The distribution of concanavalin A- and cationized ferritin-binding sites on plasma membrane of human platelet and the changes of these sites in cells responding to adenosine diphosphate.

Investigations were carried out to study the distribution of the concanavalin A- and cationized ferritin-binding sites on the plasma membrane of human platelets and to ascertain the changes of these sites in cells stimulated with adenosine diphosphate (ADP) with time as well. The concanavalin A-binding sites of the unwashed fixed platelets were sparsely distributed on the plasma membrane at a distance of up to 80 nm from the outer leaflet of the plasma membrane. The washed unfixed platelets, however, showed a dense distribution within a range of 70 nm from the outer leaflet of the plasma membrane. Changes in the distribution of concanavalin A-binding sites on the plasma membrane of platelets stimulated with ADP were characterized by a marked increase in the number of binding sites and by protrusion up to a distance of 150 nm from the outer leaflet of the plasma membrane 1 minute after the reaction had occurred. The concanavalin-A binding sites may be semicryptic in view of the fact that they were exposed by washing or protruded as a result of the stimulation with ADP. The cationized ferritin binding sites were uniformly distributed with high density on the plasma membrane of the unwashed fixed platelets. In washed unfixed platelets, however, they were sparsely distributed with cluster formation. It is suggested that the glutaraldehyde fixation itself has an effect on the binding of the cationized ferritin particles on the plasma membrane of platelets. The various changes in the concanavalin A-binding sites appearing 1 minute after the reaction with ADP may represent morphological evidence indicating that the platelets have acquired adhesiveness.