Journal
BRITISH JOURNAL OF HAEMATOLOGY
Volume 144, Issue 4, Pages 591-602Publisher
WILEY
DOI: 10.1111/j.1365-2141.2008.07506.x
Keywords
platelet; microparticles; apoptosis; calpain; alpha IIb beta 3 integrin
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Funding
- Deutsche Forschungsgemeinschaft [SFB688]
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Platelets stimulated by a combination of thrombin/convulxin have been shown to develop two to three populations characterized by different phosphatidylserine (PS) surface expression and integrin alpha IIb beta 3 activity. To determine how these markers are distributed on the surface of platelets/particles, we studied Annexin V and PAC-1 binding to platelets/particles of different sizes by flow cytometry analysis and evaluated influences of calpain and caspase inhibitors on thrombin/convulxin-activated platelets. Analysed platelets/particles were divided by their sizes, according to the standard size beads, into seven populations from 0.37 to 4.8 mu m. PAC-1 binding/mu m(2) was almost equal in platelets/particles ranging from 1.2 to 4.8 mu m and was significantly lower on smaller-sized particles sizes (0.37-0.7 mu m). PS surface exposure/mu m(2) was high in the particles of 0.37-1.2 mu m and very low in platelets (2.6-4.8 mu m). Upon thrombin/convulxin stimulation caspase inhibitors prevented microparticle (MP) formation, while a calpain inhibitor stimulated MP formation. It was also shown that stimulated platelets are heterogeneous not only in their ability to activate alpha IIb beta 3 integrin complex and expose PS on their surface, but also in the distribution of activation markers, which strongly depends on platelet/particle size and that platelets/particles of different sizes provide different responses to the same stimulus.
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