Effect of activators and inhibitors on human blood platelets: study by freeze-fracturing technique and electron microscopy.

Samples of normal human platelet-rich plasma were activated by ADP (0.5 microM and 20 microM) or by cold treatment (4 degrees C). The effects of incubation in EDTA, colchicine or cytochalazin B were also studied. Samples were prepared by the freeze-fracturing technique and examined by electron microscopy. Faces of fractured membranes were examined for aggregation of particles, for pore-openings in the membrane, and for the general morphological appearance of the membrane-fractured faces. No aggregation of particles was found in platelet-rich plasma preparations treated with ADP, EDTA, colchicine or cytochalazin B, nor did the pore openings reveal any changes following these treatments. We conclude that platelet activation and an increase in microviscosity of the platelet membrane is not due to platelet aggregates in the membrane.