RAPID COMMUNICATION Differential Redistribution of Platelet Glycoproteins Ib and IIb-IIIa After Plasmin Stimulation

The subcellullar localization of the platelet membrane receptors glycoproteins (GP) Ib and Ilb/lla has been studied within resting platelets by a combination of biochemical and cytochemical techniques. While both GPlb and GPllb/llla are localized within the plasma membrane and surface-connected canalicular system (SCCS) membranes, only GPIIb/ llla is present within the internal face of a-granular membranes. Previous studies demonstrated that plasmin can induce platelet stimulation and also decrease ristocetininduced platelet aggregation; it was suggested that this was because of GPlb degradation by plasmin. In this study, the respective localizations of both GPlb and GPllb/llla were visualized during in vitro plasmin stimulation of platelets. Generally, plasmin induced shape change, pseudopod formation, organelle centralization either with or without a-granule release depending on the conditions of stimulation. Plasmin treatment of platelets at 37°C resulted in the disappearance of GPlb from the cell surface and its subsequent redistribu-