Inhibition of reticulocyte iron uptake by NH4Cl and CH3NH2

The aim of this investigation was to test the hypothesis that elevation of intracellular pH would inhibit iron uptake by reticulocytes. The experiments were performed with rabbit reticulocytes and iron bound to rabbit transferrin. Incubation of the cells with NH4Cl, (NH4)2CO3, CH3NH2 and (CH3)2NH was used in an attempt to increase intracellular pH. These substances were all found to inhibit iron uptake by reticulocytes. The mechanism of action of NH4Cl and CH3NH2 was investigated in detail. Similar results were found with both reagents. They inhibited iron uptake in a concentration-dependent manner, but produced a small increase in the cellular uptake of transferrin. The onset of action was rapid and the effect was reversible. There was no decrease in the number of transferrin-binding sites per cell and their apparent affinity for transferrin increased slightly, while the efficiency of iron removal from transferrin per binding site diminished greatly. The rate of transferrin release from reticulocytes was unaffected. NH4Cl did not affect the rate of iron release from transferrin in a cell-free system. Incubation of reticulocytes with 10 mM NH4Cl or CH3NH2 was found to produce an increase in intracellular pH of 0.05-0.15 pH units. The intracellular pH determined by use of the weak acid 5,5-dimethyloxazolidine-2,4-dione was significantly higher than that obtained with the weak base (CH3)2NH. By transmission electron microscopy it was shown that reticulocytes treated with NH4Cl or CH3NH2 have enlarged intracellular vesicles. The results are considered to support the hypothesis that iron release from transferrin in reticulocytes occurs as a result of protonation of the transferrin within intracellular vesicles. According to this hypothesis, weak bases such as NH3 and CH3NH2 inhibit iron release by neutralizing H+ within the vesicles.