Interaction of plasma proteins with artificial surfaces: protein adsorption isotherms

A simple technique using a small disc which is dipped into a 125I-labeled protein solution has been devised to study the adsorption of human albumin, fibrinogen, and IgG onto Cuprophane or PVC. The purity of these human plasma proteins has been examined carefully with PAGE and immunochemical methods. The adsorption isotherms of albumin, fibrinogen, and IgG show a langmuir type adsorption. Delipidation of albumin did not alter the albumin affinity to Cuprophane and PVC. The surface saturation concentration (ng/cm2) for albumin, fibrinogen, or IgG were all found to be more on PVC (a hydrophobic surface) than on Cuprophane (a hydrophilic surface). The competitive adsorption of one protein species in a two- or three-protein mixture was also studied. Albumin and fibrinogen complete with each other for adsorption. The effects of IgG on the adsorption of albumin or fibrinogen were inconsistent and not predictable; the reason for this is unknown. The effect of laminar flow on albumin adsorption was studied with a specially designed Richardson flow chamber. In general caused an increase in albumin adsorption over that at static conditions. The increase of albumin adsorption was more pronounced also for PVC than for Cuprophane from 1 to 10 ml/min.

Affinity chromatographic demonstration of a thrombin binding protein from the platelet plasma membrane

Human platelet plasma membrane glycoprotein I with an apparent molecular weight of approximately 150,000 has been shown to be one of the proteins retained by thrombin immobilized on Sepharose 4B. The retained glycoprotein has been recovered by sodium dodecyl sulfate elution and characterized by SDS polyacrylamide gel electrophoresis in the presence of 2-mercaptoethanol.

A concise method for study of the binding of thrombin to human platelets

A rapid and sensitive technique is described for use in the study of the binding of 125I-thrombin to human platelets. The procedure involves the separation of free thrombin from platelet-bound thrombin by passage of this mixture through a discontinuous sucrose density gradient at low centrifugal force (1,500xg). Results obtained by this method are shown to be comparably to data obtained by two other conventional methods. This technique may facilitate further kinetic study of the binding of thrombin to human platelets.

The endothelium: roles in thrombosis and hemostasis

The renewed interest in endothelial function is based partly on success with tissue culture of endothelial cells. Endothelium functions primarily in the control of blood vessel wall permeability and in the provision of a blood-compatible lining surface. Recent findings indicate that endothelial cells are active metabolically in ways that may help prevent thrombosis. Endothelium actively degrades several different vasoactive compounds that circulate in blood and that can serve as platelet-aggregating agents. Endothelium also contains an inhibitor of platelet function and an activator of plasminogen, both of which can be released from the cell in response to appropriate stimuli. While intact endothelium functions primarily in prevention of thrombosis, damaged endothelium can contribute greatly to thrombus formation. Release of prostaglandins, adenine nucleotides, and other intracellular components from damaged endothelium can enhance platelet aggregation. Damaged endothelium may not function effectively in removal of vasoactive agents and may not release effective quantities of the inhibitor of platelet function or the activator of plasminogen. Altered endothelium exhibits tissue-factor activity, which can activate the extrinsic blood coagulation-system cascade. Finally, altered endothelial cells may contract and expose basement membrane to blood, thus enhancing thrombosis.

Multiple active forms of thrombin: binding to platelets and effects on platelet function

The effect of various forms of thrombin on certain platelet functions has been investigated. Partially purified bovine thrombin which is a mixture of multiple active forms of thrombin, was chromatographed to yield molecular species termed alpha-, beta-, and gamma-thrombin, each of which has varying degrees of fibrinogen clotting and esterase activities. A direct correlation was observed between the ability of the different forms of thrombin to clot fibrinogen and to influence platelet function. In general, thrombin with high fibrinogen clotting activity was also a potent inducer of platelet aggregation and the release reaction, while those species with low clotting ability were poor inducers of aggregation and release.

The subcellular distribution and partial characterization of cholinesterase activities of canine platelets

The multiple cholinesterase activities in canine platelets have been investigated. Platelets were homogenized by rapid decompression under nitrogen, glass tube/Teflon pestle, and glycerol lysis techniques. Rapid decompression under nitrogen technique was found to be the most efficient and gentle method for cell disruption. Homogenates were subfractionated using sodium diatrizoate density gradients. Marker enzyme assays and pulse labeling experiments with 5-hydroxyl[14C] tryptamine and [125I] thrombin on prepared subcellular fractions confirmed that the soluble, plasma membrane and the granule-1 fractions were all in reasonably pure form. Furthermore, labeling of the plasma membrane with [125I] thrombin is cited as the first successful attempt at attaining significantly bound marker for this structure. Cholinesterase activity distributions measured in these fractions indicated that about 30% of the activity was present in the plasma membrane, 50% in granule-1 and 5% in soluble fractions. Kinetic data of cholinesterase activities obtained from intact platelets, plasma membrane preparations and platelet release supernatants indicated that they are strikingly similar.

Adhesion of human blood platelets to glass polymer surfaces. II. Demonstration of the presence of a natural platelet adhesion inhibitor in plasma and serum

Adhesiveness of washed platelets resuspended in citrated plasma, serum, or several different media has been investigated. A method specific for quanititation of adhesion was used. Platelets suspended in saline of Tyrode's solution were found to be highly adhesive to glass, polyethylene, polyvinyl chloride, or Cuprophane. This adhesiveness of platelets to test surfaces decreased by nearly 50% when plasma was the suspension medium. When the suspension medium was serum, the decrease in adhesion was nearly 75%. Cohn fraction V also decreased the adhesiveness of platelets significantly, but highly purfied albumin had only a small effect. Several pharmacologic agents decreased platelet adhesiveness when added to platelets suspended in plasma or serum, but had negligible effect on the adhesiveness of platelets suspended in artificial media devoid of proteins. Normal washed platelets, when suspended in citrated plasma obtained from an afibrinogenemic donor or in normal serum, showed a significant decrease in adhesion compared to the same platelets suspended in normal citrated plasma. Addition of fibrinogen to afibrinogenemic plasma or normal serum restored the adhesiveness of platelets to normal levels. Normal platelets resuspended in plasma obtained from a thrombasthenic donor exhibited normal adhesiveness. These observations suggested that while fibrinogen promotes platelet adhesion, plasma or serum possess also an adhesion-inhibiting activity.