ENERGY-DEPENDENT EXPRESSION OF PLATELET-VON-WILLEBRAND FACTOR ON THE SURFACE OF UNSTIMULATED AND STIMULATED PLATELETS

We have studied the energy requirements (adenosine triphosphate) for t he expression of platelet-van Willbrand factor on platelets under cond itions In which glycolysis and/or oxidative phosphorylation were inhib ited. We found that platelet-vWf expression on the surfaces of both un stimulated and stimulated platelets required energy and was maximally decreased when metabolic ATP was maximally depleted. Platelet-vWf expr ession correlated directly with estimates of adenylate energy charge i n both unstimulated and stimulated platelets. In addition, platelet sh ape change and agonist-induced intracellular Ca2+ flux were maintained at lower AECs than were either platelet aggregation or alpha-granule secretion. Our results indicate that the surface expression of platele t-vWf on unstimulated platelets is a dynamic process, and that energy is required to maintain basal amounts of platelet-vWf on the platelet surface. Our data also suggest that the metabolic ATP required to effe ct changes in platelet shape is less than that necessary to maintain b asal platelet-vWf surface expression or to produce full alpha-granule secretion. We show that platelet-shape change in the absence of alpha- granule secretion can result in an increase in platelet-vWf surface ex pression.