DIFFERENTIAL EXPRESSION OF PLATELET ACTIVATION MARKERS CD62P AND CD63FOLLOWING STIMULATION WITH PAF, ARACHIDONIC-ACID AND COLLAGEN

The effects of varying concentrations of platelet-activating factor (P AF), arachidonic acid (AA) and collagen on the expression of the plate let activation markers CD63 and CD62P were assessed in 10 normal subje cts using flow cytometry. CD63 expression was significantly greater th an CD62P expression, with PAF (80 nM) inducing mean maximum CD63 expre ssion of 32.9 +/- 6.4% and mean maximum CD62P expression of 5.5 +/- 1. 8%. AA (1 mM) induced maximum CD63 expression of 37.7 +/- 7% and maxim um CD62P expression of 9.3 +/- 1%, Collagen (2-80 mu g/ml) induced min imal expression but 800 mu g/ml induced mean CD63 expression of 33.1 /- 4.1% and mean CD62P expression of 6.1 +/- 0.8%. Greater CD63 and CD 62P expression were induced by phorbol myristate acetate (1.6 mu M, 70 .9 +/- 11% and 69.4 +/- 9.9%, respectively) and thrombin (0.1 U/ml, 70 .7 +/- 9.3% and 73.5 +/- 5.4%, respectively). With PAF and collagen on ly one platelet population was detected whereas with 1 mM AA two popul ations were observed. These results indicate that expression of platel et adhesion receptors depends on the nature and concentration of agoni st and that subpopulations of platelets may exist. Importantly, PAF co ncentrations inducing moderate CD63 and CD62P expression did not induc e platelet aggregation, suggesting that platelets can be activated ind ependently of aggregation.