[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.