in less pronounced fluctuations in the intensity of the labeled amino acid in protein and 14C-leucine pool, on the tested periods of cultivation, which may provide more stable conditions of the explant's survival.