Collagen and thrombin induced platelet activation were examined, in vitro, with regard to the appearance of surface-associated Factor V-like activity (PF1) and catalytic phospholipid-like surface activity (PF3). Two test systems were used: a clotting assay (a modified KAPTT) and a chromogenic substrate assay (maximum hydrolysis of S-2238). Following stimulation of normal platelets, both PF1 and PF3 appeared simultaneously in the supernatant and platelet pellet. When normal platelets were collected and carefully washed in a buffer containing adenosine, PGE1, and theophylline, the appearance of both PF1 and PF3 was blocked, as was the release of ATP from dense granules, the release of β-TG and PF4 from α-granules, and the occurrence of aggregation. When platelets were collected in this same inhibitor-containing buffer, and then gel filtered/centrifuge-washed in an inhibitor-free buffer, the appearance of PF1 and PF3 was still blocked. This occurred even though release of ATP, β-TG and PF4 as well as aggregation followed a pattern equivalent to platelets never exposed to these inhibitors. When the release supernatant from normal platelets isolated in the absence of inhibitors was gel filtered on Sepharose CL-4B in the presence of EDTA, the carbohydrate-free, lipid- protein particles (70-170nm diam.) that provide PF3 appeared in the void volume. When the release supernatant from normal platelets was gel filtered in the presence of Ca2+, both, PF1 and PF3 eluted in the void volume. With platelets isolated from severe F.V-deficient donors, only PF3 was found in the void volume, in the presence or absence of Ca2+. It seems that the appearance of PF1 and PF3 as coagulant activities is completely separate from both the release of dense granule and α-granule contents as well as platelet aggregation and that the appearance of PF1 requires the presence of Ca2+.
Fluctuating Diffusivity of RNA-Protein Particles: Analogy with Thermodynamics
