[Structural changes in the cytoskeletal actin in cultured muscle cells when the cultures are stimulated by polystyrene latex].

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 accelerating action of polystyrene latex on myoblast proliferation in culture].

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].

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.

[Ultrastructural characteristics of the pentalaminar contact and its role in myoblast fusion].

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.

[Formation of intercellular contacts in myogenesis].

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.

[Intercellular interactions preceding muscle cell fusion].

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".

[Calcium localization in the degenerating myotubes of developing skeletal muscle in the chick embryo].

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].

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.

[Role of membrane structure in the formation of the myofibrillar system in myogenesis].

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.

[Analysis of labeled leucine incorporation by nerve cells of a cultured spinal cord ganglion].

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.

[RNA synthesis in mammalian nerve cells 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.

[14C-leucine incorporation by the nerve and glial cells of a cultured spinal ganglion].

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.