Permanently proliferating rat vascular smooth muscle cell with maintained expression of smooth muscle characteristics, including actin of the vascular smooth muscle type.

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Abstract
Cells of an established clonal line (RVF-SMC) derived from rat vena cava are described by light microscopic and EM methods and biochemical analysis of the major proteins. The cells are flat, and moderately elongate and form monolayers. They are characterized by prominent cables of microfilament bundles decoratable with antibodies to actin and .alpha.-actinin. These bundles contain numerous densely stained bodies and are often flanked by typical rows of surface caveolae and vesicles. The cells are rich in intermediate-sized filaments of the vimentin type but do not show detectable amounts of desmin and cytokeratin filaments. Isoelectric focusing and protein chemical studies have revealed actin heterogeneity. In addition to the 2 cytoplasmic actins, .beta. and .gamma., common to proliferating cells, 2 smooth muscle-type actins (an acidic .alpha.-like and a .gamma.-like) are found. The major (.alpha.-type) vascular smooth muscle actin accounts for 28% of the total cellular actin. No skeletal muscle or cardiac muscle actin has been detected. The synthesis of large amounts of actin and vimentin and the presence of at least 3 actins, including .alpha.-like actin, were demonstrated by in vitro translation of isolated poly(A)+ mRNA. This my be the 1st case of expression of smooth muscle-type actin in a permanently growing cell. Permanent cell growth and proliferation are compatible with the maintained expression of several characteristic cell features of the differentiated vascular smooth muscle cell, including the formation of smooth muscle-type actin.