Comparative studies of the fibrinolytic activity of cultured vascular cells

Abstract

The fibrinolytic components in cultured endothelial cells (ECs) were examined and compared to those in non-endothelial vascular cells (NEVCs) and in normal and virally-transformed fibroblasts. All vascular cells exhibited plasminogen activator (PA) activity. This activity was low in ECs isolated from rabbit aorta and vena cava but high in NEVCs isolated from these same tissues, indicating that the fibrinolytic potential of the vasculature is not restricted to the endothelium. Low PA activity was also characteristic of ECs obtained from human umbilical cord vein. In contrast, both ECs and NEVCs isolated from bovine aorta and vena cava had high PA activity and were even more active in this respect than chick embryo fibroblast transformed by Rous sarcoma virus. Treatment of all cells with 5 × 10 −8 M phorbol myristate acetate, a tumor promoting agent, resulted in a variable but significant stimulation of PA activity. The low PA activity associated with some of the EC cultures correlated with the presence of a cellular inhibitor of fibrinolysis. Inhibitor activity was high in rabbit and human ECs and low in rabbit NEVCs and in chick embryo fibroblasts. No inhibitor activity could be detected in cultures of confluent bovine aortic ECs although there was significant inhibitor activity associated with sparsely populated cultures. The specific activity of PA in ECs also fluctuated with cell density, increasing approximately 20-fold as sparsely plated cells grew to confluency. These observations emphasize 1) that tissue associated fibrinolytic activity represents a balance between the activities of PAs and cellular inhibitors, 2) that the relation between PA and inhibitor may change with the growth state of the cells, and 3) that these activities vary with species of origin and thus are not necessarily indicative of any specific cell type.