Study on the nature of starfish larval muscle cells in vitro

We describe a culture method in which larval muscle cells of the starfish Asterias amurensis develop from epithelial cells, probably deriving from the coelomic pouches. The nature of the muscle which appears in the culture is described morphologically, physiologically and ultrastructurally. Cells were dissociated from the late gastrula stage, treated with 0.6 M of glycine in half-strength sea water free of Ca²⁺ and Mg²⁺ for 12 hr, and cultured for various periods. Elongated cells appeared after about a week from small aggregates of epithelial cells which were found among the mesenchymal network on the 1st day of culture. The characteristics of the elongated cells are as follows: (1) they possess two or more arms; (2) they adhere to the cultural substratum, mesenchyme cells, and themselves at all parts of the cell body; (3) they contract in response to acetylcholine; (4) they contain an abundance of fibrous actin and myosin throughout their cytoplasm; (5) the cytoplasm contains bundles of thick (12-19 nm) and thin (5-8 nm) filaments without any dense material; and (6) no proliferative activity was observed while the cells were kept in culture for up to 14 days. These features were compared with those of the larval muscle cells in vivo.