The pH dependence of quantitative ristocetin induced platelet aggregation: theoretical and practical implications - a new device for maintanance of platelet rich plasma pH

Abstract

Quantitative ristocetin induced platelet aggregation of normal platelet rich plasma (PRP) decreases with time after PRP preparation. An increase in pH of the PRP with time proved to be responsible for this finding. Diffusion of CO2 from the plasma is the prime determinant of the change in pH. Since a complex combination of factors influences CO2 diffusion (surface area to volume relationship, capping, mixing, etc.) the change in pH is variable with time. Thus, quantitative ristocetin aggregation should be pH controlled. A simple device for maintaining PRP pH constant by control of the ambient pCO2 was designed and found effective in keeping both pH and quantitative ristocetin aggregation constant over a prolonged period of time. It can be adapted for use in platelet aggregation studies employing other reagents. The pH dependence of ristocetin induced platelet aggregation is consistent with other data supporting an electrostatic interaction between the platelet, von Willebrand factor, and ristocetin. The authors favor a model wherein ristocetin neutralizes some of the platelet's negative charge and permits the von Willebrand factor to bridge sites on separate platelets to induce agglutination.