Factors affecting transport changes associated with reticulocyte maturation

Maturation and aging of the mammalian red blood cell is characterized by the loss in many cytoplasmic and membrane functions including ion and solute transport. We have used long-term in vitro incubation of sheep reticulocytes to examine the nature of several membrane transport changes. Three distinct transport systems have been studied, namely the Na,K-pump measured as specific [3H]ouabain binding sites, Na+/glycine cotransport and the nucleoside transporter measured as specific [3H]nitrobenzylthioinosine binding. As reported previously for the Na,K-pump and Na+/glycine cotransport (Weigensberg, A.M. and Blostein, R., Proc. Nat. Acad. Sci. 80:4978-4982, 1983), the losses of all three functions are diminished markedly by energy (ATP) depletion. Furthermore, for at least one of the transport systems, the Na,K-pump, the maturation-associated loss is modulated by ligand-induced perturbations which are known to effect specific protein conformational changes.