PLATELET MICROPARTICLES - A CARRIER OF PLATELET-ACTIVATING-FACTOR

Platelet-activating factor (PAF) has been considered to be released in a soluble form from activated platelets. Also a considerable number o f microparticles were released from stimulated platelets. To evaluate the possibility that microparticles contain PAF, the amount of PAF in whole activated platelets, microparticles and tile suspending medium w as determined by means of bioassay. The total amount of PAF released f rom 3 x 10(8) platelets activated with thrombin (0.5 U/ml) plus collag en (10 mu g/ml) for 10 minutes was 4.6 +/- 1.5 x 10(-12) mol (n = 8, m ean +/- S.D.). Eighty-seven percent of the PAF released from platelets was associated with microparticles. PAF released in microparticles is susceptible to plasma acetylhydrolase and may be localized on the out er surface of microparticles. This is the first report implicating the role of microparticles as a novel carrier of mediators formed in the cells. (C) 1996 Academic Press, Inc.