Platelet Storage Results in a Redistribution of Glycoprotein lb Molecules

Platelet membrane glycoprotein (GP) Ib contains receptors for von Willebrand factor and thrombin. Its proteolytic fragment, glycocalicin, circulates in normal plasma. In this study, storage of platelet concentrates for 5 d resulted in a 221% increase in plasma glycocalicin (1.3 times the total amount of glycocalicin present on the surface of all platelets), an 8% overall increase in platelet surface GPIb, and the appearance of a surface GPIb-negative subpopulation of platelets. Total platelet GPIb content of fresh washed platelets, determined by gel electrophoresis and immunoassay of Triton X-100 lysates, averaged 159,740 molecules per platelet. There were 36,360 surface GPIb molecules per platelet, determined by immunoassay of the supernatant of fresh washed platelets whose surface GPIb had been completely plasmin-cleaved. In sumnpary, these studies provide evidence for (a) a redistribution of GPIb molecules with platelet storage, and (b) a large intraplatelet pool ofGPIb (approximately threefold larger than the platelet surface pool of GPIb).