Synthesis of plasminogen activator by bovine corneal endothelial cells

Abstract

Plasminogen activator activity in purified cultured bovine corneal endothelial cells grown in tissue culture was demonstrated by a solid-phase assay based on the hydrolysis of [ 125I]fibrin. Plasminogen activation appears to take place on the surface of the corneal cells and not as a result of secretion of the activator. Only a small fraction of plasminogen activator, however, is associated with the membrane; 90% is located in the cytosol. As a result, after cell death or lysis, a large amount of plasminogen activator is released into the media. Plasminogen activator can be detected within 2 hr of adding plasminogen-containing serum to proliferating cells; fibrinolysis is maximal within 12 hr. The extent of fibrinolysis is dependent on the plasminogen concentration in the serum. Considerably more plasminogen activator is associated with endothelial cells derived from the cornea than with cells derived from bovine aorta. The clotting factor thrombin markedly inhibits corneal endothelial cell-mediated fibrinolysis. Since thrombin has no effect on the partially purified activator, inhibition must result from a direct effect on these cells. The ability to study the regulation of the synthesis and distribution of plasminogen activator by cultured corneal endothelial cells should aid in determining the normal physiology of fibrinolysis in the anterior chamber. In addition, this technique can be used to study fibrinolysis in other ocular tissues.