The influence of gallium and other metal ions on the uptake of non-transferrin-bound iron by rat hepatocytes.
BACKGROUND
Under conditions of iron overload non-transferrin-bound iron (NTBI) occurs in the circulation and is mainly cleared by the liver. Beside iron, gallium and aluminum enhance accumulation of NTBI. We try to characterize the mechanism and metal-mediated regulation of NTBI uptake using cultivated primary rat hepatocytes.


METHODS
Hepatocytes from rat liver were incubated with 0.1 mg/ml transferrin (as control), with ferric ammonium citrate or other di- and trivalent metal salts and the uptake of (55)Fe-labeled Fe-diethylene triammine pentaacetate was measured.


RESULTS
Uptake rates for iron increased from 0.3 to 2.1 pmol/mg protein per min in cells preincubated for 5 hours with 300 microM ferric ammonium citrate, to 1.7 pmol/mg protein per min with gallium and to 1.2 pmol/mg protein per min with aluminum. Maximal stimulation was obtained with 300 microM iron and 600 microM gallium. Preincubation with divalent metals was ineffective. NTBI uptake was specific for iron, partly inhibited by gallium citrate, diferric transferrin and completely inhibited by apotransferrin in control and gallium-treated cells. In iron-loaded cells, inhibition of NTBI uptake by diferric transferrin completely disappeared within 2 hours.


CONCLUSIONS
These experiments show that hepatocytes do respond to the presence of trivalent metals by an increased transport capacity to sequester these ions. The metals seem to have at least partly different mechanisms of transport stimulation.
Sturm
B
B
Department of Medical Chemistry, Medical University of Vienna, Waehringerstr. 10, 1090 Vienna, Austria.
Lassacher
U
U
Ternes
N
N
Jallitsch
A
A
Goldenberg
H
H
Scheiber-Mojdehkar
B
B
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002412:Cations / Q000737:chemistry; D002951:Citrates / Q000494:pharmacology*; D005290:Ferric Compounds / Q000494:pharmacology; D005708:Gallium / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D007501:Iron / Q000378:metabolism*; D008099:Liver / Q000166:cytology / Q000187:drug effects; D008297:Male; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013379:Substrate Specificity
D002412:Cations; D002951:Citrates; D005290:Ferric Compounds; D000644:Quaternary Ammonium Compounds; D005708:Gallium; D007501:Iron; C103850:gallium citrate; C013531:ferric ammonium citrate