Adhesion of human platelets to collagen: evidence for two states of platelet activation.

Normal human platelets suspended in buffer were exposed to a suspension of bovine tendon collagen fibrils and the rate of adhesion observed over a period of 60 minutes. In fresh platelet preparations, approximately 15-20% of the platelets adhered within one minute, and the total percent adhesion, following pseudo first order kinetics after the first minute, approached 60% after 60 minutes. Pre-treatment with N-ethylmaleimide, dithiothreitol, and glutaraldehyde reduced adhesion at 1 minute to less than 5%, but only N-ethylmaleimide completely blocked adhesion at 60 minutes. Thus, freshly collected, washed human platelets contain two distinct subpopulations exhibiting greatly differing rates of adhesion, reflecting different levels of reactivity toward collagen.