scholarly journals Uptake and subcellular processing of 59Fe-125I-labelled transferrin by rat liver

1986 ◽  
Vol 237 (1) ◽  
pp. 163-173 ◽  
Author(s):  
E H Morgan ◽  
G D Smith ◽  
T J Peters
Keyword(s):  
Rat Liver ◽  
Specific Binding ◽  
Bimodal Distribution ◽  
Subcellular Fractionation ◽  
Low Density ◽  
Extracellular Medium ◽  
Density Peak ◽  
Electron Microscope Autoradiography ◽  
Density Fractions

The uptake of transferrin and iron by the rat liver was studied after intravenous injection or perfusion in vitro with diferric rat transferrin labelled with 125I and 59Fe. It was shown by subcellular fractionation on sucrose density gradients that 125I-transferrin was predominantly associated with a low-density membrane fraction, of similar density to the Golgi-membrane marker galactosyltransferase. Electron-microscope autoradiography demonstrated that most of the 125I-transferrin was located in hepatocytes. The 59Fe had a bimodal distribution, with a larger peak at a similar low density to that of labelled transferrin and a smaller peak at higher density coincident with the mitochondrial enzyme succinate dehydrogenase. Approx. 50% of the 59Fe in the low-density peak was precipitated with anti-(rat ferritin) serum. Uptake of transferrin into the low-density fraction was rapid, reaching a maximal level after 5-10 min. When livers were perfused with various concentrations of transferrin the total uptakes of both iron and transferrin and incorporation into their subcellular fractions were curvilinear, increasing with transferrin concentrations up to at least 10 microM. Analysis of the transferrin-uptake data indicated the presence of specific transferrin receptors with an association constant of approx. 5 × 10(6) M-1, with some non-specific binding. Neither rat nor bovine serum albumin was taken up into the low-density fractions of the liver. Chase experiments with the perfused liver showed that most of the 125I-transferrin was rapidly released from the liver, predominantly in an undegraded form, as indicated by precipitation with trichloroacetic acid. Approx. 40% of the 59Fe was also released. It is concluded that the uptake of transferrin-bound iron by the liver of the rat results from endocytosis by hepatocytes of the iron-transferrin complex into low-density vesicles followed by release of iron from the transferrin and recycling of the transferrin to the extracellular medium. The iron is rapidly incorporated into mitochondria and cytosolic ferritin.

On the Role of Transferrin in 67Ga Uptake by Tumor Cells

1988 ◽  
Vol 27 (04) ◽  
pp. 151-153
Author(s):  
P. Thouvenot ◽  
F. Brunotte ◽  
J. Robert ◽  
L. J. Anghileri
Keyword(s):  
Specific Binding ◽  
Subcellular Fractionation ◽  
Animal Blood ◽  
Tumor Bearing ◽  
Cell Structures ◽  
The Difference ◽  
Sarcoma Cells ◽  
In Vitro Uptake

In vitro uptake of 67Ga-citrate and 59Fe-citrate by DS sarcoma cells in the presence of tumor-bearing animal blood plasma showed a dramatic inhibition of both 67Ga and 59Fe uptakes: about ii/io of 67Ga and 1/5o of the 59Fe are taken up by the cells. Subcellular fractionation appears to indicate no specific binding to cell structures, and the difference of binding seems to be related to the transferrin chelation and transmembrane transport differences

Uptake of cholesterol from the very low density lipoprotein or its remnants by the perfused rat liver

1981 ◽  
Vol 59 (6) ◽  
pp. 447-453 ◽  
Author(s):  
Simon-Pierre Noël ◽  
David Rubinstein
Keyword(s):  
Rat Liver ◽  
Lipid Composition ◽  
Low Density Lipoprotein ◽  
Liver Perfusion ◽  
Density Lipoprotein ◽  
Hepatic Uptake ◽  
Low Density ◽  
Perfused Liver ◽  
Very Low Density Lipoproteins

[3H]Cholesterol labelled very low density lipoproteins ([3H]chol-VLDL) were prepared to study the hepatic uptake of cholesterol associated with VLDL and its remnants in the perfused liver system. [3H]Chol-VLDL was incubated with rat postheparin plasma to produce labelled remnants in vitro. The degree of lipolysis of [3H]chol-VLDL depended on the ratio of triacylglycerols to lipase in the incubation medium. Therefore, the produced remnant of d < 1.019 g∙mL−1 had a variable lipid composition depending on the degree of lipolysis. [3H]Chol-VLDL or its remnants were added to liver perfusate and the radioactivity remaining in the perfusate was measured. The kinetic disappearance of [3H]chol-VLDL and its remnants in the perfused liver system indicated that remnant of d < 1.019 g∙mL−1 was taken up by the liver faster than the original VLDL preparation (t1/2 of 8 min vs. 51 min). Appearance of the label in bile during the perfusion was significantly faster when livers were perfused with [3H]chol-VLDL remnants as opposed to uncatabolized [3H]chol-VLDL.The results indicate that first of all, VLDL remnants produced in vitro and reisolated at density less than 1.019 g∙mL−1 do not have a fixed lipid composition but a rather variable one depending on the degree of lipolysis. Secondly, the rat liver may preferentially recognize this VLDL remnant of d < 1.019 g∙mL−1 and take it up more readily than uncatabolized VLDL. Finally when equimolar amount of cholesterol from VLDL or VLDL remnants are circulated in the liver perfusion, the VLDL remnants convey a significantly greater mass of cholesterol to the bile.

scholarly journals Altered hepatic catabolism of low-density lipoprotein subjected to lipid peroxidation in vitro

1994 ◽  
Vol 297 (3) ◽  
pp. 573-579 ◽  
Author(s):  
W L Stone ◽  
M Heimberg ◽  
R L Scott ◽  
I LeClair ◽  
H G Wilcox
Keyword(s):  
Lipid Peroxidation ◽  
Rat Liver ◽  
Low Density Lipoprotein ◽  
Liver Perfusion ◽  
Density Lipoprotein ◽  
Low Density ◽  
Perfusion System ◽  
Oxidatively Modified ◽  
Generating System

Recent evidence suggests that oxidatively modified forms of low-density lipoprotein (LDL) may be particularly atherogenic. In this investigation, the catabolism of human LDL modified by lipid peroxidation in vitro was studied with a recirculating rat liver perfusion system. A dual-labelling technique was used that permitted native LDL and modified LDL to be studied simultaneously in the liver perfusion system. Native human LDL was found to have a fractional catabolic rate (FCR) of 1.00 +/- 0.21%/h, in agreement with other investigators. Subjecting LDL to oxidation for 12 h in the presence of 30 microM FeEDTA did not significantly affect its FCR. LDL treated with a superoxide-generating system (xanthine oxidase, hypoxanthine, O2) in the presence of 30 microM FeEDTA did, however, show a significant increase in FCR (3.23 +/- 0.19%/h). The hepatic uptakes of native LDL and LDL oxidized with FeEDTA+O2 were similar, but both were significantly lower than the hepatic uptake of LDL treated with the superoxide-radical-generating system. The proteolysis of LDL with pancreatin did not influence either its susceptibility to oxidation or its FCR. LDL oxidation resulted in the preferential loss of alpha-tocopherol rather than gamma-tocopherol. These data indicate that the rat liver effectively catabolizes LDL oxidatively modified by treatment with the superoxide-generating system. Furthermore, our results suggest that only very low plasma levels of highly oxidized LDL could be found under conditions in vivo. The liver may therefore play a major role in protecting the arterial vasculature from highly atherogenic forms of LDL.

Acute effects of ethanol on hepatic endocytosis and processing of insulin in perfused rat liver

1993 ◽  
Vol 264 (3) ◽  
pp. E420-E427 ◽  
Author(s):  
J. Fawcett ◽  
B. Hammond ◽  
G. D. Smith
Keyword(s):  
Plasma Membrane ◽  
Rat Liver ◽  
Rate Constant ◽  
Binding Constants ◽  
Compartmental Analysis ◽  
Insulin Binding ◽  
Bimodal Distribution ◽  
Subcellular Fractionation ◽  
Perfused Rat Liver ◽  
Binding Studies

This study utilizes the perfused rat liver combined with subcellular fractionation and compartmental analysis to investigate the effects of ethanol on hepatic uptake, endocytosis, and processing of insulin. At 4 min after the start of a 2-min pulse of radiolabeled insulin, increasing ethanol concentrations progressively inhibited insulin uptake by the liver (57% at 50 mM ethanol). Subcellular fractionation of the perfused livers showed a progressive shift in distribution from a predominantly endosomal location (control) to a bimodal distribution between endosomes and plasma membrane. This could be largely accounted for by a specific reduction in the endosome-associated insulin. Binding studies showed no changes in the binding properties of the plasma membrane insulin receptor. Compartmental analysis of the perfusate efflux curves confirmed the lack of effect of ethanol on the binding constants but showed a significant decrease in the endocytic rate constant (50%) together with an increase in the retroendocytic rate constant (33%). Simulation studies with the compartmental model showed that these changes could account for the observed decrease in uptake by the liver. No changes were found in the subsequent endocytic degradation of insulin.

Binding and Uptake of 125Iodine-Labelled, Oxidized Low Density Lipoprotein by Macrophages: Comparism of the Effects of a-Tocopherol, Probucol, Pyridoxal-5'-phosphate and Magnesium-pyridoxal-5'-phosphate-glutamate

1997 ◽  
Vol 52 (1-2) ◽  
pp. 97-104 ◽  
Author(s):  
Daniela Selmer ◽  
Reingard Senekowitsch-Schmidtke ◽  
W. Schneider ◽  
E. F. Elstner
Keyword(s):  
Specific Binding ◽  
Low Density Lipoprotein ◽  
Scavenger Receptor ◽  
Density Lipoprotein ◽  
Low Density ◽  
Protective Effects ◽  
Oxidized Low Density Lipoprotein ◽  
Unspecific Binding

Abstract Specific and unspecific binding and uptake (internalization) by macrophages of 125iodine -labelled, copper-oxidized human low density lipoprotein is differently influenced by the anti­ oxidants α-tocopherol (α-Toc), probucol (Prob), pyridoxal-5'-phosphate (PP) and the magnesium-pyridoxal-5'-phosphate glutamate complex (MPPG). Binding as well as internalization, mediated by the so-called "scavenger receptor" is lower in the presence of MPPG whereas both specific binding and internalization are enhanced. The comparison of the effects in vitro allows a rating of the potentially anti-atherogenic and thus protective effects of the tested substances as follows: MPPG > PP > α-Toc > Prob.

The galactose-specific receptor system in rat liver during development

Development ◽  
1987 ◽  
Vol 100 (1) ◽  
pp. 13-22
Author(s):  
L. Dini ◽  
L. Conti-Devirgiliis ◽  
S. Russo-Caia
Keyword(s):  
Endothelial Cells ◽  
Ligand Binding ◽  
Rat Liver ◽  
Binding Capacity ◽  
Specific Binding ◽  
Cell Types ◽  
Receptor System ◽  
In Situ Experiments

The number and distribution of galactose-specific binding sites were investigated in rat liver cells during perinatal development. Ligand binding to hepatocytes, macrophages and endothelial cells was followed with in vitro and in situ experiments by electron microscopy, using lactosylated bovine serum albumin adsorbed onto 5 nm colloidal gold particles as ligand. Binding capacity, starting at a late stage of fetal development, is very low both on the hepatocyte and on the macrophage surface, which show single particles statistically distributed. By contrast, bound particles are absent from fetal endothelial cells, which also lack the typical coated regions. In vivo, experiments at 37 degrees C show that endocytosis occurs to some extent in prenatal life. These results indicate that the expression of galactose-specific receptors' activity on the different liver cell types follows different developmental patterns, which are independently modulated.

scholarly journals The Mac-2 antigen is a galactose-specific lectin that binds IgE.

1989 ◽  
Vol 170 (6) ◽  
pp. 1959-1972 ◽  
Author(s):  
B J Cherayil ◽  
S J Weiner ◽  
S Pillai
Keyword(s):  
Transmembrane Domain ◽  
Binding Protein ◽  
Subcellular Fractionation ◽  
Carbohydrate Binding ◽  
Expression Library ◽  
Binding Properties ◽  
Extracellular Medium ◽  
Ige Binding ◽  
Alternatively Spliced

A cDNA encoding the Mac-2 antigen, a surface marker highly expressed by thioglycollate-elicited macrophages, has been cloned by immunoscreening of a lambda gt11-P388D1 expression library. The nucleotide sequence of the cDNA is identical to that of carbohydrate-binding protein 35, a galactose-specific lectin found in fibroblasts and highly homologous to a rat IgE-binding protein from basophilic leukemia cells. The in vitro synthesized Mac-2 protein displayed the expected carbohydrate- and IgE-binding properties. By pulse-chase analysis and subcellular fractionation studies, the Mac-2 protein was found in the cytosol but was also seen to accumulate in the extracellular medium. The latter finding was surprising in view of the fact that the cDNA did not encode a signal peptide or transmembrane domain. An alternatively spliced cDNA with the potential to encode a NH2 terminally extended Mac-2 protein with a stretch of hydrophobic amino acids at its NH2 terminus was also found, but it is not clear whether it is the source of the extracellular Mac-2. Possible functions for the Mac-2 protein based on its lectin- and IgE-binding properties are discussed.

Sign in / Sign up

Export Citation Format

Share Document