Determination of platelet adhesion to collagen and the associated formation of phosphatidic acid and calcium mobilization

Abstract

A method was developed to study the adhesion of platelets to fibrillar collagen at 37°C in the absence of aggregation. Human platelets were labeled with [ 3H]-oleic acid, gel-filtered, and incubated with collagen in the presence of receptor antagonists to thromboxane A 2, 5-hydroxytryptamine, and platelet-activating factor, as well as a fibrinogen/fibronectin inhibitor and an ADP-removing system. Those platelets that adhered to collagen were separated from those that did not by filtration through a 10-μm nylon mesh and the extent of platelet adhesion was quantitated by determination of the radioactivity retained by the mesh. The extent of platelet adhesion was proportional to the amount of collagen added up to 100 μg/ml and was essentially complete by 1 min. At least 80–90% of the platelets were capable of adhering to collagen. Adhesion was potentiated by the presence of extracellular Mg 2+ and this potentiation was inhibited by extracellular Ca 2+. Phosphatidic acid increased markedly in those platelets that adhered to collagen and this was associated with increases in cytosolic free Ca 2+ levels that could be detected using the fluorescent Ca 2+ indicator fura-2.