Immunoelectron microscopic changes of the platelet plasma membrane after activation

The observation of protein redistributions from one compartment to another during platelet activation reflects changes in platelet functionality. At rest alpha-granules express a high level of the main aggregation receptor GPIIb/IIIa, and only a small amount of the adhesion receptor complex GPIb/IX/V which lines the plasma membrane. After activation, the plasma membrane loses GPIb whereas the level of expression of the other aggregative proteins such as GPIIb/IIIa increase. These observations correlate well with the passage of the platelet from an adhesive to an aggregative state.