Fractionation of platelets according to size: Functional and biochemical characteristics

Abstract

The functional and biochemical heterogeneity of platelets has been studied using graded differential centrifugation to fractionate human platelets according to size while maintaining their morphological and functional integrity as indicated by scanning electron microscopy and content of beta-thromboglobulin. Aggregation kinetics were studied by both optical and quenched-flow methods involving single-particle counting. Large platelets were significantly more sensitive to ADP, but aggregated less rapidly than small platelets. Thrombin exerted a similar influence. Large platelets were also enriched in surface sialic acid and sulfhydryl groups and in internal glycogen, ATP, ADP, calcium, cyclic AMP, malonaldehyde, and succinate cytochrome c reductase when compared to small platelets, even when normalized per unit volume. ADP caused a more rapid breakdown of cyclic AMP in small platelets. Potential aging relationships were tested by isotope studies in rats. 75Se-selenomethionine was incorporated in vivo at a similar rate into all fractions. Large platelets labeled with 51Cr disappeared from circulation linearly and had a longer mean lifespan than small platelets, which disappeared exponentially. This behavior supports independent aging of platelet populations of differing size. The data suggest a distinct heterogeneity in platelet function and fate, which could derive from protection of large platelets against excessive activation by Ca2+-regulated events.

Mepacrine-Labeled Platelet Dense-Body Number in Patients with Chronic Uremia

“…Leithner et al [5] have observed the aggregates on dialyzer membrane, whereas Guzzo et al [3] have found increase levels p-thromboglobulin, in hemodialysed patients, a marker of platelet activation and destruction in vivo. Because greater plate lets with higher numbers of dense granules are more sensitive to activation than smaller ones [1] our results may suggest that this type of platelets is likely eliminated first from the circulation after contact w'ith dialyzer mem branes.…”

Platelet calcium and quenched-flow aggregation kinetics in essential hypertension.

“…These small cells contain the lowest specific content of glycogen, an observation consistent with increased resting levels of cytosolic calcium and a more active phosphorylase kinase. 33 In essential hypertension there may be a shift in the nature of the platelet population, perhaps as a result of an alteration at the precursor level, or an abnormal conditioning during circulation. We might have predicted an alteration in platelet size, 3033 but we found no difference (Table 4) between hypertensive and normotensive groups.…”

“…45 The question of heterogeneity of platelet size and function has interested investigators for some time. Although there are clear differences in function and biochemical characteristics, 33 it is generally agreed that platelet size does not correlate with platelet age. 33 -4647 A number of mechanisms, confirmed and presumptive, responsible for elevated platelet [Ca 2+ ]; in hypertension have been proposed.…”

“…Conversely, Catalano et al, 52 in a study of patients with severe hypertension and associated peripheral vascular disease, reported no difference in plasma /3-thromboglobulin concentrations within the range of normal values. Other investigators 45 - 33 have con-tended that venous /3-thromboglobulin levels in patients with World Health Organization (WHO) Class I disease do not differ significantly from those in age-and sex-matched controls, but these levels are significantly increased in the more advanced stages of hypertension (WHO Classes II-IU). 53 However, even this finding was not confirmed by others.…”

Different adhesion types and active sensitivity of platelet subpopulations

“…It is generally accepted that platelets adhere to the vessel wall, as they are stimulated by being exposed to injured endothelium [ 11. There are studies indicating that only a small part of blood platelets is actively involved in the platelet-vessel wall interaction [ 2 , 3 ] . With respect to heterogeneous morphological and functional characteristics, the existence of different subpopulations of platelets was proposed [4][5][6][7]. However, little is known as to whether the adhesion features of platelets and the related biochemical properties are different in such subpopulations.…”