Erythropoietin effects on iron metabolism in rat bone marrow cells.

This paper describes a study of the incorporation of 59-Fe from 59-Fe-labelled rat transferrin into rat bone marrow cells in culture. 59-Fe was found in both stroma and cytoplasm of marrow cells, and the cytoplasmic 59-Fe separated by polyacrylamide gel electrophoresis, into ferritin, haemoglobin and a low molecular weight fraction. The incorporation of 59-Fe into all three cytoplasmic fractions, but not into the stroma, increased progressively with time. Erythropoietin stimulated the increase of 59-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 59-Fe incorporated into the stroma and low molecular weight iron fractions during a 1 h incubation with 59-Fe-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 59-Fe fluxes. The erythropoietin stimulation of 59-Fe incorporation into ferritin, one of the earliest erythropoietin effects to be recorded, was therefore considered to be due to an increase of 59-Fe uptake by the hormone-responsive cells rather than a direct effect on ferritin synthesis. 20-h cultures containing erythropoietin when incubated with 59-Fe-labelled transferrin for 4 h, showed dose-related erythropoietin stimulation of 59-Fe incorporation into haemoglobin only. In the presence of 10 mM isonicotinic acid hydrazide, 59-Fe incorporation into haemoglobin was inhibited, as in reticulocytes (Ponka, P. and Neuwrit, 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.