Erythropoietin effects on iron metabolism in rat bone marrow cells

This paper describes a study of the incorporation of ^{5 9}Fe from ^{5 9}Fe-labelled rat transferrin into rat bone marrow cells in culture. ^{5 9}Fe was found in both stroma and cytoplasm of marrow cells, and the cytoplasmic ^{5 9}Fe separated by polyacrylamide gel electrophoresis, into ferritin, haemoglobin and a low molecular weight fraction.The incorporation of ^{5 9}Fe into all three cytoplasmic fractions, but not into the stroma, increased progressively with time. Erythropoietin stimulated the increase of ^{5 9}Fe in ferritin within 1 h, the earliest time examined, and more than 3 h later in the stroma and haemoglobin.A proportion of the ⁵⁹Fe incorporated into the stroma and low molecular weight iron fractions during a 1 h incubation with ⁵⁹Fe-labelled transferrin was mobilised into ferritin and haemoglobin during a subsequent 4-h “cold-chase”. Erythropoietin, when present during the “cold-chase”, did not influence these ⁵⁹Fe fluxes. The erythropoietin stimulation of ⁵⁹Fe incorporation into ferritin, one of the earliest erythropoietin effects to be recorded, was therefore considered to be due to an increase of ⁵⁹Fe uptake by the hormone-responsive cells rather than a direct effect on ferritin synthesis.20-h cultures containing erythropoietin when incubated with ⁵⁹Fe-labelled transferrin for 4 h, showed dose-related erythropoietin stimulation of ⁵⁹Fe incorporation into haemoglobin only.In the presence of 10 mM isonicotinic acid hydrazide, ⁵⁹Fe incorporation into haemoglobin was inhibited, as in reticulocytes (Ponka, P. and Neuwirt, J. (1969) Blood 33, 690–707), while that into the stroma, ferritin and low molecular weight iron fractions, was stimulated; there were no reproducible effects of erythropoietin.