Heterogeneity of Rabbit Platelets. I. Employment of an Albumin Density Gradient for Separation of a Young Platelet Population Identified with Se75-Selenomethionine

Abstract

An 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.