EDTA-induced increase in platelet surface charge associated with the loss of aggregability. Assessment by partition in aqueous two-phase polymer systems and electrophoretic mobility.

When human platelets in citrated plateletrich plasma (PRP) were incubated for up to 7 mm at 37#{176} C and pH 7.8 with EDTA, they progressively lost their ability to aggregate and, after separation from plasma, were found in progressively greater numbers in the upper phase of a two-phase dextranpolyethylene glycol system (i.e., had a higher partition coefficient). Partition values were also increased when the platelets were fixed in formalin after EDTA treatment. The increases were associated with increased anodal electrophoretic mobility. EDTA treatment of PRP at room temperature or pH 7.0 caused no change in platelet aggregability or partition coefficient, providing evidence that loss of aggregability is associated with the increased negative surface charge. Platelets from patients with thrombasthenia had normal partition coefficients, although they could not aggregate, and the coefficient usually increased normally after EDTA treatment. Gel-filtered platelets, free of most plasma proteins, also showed an increased partition coefficient after incubation with EDTA and fixation. The partition coefficient of control platelets differed depending on whether they were incubated with isotonic saline or with CaEDTA and whether they were fixed at room temperature or at 37#{176} C or in the presence of plasma.