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 the expression of platelet-von Willbrand factor on platelets under conditions in which glycolysis and/or oxidative phosphorylation were inhibited. We found that platelet-vWf expression on the surfaces of both unstimulated and stimulated platelets required energy and was maximally decreased when metabolic ATP was maximally depleted. Platelet-vWf expression correlated directly with estimates of adenylate energy charge in both unstimulated and stimulated platelets. In addition, platelet shape 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 platelet-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 effect changes in platelet shape is less than that necessary to maintain basal 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 expression.