Partition of cells in two-polymer aqueous phases can be used to detect and trace differences and changes in certain membrane surface properties as a function of in vivo maturation and aging and in vitro treatments. The countercurrent distribution of rat erythrocytes and bone marrow cells which have been X-irradiated (1000 rads) give patterns identical to those previously found with the corresponding normal cells. Membrane changes associated with reticulocyte maturation are observed to proceed normally in irradiated rats (1000 rads). However,59 Fe injection into a rat 30 hr after X-irradiation followed (18 hr later) by countercurrent distribution of peripheral red cells reveals that the youngest reticulocytes are absent from the blood. The label is present only in the oldest reticulocytes and youngest erythrocytes. Cells derived from the bone marrow of in vivo irradiated rats (6 or more hr after irradiation, 1000 rads) contain a large quantity of erythrocytes which have the same surface properties (i.e., partition) as peripheral erythrocytes. Our studies indicate that irradiation at the level used has no effect, measurable by this most sensitive means (i.e., partition), on the membrane surface properties of formed cells. Most readily apparent is the marked effect on cell biosynthesis itself.

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