Biophysical Journal 58: 299-307 (1990)
© 1990 the Biophysical Society

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Long-range interactions in mammalian platelet aggregation. I. Evidence from kinetic studies in brownian diffusion.

Department of Physiology, McGill University, Montreal, Quebec, Canada.

ABSTRACT

The Smoluchowski theory describing aggregation in suspensions of spherical colloidal particles due to Brownian diffusion-controlled two-body collisions, was used to obtain collision efficiencies, alpha B, for adenosine diphosphate (ADP)-induced platelet aggregation in citrated platelet-rich plasma (PRP) from humans, dogs, and rabbits. For these diffusion studies, PRP was stirred with 10 microM ADP for 0.5 s, then kept nonstirred at 37 degrees C for varying times before fixation; the percent aggregation was computed from the decrease in particle concentration with time measured with a resistive particle counter. Up to 20% of rabbit platelets formed microaggregates within 60 s of ADP addition to such nonstirred suspensions, corresponding to mean alpha B values of approximately 0.9. However, human and dog platelets aggregated approximately 10 times and 2-3 times faster than rabbit platelets within the first 60 s of ADP addition, corresponding to alpha B approximately 8 and 2, respectively. These high alpha B (much greater than 1) for human platelets were independent of initial platelet count and were equally observed with the calcium ionophore A23187 as activator. In about one-third of human, dog, or rabbit PRP, comparable and lower values of alpha B (less than 0.5) were obtained for a slower second phase of aggregation seen for the nonstirred PRP over 60-300 s post ADP-addition. Platelet aggregability in continually stirred PRP was distinct from that observed in Brownian diffusion (nonstirred) because comparable aggregation was observed for all three species' stirred PRP, whereas greater than 3-8 times more ADP is required to yield 50% of maximal rates of aggregation for nonstirred than for stirred PRP.(ABSTRACT TRUNCATED AT 250 WORDS)