Interaction of plasmin with endothelial cells.

The interaction of proteases with endothelial cells is a key area in vascular biology. Prior research has shown that enzymes like thrombin and plasmin play roles in endothelial signaling and function. However, the specific mechanisms of plasmin binding and its functional implications remain unclear. Established knowledge includes the role of plasmin in fibrinolysis and its interactions with various cell types. This gap motivated a detailed investigation into plasmin's interaction with endothelial cells. No prior work had resolved the binding affinity or receptor specificity of plasmin in this context. The study aimed to clarify these points by examining binding dynamics and receptor involvement. The lack of clarity around plasmin's unique interaction with endothelial cells prompted this investigation. This paper addresses a specific question in protease-cell interaction research.

The aim of this study was to investigate how plasmin interacts with endothelial cells. Specifically, the researchers sought to determine the binding characteristics of plasmin to mini-pig aortic endothelial cells. The study focused on the time- and concentration-dependent nature of plasmin binding. The researchers also aimed to assess whether plasmin binding involves known functional sites on the enzyme. Another objective was to compare plasmin's binding with that of thrombin on the same cell type. The study sought to identify whether specific cell surface receptors mediate plasmin binding. The researchers also wanted to determine if plasmin binding affects arachidonic acid release. This investigation aimed to clarify the specificity of plasmin-endothelial interactions within the fibrinolytic system.

The study used a monolayer culture of mini-pig aortic endothelial cells. Human plasmin was labeled with 125I to track binding dynamics. Binding was assessed over time and at varying concentrations. Scatchard analysis was employed to determine binding site affinities. Chemical modification of plasmin was performed using phenylmethanesulphonyl fluoride and pyridoxal 5'-phosphate. The effects of these modifications on binding were evaluated. Neuraminidase and chondroitin ABC lyase were used to pretreat cells before binding experiments. The release of arachidonic acid from cell phospholipids was measured following plasmin exposure. These methods allowed the researchers to assess binding specificity and functional relevance.

Plasmin binding to endothelial cells was time- and concentration-dependent. Equilibrium between bound and free plasmin was reached within 90 seconds. Scatchard analysis revealed two binding site populations. High-affinity sites had a Kd of 1.4 X 10(-9) M and a density of 1.24 X 10(4) sites per cell. Low-affinity sites had a Kd of 2 X 10(-8) M and a density of 7.2 X 10(4) sites per cell. Bound plasmin was spontaneously released within 2 minutes. Chemical modification of plasmin did not affect binding, suggesting non-active site involvement. Plasmin and thrombin did not compete for binding sites on endothelial cells. Pretreatment with neuraminidase or chondroitin ABC lyase reduced binding by 50%.

The interaction of plasmin with endothelial cells is specific and rapid. Binding occurs via high- and low-affinity sites, with no evidence of active site involvement. Plasmin binding is distinct from thrombin binding, indicating separate receptor systems. Chemical modification experiments suggest that neither the active center nor the heparin-binding site is essential for plasmin binding. The study found no significant effect of plasmin on prostacyclin formation. Neuraminidase and chondroitin ABC lyase pretreatment reduced binding, suggesting glycosaminoglycan involvement. The results highlight the specificity of plasmin in the fibrinolytic system. Plasminogen did not bind to endothelial cells under the same conditions as plasmin.