Transferrin receptor on rat Kupffer cells in primary culture

Kupffer cells may play a role in the turnover of iron in acute viral hepatitis. The transferrin receptor of rat Kupffer cells in primary culture was therefore investigated in this study. Daily specific bindings on 125I-diferric transferrin (Tf) to rat Kupffer cells in primary culture from day 3 to day 6 of culture were 1.64 +/- 0.08%, 4.16 +/- 0.05%, 4.34 +/- 0.07% and 2.63 +/- 0.07%, respectively. The specificity of the Tf binding sites was examined by competition studies showing that galactose (30 mmol x l-1) and ovalbumin (90 mumol x l-1) did not compete for the binding sites, but human lactoferrin (50 mumol x l-1) competed for the binding sites by about 30%. The affinity and capacity of Tf receptor on rat Kupffer cells in 5-day culture were analyzed according to the method of Scatchard. A single class of 125I-diferric Tf binding sites with an affinity constant of 1.65 x 10(7) l x l-1) and a capacity of 6.86 x 10(6) sites/cell was found. After zymosan (500 micrograms/ml) preincubation for 30 min, the binding capacity increased about 1.7-fold, and this increase depended upon the increase of the affinity of Tf receptor. These data suggest that Kupffer cells in the activated state accelerate the removal of elevated serum iron.