Thrombin adsorption and possible relations to thrombus formation

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Abstract
In the circulation, adherent thrombi are most likely formed by nucleation and growth processes. The adsorption of an anchoring layer must be followed by further constituent interactions; these by crosslinking introduce cooperative effects which affect nucleation and growth rates. Adsorption of thrombin to nonpolar surfaces has been examined using a clotting time assay. Assay discrimination was determined by coefficients of variation: of the assay itself (0.6%), of reproducing diluted thrombin sources (0.37%) and of reproducing sets of dotting tubes containing fibrinogen (1.5%). Adsorptions are 0.54 mg/m2 at the solution–air interface, 0.77 mg/m2 at the solution–clean wall interface, and 0.04 mg/m2 to walls previously treated with thrombin. Average distance between thrombin molecules is 89 Å, the minimum adsorption energy is −11.7 kcal/mole and estimated thrombus adhesive strength 10kg/cm2. Thrombin can be the anchoring layer for a thrombus which contains thrombin, fibrin and platelets since all constituents interact with each other. The thrombin–fibrin intersection energy is about −7 kcal/mole. The platelet can, at least on interaction with thrombin, undergo structural changes which increase interaction. A variety of interactions and cooperative effects are possible. A problem is to develop protocols and assays which will permit specification of the anchoring layer and characteristics of subsequent interactions.

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