Platelet density-dependent partition of platelet-von Willebrand factor between alpha granule and non-alpha granule...

In this study, we demonstrate that platelets contain a small but significant amount of platelet-von Willebrand factor (vWf) not associated with alpha-granules. When platelets free of plasma proteins are exposed to micromolar concentrations of digitonin, plasma membrane permeabilization occurs without disruption of platelet granules. Employing this technique, we have found that upon exposure of a total platelet population to 8 microM digitonin, 5% of total platelet-vWf is released into the supernatant; this occurs without release of beta-TG from alpha-granules. When platelets of discrete buoyant density profiles are tested, this extragranular platelet-vWf increased with decreasing platelet density. These findings suggest that a redistribution of platelet-vWf from alpha-granule to non-granule sites occurs coincident with a decrease in platelet buoyant density.