Scavenger lipoprotein receptors are more effective in ligand internalization than low density lipoprotein receptors in human monocyte-macrophages.

Human monocyte-macrophages in culture express specific receptors for low density lipoproteins (LDL receptor) and human acetylated LDL (AcLDL receptors or scavenger receptors). After 24 h in lipoprotein-deficient serum, the cells expressed 2-3 fold more AcLDL receptors than LDL receptors as measured by trypsin releasable radioactivity after exposure to 125I-LDL or 125I-AcLDL at 37 degrees C. The efficiency of intracellular ligand delivery by the two receptors was evaluated as an internalization index (defined as intracellular + degraded/bound ligand).

[Supracondylar and distal epiphyseal femur fractures in the dog and cat].

Various surgical methods for the treatment of supracondylar femoral fractures involving the epiphyseal growth plates in young growing dogs and cats were studied. Some of the open reduction and fixation techniques are briefly reviewed with emphasis on some of the complications that may develop in the stifle joint. Good results were obtained with the single Steinmann pin method in cats and small breeds of dogs.

Ascorbate increases the number of low density lipoprotein receptors in cultured arterial smooth muscle cells.

Receptor-mediated catabolism of low density lipoprotein (LDL) was increased 2-3-fold in down-regulated smooth muscle cells when the culture medium was supplemented with physiological concentrations of sodium ascorbate for 24 h. The enhanced degradation of LDL was associated with increased LDL receptor activity and LDL uptake. The increase in receptor activity was rapid, transient and inhibited by cycloheximide.

The degradation of endogenous and exogenous proteins in cultured smooth muscle cells.

The pathways of degradation followed by endogenous proteins in cultured smooth muscle cells were compared with the well-characterized lysosomal pathway involved in the degradation of apolipoprotein B of endocytosed LDL. Under conditions in which lysosomal activity towards 125I-labeled LDL was almost completely inhibited by chloroquine and/or ammonium chloride, the degradation of short-lived and abnormal proteins, assessed by the release of [3H]phenylalanine, was reduced by only 10-17%. The basal rate of degradation of long-lived proteins was reduced by about 30% by the same inhibitors while the accelerated proteolysis found under nutrient-poor conditions could be completely accounted for by the lysosomal system as defined by these lysosomotrophic agents.

Low density lipoprotein metabolism in cultured fibroblasts from a new group of patients presenting clinically with homozygous familial hypercholesterolemia.

The metabolism of low density lipoproteins (LDL) was studied in cultured fibroblasts obtained from five local patients diagnosed, on the basis of clinical features and serum cholesterol concentrations, as having the homozygous form of familial hypercholesterolemia. LDL receptor function was assessed by measuring the binding, internalization, and degradation of 125I-labeled LDL, and by measuring the stimulation of cellular acyl-CoA cholesterol acyltransferase (ACAT) activity which followed exposure to LDL. Fibroblasts from two cases (CF and GM) showed receptor activities which were approximately 10% of the values obtained with normal cells, while ACAT stimulation by LDL was very low.

Metabolism of cytoplasmic triacylglycerol in cultured aortic smooth muscle cells.

A turnover of cytoplasmic triacylglycerol was studied in cultured rat, rabbit, and bovine aortic smooth muscle cells. Cytoplasmic triacylglycerol was labeled with [3H]glycerol in the presence of oleic acid in the medium and its loss from the cell was studied in the presence of carrier glycerol. Multiple additions of Isuprel or dibutyryl cyclic AMP during the chase period did not enhance the loss of labeled triacylglycerol.

Retro-endocytosis of low density lipoprotein by cultured bovine aortic smooth muscle cells.

Cultured bovine aortic smooth muscle cells, pretreated with 125I-labelled low density lipoprotein (LDL), rapidly released significant amounts of the lipoprotein as trichloroacetic acid-precipitable material during a subsequent chase period. The time and temperature dependence of this release process and its insensitivity to heparin-pretreatment of equilibrated cells suggest that LDL was regurgitated from cells by a rapid process that we have termed 'retro-endocytosis'. The total amount of lipoprotein released from cells equilibrated at 37 degrees C with 125I-labelled LDL was approximately 20% of the amount degraded, pointing to the existence of a small pool of material which was distinct from the lysosomal pathway.

Degradation of apolipoprotein B of low density lipoprotein by cultured bovine smooth muscle cells. Accumulation of intermediates in the presence of protease inhibitors.

The incubation of bovine aortic smooth muscle cells with 125I-labeled low density lipoprotein in the presence of protease inhibitors resulted in the significant intracellular accumulation of intact apolipoprotein B, as well as a number of high molecular weight degradation intermediates. This effect was brought about both by leupeptin, a specific inhibitor of thiol proteases (40% inhibition of degradation), as well as by the more general lysosomotrophic inhibitors, chloroquine and NH4Cl. Qualitatively identical spectra of degradation intermediates were formed in the presence of chloroquine and NH4Cl as determined by autoradiography of SDS-polyacrylamide gel electrophoretic fractions, ranging from the apolipoprotein B band (Mr = 340,000) to bands with molecular weights of less than 14,000.

Modulation of cytoplasmic cholesteryl ester of smooth muscle cells in culture derived from rat, rabbit and bovine aorta.

Esterification of cholesterol in smooth muscle cells, isolated from rat, rabbit and bovine aorta, was achieved by incubation with cholesterol enriched medium containing [7(n)-3H]cholesterol. The newly formed cholesteryl ester was readily hydrolyzed when the cells were post-incubated with medium containing lipoprotein deficient serum. The rate of loss of labeled cholesteryl ester was not inhibited by the presence of 100 microM chloroquine.

Cathepsin-D-dependent initiation of the hydrolysis by lysosomal enzymes of apoprotein B from low-density lipoproteins.

The degradation of 135I-apoprotein B of human low-density lipoprotein by cell extracts of cultured bovine aortic smooth muscle cells was determined by measuring the formation of acid-soluble products and by analyzing the electrophoretic patterns of digested apoprotein in gels containing sodium dodecyl sulfate. Degradation resulted in an initial rapid accumulation of a limited number of distinct smaller fragments. Two products with apparent molecular weights of 220,000 and 200,000 predominated.

Plasmin-treated low density lipoproteins: polypeptide analyses and metabolism by cultured smooth muscle cells.

Plasmin, generated by the interaction of urokinase with plasminogen, degraded the apoprotein B moiety of human low density lipoprotein to yield distinct high moleculr weight intermediates under conditions where only a small fraction (less than 3%) of the protein was hydrolyzed to trichloroacetic acid-soluble products. The molecular weights of these intermediates were between 60 000 and 200 000 as estimated by SDS-polyacrylamide electrophoresis. Trypsin treatment yielded fragments of similar size to those obtained with plasmin.

Cardiac myofibrillar phosphorylation and adenosine triphosphatase activity.

When myofibrils from rat hearts were dissolved in concentrated salt solutions and reprecipitated by dilution, they contained both protein kinase (partly cyclic 3':5'-AMP-dependent) and protein phosphatase activities. Troponin-I was the major protein to be phosphorylated by the endogenous myofibril-associated kinase and by added protein kinase. Approximately 1 mole of phosphate per mole of troponin-I was incorporated from radioactive ATP, but the extent of troponin-I phosphorylation could be varied experimentally.

Uptake and degradation of low density lipoproteins (LDL) by confluent, contact-inhibited bovine and human endothelial cells exposed to physiological concentrations of LDL.

Metabolism of low density lipoproteins (LDL) was studied in cultures of endothelial cells derived from bovine aorta or heart and from human umbilical veins. At low LDL concentrations nonconfluent cultures of bovine endothelial cells catabolized more LDL protein than contact-inhibited confluent cultures but this difference was reduced at high LDL concentrations. Nonconfluent human endothelial cells displayed also a higher rate of LDL degradation than their contact-inhibited counterparts, but this difference was less pronounced than in the bovine cells.

Modulation by sodium ascorbate of the effect of chloroquine on low density lipoprotein retention and degradation in cultured human skin fibroblasts.

Human skin fibroblasts in culture were incubated for 48 h with 125I-labelled low density lipoprotein and chloroquine in the presence and absence of sodium ascorbate. Pretreatment of the cells for 3 days with sodium ascorbate and addition of the vitamin during incubation resulted in a decrease in cellular retention and an increase in degradation of the labelled low density lipoprotein. Similar results were obtained when the cells were pretreated for 3 days but the vitamin was not added during the final 48 h of incubation.

5-bromo-2'-deoxyuridine-stimulated calcium ion- or magnesium ion-dependent ecto-(adenosine triphosphatase) activity of cultured hamster cardiac cells.

1. Treatment of hamster heart cells in primary culture with 5-bromo-2'-deoxyuridine resulted in the greatly increased activity of a particulate Ca2+- or Mg2+-dependent ATPase (adenosine triphosphatase). 2.

Effects of 5-bromo-2'-deoxyuridine on beating heart cell cultures from neonatal hamsters.

1. Primary heart cell cultures from neonatal hamsters yielded a heterogeneous cell population, containing muscle cells undergoing progressive differentiation, as well as non-muscle cells. 2.