Uptake of iron by isolated rat hepatocytes from a hydrophilic impermeant ferric chelate, Fe(III)-DTPA.

We studied uptake of iron from Fe(III)-diethylenetriamine pentaacetate (DTPA) in isolated rat hepatocytes. This uptake is specific with an affinity of 600 nM and shows an optimum pH of 6. The specificity is indicated by inhibition by ferric citrate and diferric transferrin. Iron uptake from Fe(III)-DTPA is completely inhibited by trypsinization of the cell surface, by strong impermeant ferric chelators (DTPA, apo-transferrin, polymer-conjugated desferrioxamine), both hexacyanoferrates, copper and zinc, and partly by dipyridyl, manganese, cobalt, N-ethylmaleimide, and citrate. The lysosomotropic agent chloroquin inhibits weakly; proton pump inhibitors are without effect. Ascorbate and Tiron both effectively stimulate the uptake and also mobilize iron from DTPA in vitro. Approximately 75% of the freshly acquired intracellular iron is found in ferritin even after uptake at lowered temperature (16 degrees C). We conclude that a rate-limiting mobilization of iron from the DTPA chelate by a cell-surface activity is required before iron can actually enter the cell. This can be enhanced by mediators of iron release, but does not seem to require reduction of iron. The use of DTPA as chelator offers the possibility of studying this putative activity because the Fe(III)-DTPA chelate is stable in the presence of transferrin or desferroxamine, in contrast to ferric citrate or Fe(NTA)2.