monensin and ethylamine

Through a process resembling receptor-mediated internalization, liver endothelium binds and internalizes iron-transferrin (Fe-Tf) complexes, transporting them from the luminal to abluminal side. Since in most systems, the path of receptor-mediated endocytosis leads to the endosomal compartment where the medium is acidified, it is expected that Fe and Tf become dissociated in this acidified medium. However, experiments with double labeling (59Fe, 125I-Tf) indicate that these remain associated. To determine whether the endosomal pathway is used in the course of transendothelial transport of Fe-Tf, experiments were done by incubating purified liver endothelium with radiolabeled Fe-Tf in the presence and absence of endosomal inhibitors, NH4Cl, ethylamine and monensin. The discharge of radiolabeled protein was measured as a function of time. While there was an early phase inhibition in the presence of endosomal inhibitors, the discharge of Tf by endothelium in the presence of inhibitors, reached a plateau comparable to control cells after 4 h, indicating that endosomal inhibition does not inhibit transendothelial transport of Tf and, thus, the transport does not involve endosomal traffic.

Topics: Ammonium Chloride; Animals; Biological Transport, Active; Endocytosis; Endothelium; Ethylamines; In Vitro Techniques; Iron; Liver; Male; Monensin; Rats; Rats, Sprague-Dawley; Transferrin

Through a process resembling receptor-mediated endocytosis, liver endothelium binds and internalizes the plasma glycoprotein ceruloplasmin (CP) on the luminal side. The protein is then transported via a vesicular system to the albuminal side where it is externalized to the space of Disse. In its path, the glycoprotein is fully desialylated. To determine if the endosomal compartment is involved in this transport, we used endosomal inhibitors NH4Cl, ethylamine as well as monensin to quantitatively measure the magnitude of radiolabeled CP transport across purified liver endothelial cells. All three reagents inhibited the transport of CP and its discharge by endothelium. The magnitude of inhibition was dose-related for all three reagents. We conclude that the endosomal compartment is involved in the transendothelial transport of CP across the liver endothelium.

Topics: Ammonium Chloride; Animals; Biological Transport; Ceruloplasmin; Endocytosis; Endosomes; Endothelium; Ethylamines; Hydrogen-Ion Concentration; Liver; Monensin; Rats; Rats, Inbred Strains