Ultrastructural studies of a polygonal myofilament network in cultured rat aortic smooth muscle cells

Cultured rat aortic smooth muscle cells (SMC) were examined by electron microscopy and found to contain polygonal networks of 75 A degrees thin myofilament bundles. The cells also had large bundles of longitudinally aligned thin myofilaments with periodically spaced dense bodies. Abundant plasmalemmal vesicles were present at the cell periphery, and the cells were connected by desmosomes. Intercellular spaces contained sparse amounts of elastic fibers, a material generally present in SMC cultures. Analyses of amino acids by automated column-chromatography showed that isodesmosine and desmosine, two amino acid residues unique for elastin, were present. Accordingly, it was concluded that polygonal networks, previously detected solely in cultured nonmuscle cells, were present in SMC. Other findings suggest 1) a change in myofilament arrangement takes place during cell migration, and 2) rat aortic SMC grown in tissue culture flasks is an important experimental tool in the study of cell motility since such myofilament rearrangements were observed to occur up to fourteen days in first passage.