FUNCTIONAL FRACTIONATION OF PLATELETS

  • 1 January 1981
    • journal article
    • research article
    • Vol. 97  (2) , 187-204
Abstract
Studies of [human] platelet populations suggest that they are heterogeneous in size, age and metabolic parameters. To correlate these parameters with efficiency of aggregation, a new technique, functional fractionation, was developed. Platelet populations are separated by their differentiation rectivity to aggregating agents. Low doses of ADP (0.1 to 0.7 .mu.M) are added to stirred PRP [platelet-rich plasma], after which gentle centrifugation is used to remove aggregates from single unreacted platelets. The loose aggregates can be readily dispersed for comparison of the physical or biochemical properties of the reacted vs. unreacted platelets. Reactive platelets were larger (6.5 .mu.m3) than unreacted platelets (5.51 .mu.m3). No significant difference in density existed between the 2 populations; no release of [14C]serotonin from prelabeled platelets occurred during functional fractionation. Scanning and transmission EM confirmed the size difference and revealed that in both populations platelets were structurally intact with a normal discoid shape and no significant difference in organelle content. Human platelets most reactive to ADP were also enriched in glycogen (3.6-fold), ATP (1.6-fold) and ADP (2-fold), compared with less reactive cells. These reactive cells took up more 51[Cr] and contained 1.9 times more surface sialic acid. In an in vivo aging experiment, rats were injected with 75[Se]methionine. Shortly after labeling (1 day), the most reactive platelets possessed the highest amount of 75[Se]. Functionally active platelets, which are also larger, apparently are more active metabolically than less reactive platelets, possess a higher negative surface charge and may be a younger population.