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Biomedical subjects

P O Seglen

Publications and source records attributed to P O Seglen.

At least 145 records · Page 8Linked to original sources
PubMed1978

Effects of aminooxyacetate, alanine and other amino acids on protein synthesis in isolated rat hepatocytes.

Protein synthesis in isolated rat hepatocytes has been measured by the incorporation of [14C]valine at high concentration and constant specific activity (5 mmol/l and 315 muCi/l). Protein synthesis was stimulated by the addition of an amino acid mixture, and by a number of individual amino acids alone, most notably alanine. Energy substrates (lactate, pyruvate) stimulated protein synthesis to the same extent as alanine, suggesting that a major part of the amino acid effect could be due to the provision of energy. Aminooxyacetate, an inhibitor of glutamate transaminases, inhibited protein synthesis strongly (70%), and abolished the stimulatory effects of alanine and energy substrates. This could indicate that hepatocytic protein synthesis is subject to positive control by a transamination-dependent agent.

Amino Acids↗
PubMed1978

Effects of amino acids, ammonia and leupeptin on protein synthesis and degradation in isolated rat hepatocytes.

Protein synthesis in isolated rat hepatocytes, as measured by the incorporation of [14C]-valine at constant specific radioactivity, proceeded at a rate of 0.3-0.5%/h in an unsupplemented medium, i.e. only about one-tenth the rate of protein degradation (4%/h). Leupeptin, which inhibits lysosomal protein degradation (previously found to be 75% of the total degradation in hepatocytes), had no effect on protein synthesis, showing that endogenous protein degradation supplied amino acids in excess of the substrate requirements for protein synthesis. The inhibition of protein synthesis by NH4Cl (another inhibitor of lysosomal protein degradation) as well as the stimulation by a physiological amino acid mixture must therefore represent indirect effects, either on general energy metabolism, or on unknown regulatory processes.

Amino Acids↗
PubMed1978

Effect of temperature and divalent cations on the substratum attachment of rat hepatocytes in vitro.

The attachment of rat hepatocytes to polystyrene-adsorbed serum protein is relatively insensitive to inhibitors such as dextran sulphate, cycloheximide, colchicine and cytochalasin B, and enzymes like trypsin and neuraminidase, but it is strongly dependent on divalent cations. Mg2+ supports attachment better than Ca2+, but a combination of both is required for maximal attachment. The attachment is very temperature-sensitive, with a biphasic Arrhenius plot indicating an activation energy of 123 kJ/mol above 34 degrees C and 374 kJ/mol below 34 degrees C. The adsorbed attachment-promoting serum factor is inactivated by trypsin, or by Ca2+-dependent proteases which contaminate commercial preparations of collagenase. The adsorbed factor is resistant to treatment with glutaraldehyde, neuraminidase and heating to 90 degrees C, whereas the same factor in the unadsorbed state (in serum) is destroyed by heating to 70 degrees C. The factor in serum is unable to compete with the adsorbed factor for cell binding, hence it would appear that adsorption to polystyrene induces the active, heat-resistant conformation of the factor.

Animals↗
PubMed1977

Ammonia inhibits protein secretion in isolated rat hepatocytes.

The general secretion of proteins by isolated rat hepatocytes in suspension is inhibited by colchicine, anoxia, or ammonia (NH4Cl). The inhibition by ammonia is accompanied by the cytoplasmic retention and swelling of protein secretory vesicles, suggesting that ammonia accumulates in the vesicles and thereby prevents their translocation to the cell periphery. General protein synthesis appears to be relatively unaffected by ammonia.

Ammonia↗
PubMed1977

Protein-catabolic stage of isolated rat hepatocytes.

Isolated rat hepatocytes in suspension are in a protein-catabolic state (negative nitrogen balance), as measured by the continuous release of nitrogen in the form of amino acids and urea. The nitrogen loss corresponds to a protein degradation rate of 3-4% per h, while the rate of protein synthesis is negligible. Cells prepared from fasted, fed to regenerating livers are all highly protein-catabolic. The nitrogen balance is unaffected by insulin or amino acids (physiological mixture), and various metabolites and sera have only moderate effects. However, incubation of the cells for 2-4 h in a tissue culture medium (Dulbecco's) reduces the nitrogen loss dramatically, suggesting the formation of an anticatabolic factor under these conditions.

Amino Acids↗
PubMed1976

Incorporation of radioactive amino acids into protein in isolated rat hepatocytes.

The incorporation of radioactivity from a 14C-labelled amino acid mixture (algal protein hydrolysate) into protein in isolated rat hepatocytes has been studied. The incorporation rate declined with increasing cell concentration, an effect which could be explained partly by isotope consumption, partly (and largely) by isotope dilution due to the formation of non-labelled amino acids by the cells. At a high extracellular amino acid concentration, the rate of incorporation into protein became independent of cell concentration, because the isotope dilution effect was now quantitatively insignificant. The time course of protein labelling at various cells concentrations correlated better with the intracellular than with the extracellular amino acid specific activity, suggesting that amino acids for protein synthesis were taken from an intracellular pool. With increasing extracellular amino acid concentrations both the intracellular amino acid concentration, the intracellular radioactivity and the rate of incorporation into protein increased. Protein labelling exhibited a distinct time lag at high amino acid concentrations, presumably reflecting the time-dependent expansion of the intracellular amino acid pool. The gradual increase in the rate of protein labelling could be due either to an increased intracellular specific activity, or to a real stimulation of protein synthesis by amino acids, depending on whether the total intracellular amino acid pool or just the expandable compartment is the precursor pool for protein synthesis.

Amino Acids↗
PubMed1975

Mass isolation and culture of rat kupffer cells.

Collagenase perfusion of the liver followed by pronase treatment of the cell suspension thus obtained gave a quantitative recovery of viable nonparenchymal liver cells (NPC). From these NPC, Kupffer (K) cells can be purified by attachment to tissue culture dishes. Tail vein injection of carbon 1-2 h before liver perfusion permitted stepwise calculation as well as visualization of carbon-containing K cells. When these K cells have been put into tissue culture medium with serum and incubated overnight, they exhibit typical macrophage characteristics. Phase-contrast and transmission electron microscopy showed typical macrophage morphology and scanning electron microscopy revealed well-spread cells with cytoplasmic projections and ruffled membranes. Endocytosis studies using radioactive colloidal gold and inert latex particles also indicated that these cells are highly active in pinocytosis and phagocytosis. Further characterization of K cells is the identification of Fc receptor on their membranes. Studies on lysosomal enzymes showed that purified K cells possess higher specific activities in beta-glucuronidase, acid DNase, and cathepsin D than in purified parenchymal cells.

Animals↗