Subcellular fractionation and morphology of calf aortic smooth muscle cells: studies on whole aorta, aortic explants, and subcultures grown under

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Abstract
A comparative biochemical and morphological study was made of calf aortic smooth muscle cells found in situ and grown in vitro under various conditions. Striking alterations in enzyme contents, physical properties and morphological appearances of lysosomes, endoplasmic reticulum, plasma membranes and, to a lesser extent, mitochondria were observed on culturing of calf aortic smooth muscle cells. These changes first appeared in cells growing out of tissue explants. They developed further on subculturing of the cells and depended greatly on the culture conditions used. The alterations included increases in specific activities of some 5- to 25-fold of 4 acid hydrolases, an average 9-fold increase in 5''-nucleotidase, 7-fold increase in cytochrome oxidase and 4-fold increase in neutral .alpha.-glucosidase in subcultured smooth muscle cells compared to aortic cells in situ. Cell fractionation studies showed significant shifts in the equilibrium densities of plasma membranes, microsomes and lysosomes, but not of mitochondria, in smooth muscle cells growing from explants and in subcultured cells, compared to cells isolated from intact aortas. Although the cells grown in vitro exhibited typical phenotypic features of smooth muscle cells, such as abundant myofilaments and surface vesicles, alterations in the morphological appearance of the endoplasmic reticulum, Golgi apparatus and, especially, lysosomes were observed. Significant differences in specific cellular characteristics and functions of aortic smooth muscle cells grown in vitro compared to aortic cells in situ were demonstrated.