Electrochemical features of platelet interactions

Abstract

Platelets participate in hemostasis and thrombus formation. The physicochemical basis at the molecular level for platelet adhesion, cohesion to form aggregates and the resultant viscous metamorphosis is not well understood. Under physiological conditions, blood platelets possess a net negative charge and decreases or changes in this charge have been implicated in both their adhesion and aggregation. The peripheral zone of the platelet contains glycoproteins and glycolipids. A variety of charged groups are present including positively charged amino groups and at least three types of negatively charged groups. The carboxyl group of terminal sialic acid residues is considered to be a major contributor to the negative charge of platelets. Removal of as little as 10 percent of the peripheral zone sialic acid by neuraminidase results in a shortened platelet lifespan in vivo . The electrokinetic properties of blood platelets are changed by interaction with a great variety of agents. In those cases where specific adsorption occurs it is possible to study the relationship between adsorption, change in surface charge, and the process of aggregation. It should be noted that in physiological media only those charge groups within about 8 Å of the electrophoretic surface of the platelet will contribute to a significant extent to the electrophoretic properties. The electrophoretic mobility of platelets has been determined for a variety of animal species and in humans for a wide spectrum of disease situations. The measurement of platelet electrophoretic mobilities before and after treatment with adenosine diphosphate and norepinephrine has been introduced as a test of platelet function. However, so many variables may influence the surface properties of blood platelets including method of preparation, time, temperature, pH, contact phenomena, shear conditions, ionic strength and composition of suspending media, conditions for mobility measurements, etc., that considerable apparent disagreement exists in the literature regarding platelet electrokinetics.