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Biomedical subjects

O Stein

Publications and source records attributed to O Stein.

At least 163 records · Page 9Linked to original sources
PubMed1976

Ultrastructural localization of concanavalin A in the perfused rat heart.

Staining of the surface coat of heart capillaries and aorta was achieved by perfusing concanavalin A and phytohemagglutinin coupled to horseradish peroxidase through the rat heart. The binding of these lectins provides evidence for the presence of glycoproteins containing mannose, glucose, and N-acetylgalactosamine residues in the endothelial surface coat of rat aorta and heart capillaries. The binding of concanavalin A to capillary endothelium was further followed with radioautography of 125I-labeled concanavalin A in the in vitro perfused rat heart. Following the shorter time intervals of perfusion more than 80 per cent of labeled concanavalin A was releasable by alpha-methyl-D-mannoside and the radioautographic reaction was confined to the endothelial cell surface. Following 60 minutes of perfusion with concanavalin A there was translocation of part of the lectin to the extravascular space and evidence of endothelial cell swelling. A tentative estimate of the concanavalin A binding sites in capillary endothelium was determined to be approximately 5000 per sq. mum.

Animals↗
PubMed1975

A comparative study on the removal of cellular lipids from Landschütz ascites cells by human plasma apolipoproteins.

The effects of human plasma lipoprotein-proteins on the removal of cellular lipids from Landschütz ascites cells were studied. Cellular lipids were labeled by injecting mice previously injected with ascites with either [3H]cholesterol or [3H]choline. Apoproteins from very low density (apoC-I, C-II, and C-111) and high density (apoA-I and A-II) lipoproteins were used. Each of the apoproteins alone was ineffective in removing cellular [3H]cholesterol. However, when synthetic phosphatidylcholines of known composition were added to each apoprotein and the experiments were repeated using either apoprotein-lipid mixtures or ultracentrifugally isolated complexes, the removal of sterol was considerably enhanced. Complexes of saturated phosphatidylcholines with apoA-II, apoC-I, or apoC-III were the most effective in releasing cellular sterol. Apoprotein-phospholipid complexes were much less effective in removing cellular [3H]phosphatidylcholine than the free apoproteins; apoA-I and apoC-I were the best of the five apoproteins studied. When a comparison was made of the adsorption of iodinated apoproteins to ascites cells, 3 to 4 times more apoA-II and apoC-III were bound than apoA-I. The binding of apoproteins was time and temperature dependent. Approximately 50% of the radioactivity that remained in the washed cells was removed with trypsin. To determine if the counts remaining in the trypsin-treated cells were internalized, identical experiments were performed using human erythrocytes, cells that do not exhibit pinocytosis. Again, approximately 50% of the radioactivity of the iodinated apoproteins was not released by trypsin. Succinylation of apoA-II not only destroys its phospholipid-binding properties but also its adsorption to red cells. These results suggest that the plasma apoproteins differ in their ability to remove cellular lipids and bind to both ascites and red cell membranes, and possibly to specific phospholipids, in such a way that only a part of the apoprotein is degraded with proteases.

Apoproteins↗
PubMed1975

Surface binding and interiorization of homologous and heterologous serum lipoproteins by rat aortic smooth muscle cells in culture.

Rat aortic smooth muscle cells in culture were incubated with rat or human iodinated low and high density lipoprotein at 5-50 mug/ml for 3 h. With the homologous lipoproteins, 25-49% of total cellular protein radioactivity was trypsin releasable and was considered as surface-bound radioactivity, while the balance represented cellular uptake. The ratio of surface-bound to cellular label was higher when the cells were incubated with human lipoproteins and was about 9 : 1 with human high density lipoprotein. Cellular uptake of rat low density lipoprotein was about twice that of rat high density lipoprotein, while degradation of labeled protein, which had presumably followed protein uptake, was similar and ranged from 20 to 25% of protein uptake in 3 h. Experiments designed to test the effect of cell density on lipoprotein uptake have shown that the uptake was related inversely to cell density. Thus, the lower lipoprotein uptake encountered in the rat smooth muscle cells, compared to that described for human fibroblasts (Goldstein, J.L. and Brown, M.S. (1974) J. Biol. Chem. 249, 5153-5162), could be due in part to the much lower cell density used in the latter studies, as well as to cell type and species difference.

Animals↗
PubMed1975

Interference with the transport of heparin-releasable lipoprotein lipase in the perfused rat heart by colchicine and vinblastine.

The effect of pretreatment with colchicine or vinblastine on the lipoprotein lipase activity of rat heart was studied. Administration of colchicine or vinblastine 4 h prior to perfusion of the heart caused a very marked reduction in lipoprotein lipase activity released into the perfusate within 1 min of heparin perfusion. At the same time an increase in residual heart lipase occurred so that total lipoprotein lipase content of the heart (heparin releasable plus residual) did not change. The colchicine effect was dose and time dependent; no decrease in heparin-releasable enzyme activity occurred after only 30 min of pretreatment or upon addition of colchicine into the perfusate. These results indicate that colchicine did not impede enzyme synthesis or its release from the cell surface, but may have interfered with the transport of lipoprotein lipase from the site of its synthesis to the endothelial cell surface.

Animals↗
PubMed1975

The removal of cholesterol from aortic smooth muscle cells in culture and Landschutz ascites cells by fractions of human high-density apolipoprotein.

Ascites cells were labeled by intraperitoneal injection of [3H]cholesterol and aortic smooth muscle cells by addition of [3H]cholesterol to the serum component of the culture medium. The release of cholesterol from cells into a serum-free medium supplemented with the various "acceptors" was studied using ascites cells in suspension and aortic smooth muscle cells in a multilayer culture. Unfractionated human high-density apolipoprotein was somewhat more effective in the removal of labeled cellular free cholesterol, in both cell types, than apolipoprotein derived from rat high-density lipoprotein. Following separation of human high-density apolipoprotein into four fractions by Sephadex chromatography, the effect of each fraction on the removal of cellular cholesterol from ascites cells was studied. The individual fractions had a lower capacity for cholesterol removal than the original unfractionated high-density apolipoprotein and the lowest activity was detected in Fraction II which comprised 75% of the total apolipoprotein. The effectiveness to remove cholesterol could be restored to all the fractions, as well as enhanced, by addition of sonicated suspensions of lecithin or sphingomyelin, which by themselves promoted a more limited removal of cellular cholesterol. Negatively stained preparations of mixtures of the four fractions and sonicated dispersion of lecithin were shown to consist of vesicles and discs of various sizes. Addition of the apolipoprotein fractions (especially Fractions II and IV) to sonicated dispersion of sphingomyelin resulted in a pronounced formation of discs which showed a high tendency towards stack formation. Mixtures of Fraction II and lecithin or sphingomyelin were effective in the release of cellular cholesterol from multilayers of aortic smooth muscle cells in culture. These results show the feasibility of net removal of cholesterol from cells which grow in a form resembling a tissue and thus provide a model to study the role of apolipoprotein-phospholipid mixtures in cholesterol removal from cells and tissues in vivo.

Animals↗
PubMed1975

Colchicine-induced inhibition of plasma lipoprotein lipase release in the intact rat.

The release of plasma lipoprotein lipase by heparin was studied in fed and food-deprived rats pretreated with colchicine and vinblastine. Four hours after the administration of either drug the lipoprotein lipase activity released by heparin was only half of that found in controls. Colchicine affected the release of both protamine-sensitive and protamine-resistant lipoprotein lipase. It is suggested that colchicine and vinblastine interfere with the transport of lipoprotein lipase from the site of its storage to the vascular cell surface.

Animals↗
PubMed1975

Turnover of phospholipids in rat aortic smooth muscle cells in culture.

Smooth muscle cells derived from rat aortic media were explanted and grown in culture for 14 to 60 days. During that time they formed a confluent multilayer and depostied extracellular material resembling newly formed elastin. The lipid composition of the cells in culture differed slightly from the parent cells in the intact aorta with respect to a higher phospholipid/DNA ratio and a higher lecithin content. The cholesterol content resembled that of parent cells. After incubation with labeled precursor the cultured cells show an active lipid synthesis; choline is incorporated mainly into lecithin, whereas glycerol and palmitate appear in phospholipids and to a lesser extent in neutral lipids. After a 2 hour pulse and up to 96 hour chase there is a linear fall in the specific acitivty of lecithin with a half-time of 28 to 30 hours. The rate of fall in specific activity of glycerol- or choline-labeled lecithin was found to be similar, indicating that choline does not turn over by an exchange reaction and is a suitable marker for studying phospholipid turnover in cultured cells. The results provide a basis for investigation of the effect of increasing cellular cholesterol content on phospholipid turnover.

Animals↗
PubMed1975

Comparative uptake of rat and human serum low-density and high-density lipoproteins by rat aortic smooth muscle cells in culture.

Rat aortic smooth muscle cells in culture were exposed to rat and human serum (LDL) and high-density (HDL) lipoproteins labeled with 125-I. 125-I-lipid was taken up preferentially from all of the lipoproteins used. 125-I-protein uptake of both rat LDL and HDL was significantly higher than that of the corresponding human lipoproteins, and human LDL was preferred to human HDL. The uptake of delipidated high-density apolipoproteins of either rat or human origin was very low. About 3-4% of the interiorized rat LDL and HDL was catabolized during 48 hours of incubation. On electron microscopic autoradiography of cells incubated with rat 125-I-LDL, the concentration of label, representing mainly 125-I-protein, was associated with secondary lysosomes. These results suggest that, if the protein uptake represents particle uptake, the preferential uptake of human LDL compared with human HDL could account in part for the finding that LDL acts as a more potent feedback suppressor of 3-hydroxy-3-methylglutaryl CoA reductase than does HDL.

Alcohol Oxidoreductases↗
PubMed1975

Radioiodinated lipoproteins: absorption of 125I radioactivity by high density solutions.

Concentrations of potassium bromide commonly used for separation of lipoproteins were shown to cause absorption of 125I and thus reduce the counting efficiency of the labeled lipoproteins. Chloroform was shown to cause a 50% reduction in counting efficiency of lipid from 125I-labeled lipoprotein. No reduction of counting efficiency was observed in the presence of high density solutions when 131I was used as label.

Animals↗
PubMed1974

Colchicine-induced inhibition of lipoprotein and protein secretion into the serum and lack of interference with secretion of biliary phospholipids and cholesterol by rat liver in vivo.

Rats were injected with colchicine and the secretion of triglycerides into the serum was studied for 90 min after injection of [(14)C]palmitic acid and Triton WR 1339. The release of labeled and chemically determined triglyceride was reduced to about 20-30% of control values. The effect of colchicine on serum triglyceride levels was not dependent on the presence of Triton and was similar in males and females and in fed and fasted rats. The effect was dose dependent and was reversible 6-7 h after injection of 0.05 mg/100 g body weight. Colchicine inhibited also the release of labeled proteins into the serum but did not affect the amount of [(3)H]leucine incorporated into liver proteins. Within 4 h of colchicine treatment there was an 80% fall in serum very low density lipoproteins (VLDL), a 30% fall in serum high density lipoproteins (HDL), and no change in the d > 1.21 protein level, but reduction in the appearance of labeled proteins was encountered in all serum fractions. Colchicine had no effect on the rate of bile flow and on the secretion of phospholipids and cholesterol into the bile. In the hepatocyte there was accumulation of Golgi-derived secretory vesicles, containing nascent VLDL particles; these vesicles were seen also in the vicinity of the sinusoidal cell surface, but the space of Disse contained few or no VLDL particles. There was an apparent reduction in microtubules and some increase in microfilaments. It is suggested that microtubules affect the secretion of lipoproteins and proteins into the serum by maintaining the organization of the plasma membrane required for its fusion with secretory vesicles. The lack of effect of colchicine on biliary lipid secretion indicates that the latter is not dependent on vesicular transport.

Animals↗