Summary Glycogenolysis, glycogenesis, glyconeogenesis and the enzymes phosphorylase, glycogen synthetase, and fructose‐1–6‐diphosphatase were investigated in heavy and light platelet populations in order to determine the presence or extent of metabolic heterogeneity. The mean volume of the heavy platelets was approximately 2.4‐fold greater than that of the light platelets. Heavy platelets contained 3.4‐fold more glycogen and had a 5.9‐fold greater rate of glycogenolysis per g wet weight, than light platelets. Heavy platelets incorporated 5.9‐fold more [14C]glucose into platelet glycogen when data were expressed per g wet weight, and 1.7‐fold more [14C]glucose when data were expressed per μmole of glycogen. This difference in glycogen synthesis was paralleled by a 1.8‐fold greater glycogen synthetase activity. Heavy platelets incorporated 3.0‐fold more [14C]citrate into platelet glycogen when data were expressed per g wet weight, and 1.4‐fold more [14C]citrate when data were expressed per μmol of glycogen. Similar results were obtained utilizing [14C]pyruvate as precursor. This difference in glyconeogenesis was paralleled by a 2.5‐fold greater fructose‐1–6‐diphosphatase activity for heavy platelets.
SummaryAn albumin density gradient was employed to separate rabbit platelets into heavy and light populations. Compared to a previous inert oil density gradient, the albumin gradient had the advantage of greater resolution, easier suspension of isolated platelet populations, and more physiologic composition. Heavy platelets were found to be enriched with large platelets, containing 2.3 fold more platelets with 2 μ diameter and 2 fold less platelets with 1 μ diameter. Platelets of 3 and 4 μ diameters were found in the heavy population but not in the light population. In vivo labelling of megakaryocytes with Se75-selenomethionine revealed early preferential labelling of heavy platelets when compared to light platelets, with an average heavy/light ratio labelling index of 3.7 on days 1–2, declining to 1.4 on days 3–4 and 0.7 on day 6. These data support previous data that heavy-large platelets are young platelets.
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