Differences in Schedules of Regression of Transport Systems during Reticulocyte Maturation

Based on a description of the difference in the transport characteristics for amino acids of a reticulocyte-rich population of young blood cells and the mature erythrocyte, the schedule of these changes during maturation has been studied during an interval of 17 days after administering phenylhydrazine to rabbits. All amino acid transport activities studied tended to reach their maxima several days after the peak in the reticulocyte count, and during an interval when the reticulocyte morphology was being lost rapidly. Subsequently, different schedules were followed for the regression of otherwise discernible transport activities. The activity for alanine was lost most rapidly; a Na+-dependent component of the uptake of α,γ-diaminobutyric acid, which was, however, not inhibitable by alanine or glycine, appeared to be lost about as rapidly. A Na+-independent transport of lysine, which applied also to other cationic amino acids, regressed much more slowly, and was to a considerable degree retained at maturity. The uptake of glycine was also lost slowly, a kinetic complexity persisting throughout. The complexity may mean that two glycine transport systems are present. Support for this view was not obtained either by the test of analogues for differential inhibition of the two components or by the finding of any difference in the rate of regression during reticulocyte maturation.