title: Collagen-induced exposure of anionic phospholipid in platelets and platelet-derived microparticles.
abstract: We have shown recently that the calcium-dependent phospholipid-binding protein annexin V (placental anticoagulant protein I) can be used to study the exposure of anionic phospholipid after platelet activation. In this study we have further examined the mechanism of this process. Collagen-induced exposure of annexin V binding sites correlated directly with increased ability to support activity of the reconstituted prothrombinase complex. The potency of annexin V as an inhibitor of platelet prothrombinase was the same as its Kd for platelets. Prior incubation of platelets with 5'-p-fluorosulfonylbenzoyladenosine or p-chloromercuribenzenesulfonate had no significant effect on annexin V binding. Similarly, inhibition of platelet cyclic endoperoxide synthesis by acetylsalicylic acid or indomethacin did not inhibit annexin V binding. Staurosporine inhibited collagen-induced, but not A23187-induced, annexin V binding. Agents that increase intraplatelet cyclic nucleotides partially inhibited collagen-induced annexin V binding. Thus, collagen-induced exposure of anionic phospholipid appears to depend primarily on increases in intraplatelet free calcium and may be independent of ADP- or endoperoxide-mediated pathways. Binding sites for annexin V on microparticles derived from collagen-stimulated platelets were demonstrated by flow cytometry and gel filtration. In addition, prior incubation of platelets with 100 nM annexin V inhibited factor Va binding to both platelets and platelet-derived microparticles. These results support the concept that the procoagulant effect of platelets and platelet-derived microparticles is mediated by calcium-induced exposure of anionic phospholipids.
authors.affiliation: Department of Medicine, University of Washington, Seattle 98195.
authors.forename: P
authors.initials: P
authors.lastname: Thiagarajan
authors.forename: J F
authors.initials: JF
authors.lastname: Tait
mesh_terms: D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000345:Affinity Labels; D000470:Alkaloids / Q000494:pharmacology; D000838:Anions; D017304:Annexin A5; D001665:Binding Sites; D001792:Blood Platelets / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002135:Calcium-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D003094:Collagen / Q000494:pharmacology*; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D015943:Factor Va / Q000037:antagonists & inhibitors; D005434:Flow Cytometry; D006801:Humans; D009599:Nitroprusside / Q000494:pharmacology; D010743:Phospholipids / Q000378:metabolism*; D010974:Platelet Aggregation; D011257:Pregnancy Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000494:pharmacology; D015398:Signal Transduction; D019311:Staurosporine; D013806:Theophylline / Q000494:pharmacology; D013925:Thromboplastin / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D000345:Affinity Labels; D000470:Alkaloids; D000838:Anions; D017304:Annexin A5; D002135:Calcium-Binding Proteins; D010743:Phospholipids; D011257:Pregnancy Proteins; D009599:Nitroprusside; D005576:Colforsin; C016276:8-bromocyclic GMP; D000001:Calcimycin; D002731:4-Chloromercuribenzenesulfonate; D003994:Bucladesine; D015943:Factor Va; C010959:5'-(4-fluorosulfonylbenzoyl)adenosine; D003094:Collagen; D013925:Thromboplastin; D013806:Theophylline; D006152:Cyclic GMP; D019311:Staurosporine; D000241:Adenosine