Distinction between smooth muscle, fibroblasts and endothelial cells in culture by the use of fluoresceinated antibodies against smooth muscle actin.

FITC-labelled antibodies against native actin from chicken gizzard smooth muscle (Gröschel-Stewart et al., 1976) have been used to stain cultures of guinea-pig vas deferens and taenia coli, rabbit thoracic aorta, rat ventricle and chick skeletal muscle. The I-band of myofibrils of cardiac muscle cells and skeletal muscle myotubes stains intensely. In isolated smooth muscle cells, the staining is located exclusively on long, straight, non-interrupted fibrils which almost fill the cell. Smooth muscle cells which have undergone morphological "dedifferentiation" to resemble fibroblasts with both phase-contrast microscopy and electronmicroscopy still stain intensely with the actin antibody. In those muscle cultures which contain some fibroblasts or endothelial cells, the non-muscle cells are not stained with the actin antibody even when the reactions are carried out at 37 degrees C for 1 h or after glycerination. Prefusion skeletal muscle myoblasts also do not stain with this antibody. It is concluded that the actin antibody described in this report is directed against a particular sequence of amino acids in muscle actin which is not homologous with non-muscle actin. The usefulness of this antibody in determining the origin of cells in certain pathological conditions such as atherosclerosis is discussed.