Heterogeneity of hypotonically loaded rat erythrocyte populations as detected by counter-current distribution in aqueous polymer two-phase systems.

Carrier rat erythrocytes loaded with exogenous substances ([125I] carbonic anhydrase) by hypotonic-isotonic dialysis become heterogeneous cell populations that can be fractionated using the counter-current distribution (CCD) technique. Two well-defined low- and high-partition ratio, G, subpopulations are obtained in charge-sensitive dextran-polyethylene glycol two-phase systems. The low-G subpopulation, which contains the most fragile and surface-altered cells, as deduced from their osmotic fragility curves and partition behaviour, respectively, presents a high amount of exogenous substance incorporated (134.6 cpm/10(6) cells). The high-G subpopulation, that contains cells similar to the control or isotonically dialyzed cells presents a lower amount of exogenous substance incorporated (69.8 cpm/10(6) cells). Cells in this high-G subpopulation seem to be fractionated, like the controls, according to ageing as suggested by the decline of the pyruvate kinase specific activity from the left- to the right-hand side of the CCD profile.