Partition of cells in dextran-polyethylene glycol aqueous phases is an extremely sensitive method for separating cells and for tracing subtle changes in the cells’membrane surface as a function of differentiation, maturation and ageing. By appropriate manipulation of polymer concentration and ionic composition and concentration one can select, to a great extent, the membrane properties (e.g. charge-associated, lipid-related) that will determine the cells’partition coefficient. Combining radioiosotopic labelling and cell countercurrent distribution techniques we have previously reported rapid increases in charge-associated partition coefficients during rat reticulocyte maturation followed by slower decreases in the partition coefficients during the entire life span of the mature erythrocyte. In the present experiments red blood cell populations containing radioisotopically labelled cells of different and distinct ages have been subjected to countercurrent distribution in phase systems reflecting either membrane charge-associated or lipid-related characteristics. It was found that: (a) membrane lipid-related surface properties change rapidly during reticulocyte maturation; (b) membrane charge-associated changes during reticulocyte maturation are discerned prior to those that are lipid-related; and (c) lipid-related membrane changes continue slowly throughout the entire life-span of the erythrocyte.

The sensitivity with which red cell membrane lipid-related differences or changes can be detected and measured by cell partition suggests great usefulness of this simple method in the study of abnormalities in red cell lipids.