Uptake and subcellular distribution of injected transferrin in rat liver.

Radioactively labelled transferrin was injected into rats intravenously and its uptake and subcellular distribution in the liver was investigated. The amount of radioactivity in the liver remained constant from 10 min after injection. It was not influenced by asialoglycoproteins. The radioactive label was identified as asialotransferrin. After subcellular fractionation by differential and zonal sucrose density-gradient centrifugation the label was enriched in a low-density endocytic compartment showing fluorescence quenching of acridine orange and N-ethylmaleimide-sensitive ATPase activity. The data fit into a model of continuous transferrin-receptor-mediated recycling through the hepatocyte's endocytic compartment.