Long-range interactions in mammalian platelet aggregation. I. Evidence from kinetic studies in brownian diffusion.
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. The above results point to the existence of long-range interactions mediating platelet aggregation in Brownian diffusion-controlled platelet collisions which varies according to human > dog > rabbit platelets. The roles for platelet pseudopods and adhesive sites in these long-range interactions are presented in part 2.
Department of Physiology, McGill University, Montreal, Quebec, Canada.
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D000244:Adenosine Diphosphate / Q000494:pharmacology; D000328:Adult; D000818:Animals; D001792:Blood Platelets / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D003102:Colloids; D004058:Diffusion; D004285:Dogs; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008962:Models, Theoretical; D010974:Platelet Aggregation; D011817:Rabbits
D003102:Colloids; D000001:Calcimycin; D000244:Adenosine Diphosphate