title: Evidence that platelet density depends on the alpha-granule content in platelets.
abstract: The relation between platelet buoyant density and beta-thromboglobulin (beta-TG), a marker for platelet alpha-granule content, was assessed by three independent approaches. (1) Platelets were separated on iso-osmolar discontinuous Stractan density gradients into five fractions, ranging in density from 1.061 g/ml to 1.091 g/ml (20 degrees C). The beta-TG content (mean +/- SD, n = 17) increased with the platelet density from 27.8 +/- 8.6 micrograms beta-TG/10(9) cells (20% less-dense platelets) up to 65.6 +/- 15.5 micrograms beta-TG/10(9) cells (15% most-dense platelets). (2) Activation of platelets in platelet-rich plasma with thrombin, adenosine diphosphate, collagen, or epinephrine resulted in a decreased density of the platelets. This was only seen when there was simultaneous secretion of beta-TG. (3) The less-dense and the more-dense platelet fractions, after isolation by density gradient centrifugation, were separately treated with thrombin. After complete degranulation, the density distribution of the originally less-dense and more-dense platelets were identical and were much narrower than the density distribution of resting platelets.
mesh_terms: D000328:Adult; D001609:Beta-Globulins / Q000032:analysis*; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure*; D002499:Centrifugation, Density Gradient; D003594:Cytoplasmic Granules / Q000032:analysis*; D003720:Densitometry; D006801:Humans; D013917:Thrombin / Q000494:pharmacology; D001620:beta-Thromboglobulin / Q000032:analysis* / Q000378:metabolism
chemical_list: D001609:Beta-Globulins; D001620:beta-Thromboglobulin; D013917:Thrombin