Vascular smooth muscle (VSM) cell migration and proliferation play a major role in the development of atherosclerotic lesions, graft occlusion, and restenosis after angioplasty. Cell migration implies the digestion of the surrounding extracellular matrix. Cell-associated proteolysis has been extensively studied in neoplastic and inflammatory cells, but very little is known about the proteolytic properties of VSM. We have evaluated the ability of rat cultured VSM cells to solubilize [3H]amino acid-labeled extracellular matrices produced by bovine VSM. When plated at a density of 30,000 cells per well in 24 multiwell plates, VSM cells were able to solubilize 63.3 +/- 7.0% of the extracellular matrix after 10 days in culture. Extracellular matrix digestion occurred also when the cells were cultured in plasminogen-depleted serum but was higher in the presence of 10 micrograms/ml purified plasminogen (net percent digestion after the subtraction of the appropriate control, 8.6 +/- 3.0% versus 21.2 +/- 3.5% after 3 days in culture, p less than 0.005, respectively). The involvement of other enzymes in addition to plasmin is confirmed by the ability of VSM cells to degrade extracellular matrices from which the plasmin-sensitive component was removed with plasmin pretreatment. Rat VSM cells were able to solubilize 52.3 +/- 2.0% of this residual extracellular matrix-associated radioactivity after 6 days in culture versus 26.1 +/- 1.5% in the control dishes (p less than 0.01, n = 5). Cell contact was required for extracellular matrix degradation: cell-conditioned medium did not have any effect on extracellular matrix digestion.(ABSTRACT TRUNCATED AT 250 WORDS)