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Biomedical subjects

L Warren

Publications and source records attributed to L Warren.

100 records · Page 6Linked to original sources
PubMed1969

Membranes of animal cells. 3. Amino acid incorporation by isolated surface membranes.

Surface membranes isolated from mouse fibroblasts contain RNA organized in ribosome-like particles. These surface membranes can incorporate radioactive amino acids into material insoluble in hot trichloroacetic acid. Characterization of the radioactive products indicated that they are large polypeptides. Most requirements and inhibitors of the system were similar to those of the microsomal system of the endoplasmic reticulum. Further comparisons were made with microsomal and pH 5 fractions prepared from L-cells by standard procedures and by two methods attempting to simulate the conditions necessary for isolating surface membranes. The amount of L-leucine incorporated by the surface membranes per mg of RNA was comparable to the values obtained by the microsomal and pH 5 fractions prepared by standard procedures. In contrast, the activity of the two other microsomal fractions was less than 10 per cent of this amount. The most striking difference noted was in the products formed by the surface membranes and by the microsomal systems. These products were demonstrated to be quite different by electrophoresis on acrylamide gels. It is suggested that the surface membranes participate actively in protein synthesis in vivo, and that, because of this location, the protein-synthesizing mechanism may be able to perform special functions more efficiently.

Amino Acids↗
PubMed1968

Membranes of animal cells. II. The metabolism and turnover of the surface membrane.

Turnover studies of the surface membrane and of cell particulate matter of L cells in tissue culture in logarithmic and plateau phase of growth have been made. The rate of incorporation of isotope into these fractions and the rate of fall of specific activities of labeled L-cell fractions have been observed. The following interpretation of the data appears most likely although other interpretations are possible. Growing and nongrowing cells synthesize approximately similar amounts of surface membrane and particulate material. In the growing cell the material is incorporated with net increases in substance. There is relatively little turnover. In the nongrowing cell newly synthesized material is incorporated, but a corresponding amount of material is eliminated so that there is turnover without net increase of substance. Our results suggest that there is no gross differential turnover between the protein, lipid, and carbohydrate of the surface membrane under the conditions of our experiments. Metabolic inhibitors or omission of amino acids in the culture medium lead to a decrease in synthesis of surface membrane and cell particulates and cause an equivalent decrease in the rate of degradation of surface membrane and of particulates; therefore the synthetic and degradative aspects of turnover appear to be coupled. As cultures of nongrowing cells in suspension or on a glass surface age, their synthetic and turnover capacities diminish. Our results suggest that the cell may exist in a nongrowing state with a level of synthesis similar to that of a growing cell. It can exist in this state with a high level of turnover.

Amino Acids↗
PubMedDate not supplied

Cystic fibrosis: an alternative approach.

Sometimes hospital is the best place for patients with cystic fibrosis, says Lyz Warren. Here she describes the choices available to children and parents on a unit which follows the philosophy adopted by The Children's Trust.

Adolescent↗
PubMedDate not supplied

Alterations of vinblastine influx in multidrug-resistant lymphoblastic leukaemic CEM cells.

Typical multidrug-resistant (MDR) CEM/VLB100 cells exhibited reduced uptake of vinblastine (VLB) compared to their sensitive CEM counterparts mean results were respectively, 3.19 and 35.4 pmol per 10(6) cells. In CEM cells, the efflux of drug reached a steady state after 10-15 min while in CEM/VLB100 cells, the typical P170-mediated efflux was still efficient after 40 min. Nevertheless, the most striking difference observed in CEM/VLB100 cells was a dramatic decrease in early (30 sec) influx of drug which was 10 times lower than in sensitive cells, a characteristic still observed in the presence of Na azide and absence of glucose. MDR cells without little or no effect on sensitive cells. The Q10 entry of VLB into sensitive cells was 1.2 while it was 2.2 in CEM, suggesting that the mode of entry of VLB into MDR cells differed from that of CEM cells. Verapamil or nigericin, which rapidly increased the accumulation of VLB raised the Q10 to >2. These results suggest that the primary defect in MDR cells would be an inhibition of influx, which might involve interactions with P170 through a reversible process.

Drug Resistance, Multiple↗