Transendothelial transport (transcytosis) of iron‐transferrin complex in the rat liver

Abstract

To determine the transport pathway of iron-transferrin complex (Fe-TF) into the hepatocyte, we labeled Fe-TF with colloidal gold and perfused rat liver through the portal vein with this probe under different conditions. The tissue was then studied by transmission electron microscopy. At a cold temperature (approximately 4 degrees C), the probe bound to the luminal surface of sinusoidal endothelium without internalization. The binding was limited to the endothelium and there was no binding to Kupffer cells or hepatocytes. The binding was inhibitable in the presence of excess soluble Fe-TF, indicating the specificity of the bindings. At 37 degrees C the probe was internalized via a system of coated pits and vesicles. Morphometric analyses of the temporal sequence of events suggested that the probe was transported, in part, across the endothelium via a system of tubules and vesicles and externalized on the abluminal side via a system of coated pits. The probe was then taken up by hepatocytes. Only minimal uptake was noted when gold-labeled bovine serum albumin was used either at the low temperature or at 37 degrees C. The findings suggest that the liver uptake of Fe-TF complex by hepatocytes is a transendothelial phenomenon (transcytosis).

Receptor‐mediated transcytosis of follicle‐stimulating hormone through the rat testicular microvasculature

“…This is the case of ceruloplasmin (Kataoka and Tavassoli, 1985), transferrin (Kishimoto and Tavassoli, 1987), and glucagon (Watanabe et al, 1988) in the microvessels of hepatic sinusoids. The presence of trancytotic receptors for these plasma components in endothelial cells of hepatic sinusoids is surprising because these cells contain large gaps (up to one hundred nanometers in diameter) and thus the molecules should have free access to the hepatocytes.…”

Endothelial Transcytosis of Iron-Transferrin in the Liver Does Not Involve Endosomal Traffic

“…We have previously shown that liver endothelium me diates the uptake of Fe-Tf by hepatocytes [13][14][15][16]. Using in situ perfusion of colloidal gold-labeled Fe-Tf combined with electron microscopy, we have shown that the endo thelium takes up Fe-Tf on the luminal side via a receptormediated mechanism.…”

Desialation of transferrin by rat liver endothelium.

“…Cells were suspended in Dulbecco PBS (D-PBS) to a final concentration of4 X 106 cells/ml. They were partially fractionated into large (hepatocytes) and small cell fractions using metrizamide doublelayer centrifugation as described (8,9,(21)(22)(23)(24)(25). To further purify endothelial cells, centrifugal elutriation was used (8,12).…”

“…Crude liver cell suspensions were obtained from Sprague-Dawley rats, which weighed 150-250 g, using the collagenase perfusion method (8,9,(21)(22)(23)(24)(25). Cells were suspended in Dulbecco PBS (D-PBS) to a final concentration of4 X 106 cells/ml.…”