Effect of cell density on thrombin binding to a specific site on bovine vascular endothelial cells.

Abstract

Thrombin binding to proliferating and confluent endothelial cells derived from bovine vascular endothelium were studied. [125I] Thrombin was incubated with nonconfluent or confluent endothelial cells and both the total amount bound and the amount linked in a 77,000 dalton thrombin-cell complex were determined. Approximately 230,000 molecules of thrombin bound per cell in nonconfluent cultures compared to 12,800 molecules per cell in confluent cultures. Approximately 67,000 thrombin molecules were bound in an apparently covalent complex, MW = 77,000 with each cell in sparse confluent cultures, whereas only 4600 thrombin molecules per cell were bound in this complex with cultures. Similar studies with [125I]thrombin and endothelial cells derived from bovine cornea revealed no difference either in the total amount of thrombin bound or in the amount bound in the 77,000 dalton complex using sparse or confluent cultures. When confluent vascular endothelial cultures were wounded, additional cellular binding sites for the 77,000 dalton complex with thrombin appeared within 24 h. A 237% increase in the amount of thrombin bound to these sites was induced by a wound which resulted in a 20% decrease in cell number in the monolayer. There was no significant increase in thrombin binding to other cellular sites at 24 h. The 1st change in thrombin binding after injury apparently is an increase in the cellular sites involved in the 77,000 dalton complex. Thrombin binding to endothelial cells may be important in the vascular response to injury.