Intracellular reduced glutathione concentrations of in vivo–aged biotinylated dog RBCs. Positive (▾) biotinylated and negative (○) RBCs were isolated from dog no. 1630 at the indicated times post-biotinylation by magnetic cell sorting. In addition, a presort (•) RBC sample was collected from dog no. 1630 before each separation by magnetic cell sorting. Samples were assayed in triplicate for intracellular reduced glutathione and the mean (±SD) is shown.