Endocytosis of formaldehyde-denatured serum albumin by nonparenchymal liver cells in vitro.

The uptake and degradation of 125I-labeled formaldehyde-denatured serum albumin in nonparenchymal rat liver cells were studied in vitro. Nonparenchymal cells bound formaldehyde-denatured serum albumin at two types of binding site, one with a high affinity and one a low affinity. The number of high affinity binding sites was approx. 10(5) per cell and the association constant, Ka 10(8) M-1. Inhibition of protein synthesis with cycloheximide did not affect the uptake and degradation of formaldehyde-denatured serum albumin suggesting reutilization of the binding sites. The presence of monensin-reduced uptake and degradation to less than 10% of control values. Pronase treatment of nonparenchymal liver cells completely abolished the uptake and degradation of the ligand. The uptake mechanism was not specific for formaldehyde-denatured serum albumin. Unlabeled acetylated, as well as malondialdehyde treated, serum albumin reduced the uptake of 125I-labeled formaldehyde-denatured serum albumin as effectively as unlabeled formaldehyde-denatured serum albumin itself.