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971.
边缘性缺乏抗坏血酸之豚鼠,于三周内其肝脏及小肠粘膜3-羟-3-甲基戊二酰辅酶A还原酶(HMGR)活力均下降到原有水平的50%,但肝脏胆固醇7α-羟化酶活力尚无显著性改变。坏血病豚鼠(三周内)上述几种酶活力都下降至原有水平的50%左右。豚鼠摄取抗坏血酸不足,其血清总胆固醇浓度显著增加,而血清高密度脂蛋自胆固醇浓度显著减少,其改变程度与抗坏血酸缺乏状况一致。 相似文献
972.
Summary Expression of the anchorage-independent transformed phenotype in BHK 21/13 cells generally behaves as a recessive trait. When
chemically induced and spontaneously arising transformants are fused to the nontransformed parent line, transformation is
initially suppressed, reappearing after extended growth of the hybrids. In this paper, complementation for the expression
of anchorage independence was sought among a large group of such transformants, all independently derived from BHK 21/13 cells.
Tumorigenicity studies on selected hybrids and parental lines indicated that the in vitro trait of anchorage independence
is an accurate indicator of in vivo neoplasia for these cells. Seventeen of the 18 clones tested did not complement one or
more of three tester strains. This result indicates that anchorage independence arose in these clones as a result of lesions
in the same genetic function and suggests that the final step in the progressive changes of carcinogenesis may frequently
be restricted to lesions at a single locus.
This investigation was supported by National Institutes of Health grant CA27306. 相似文献
973.
Koji Yamada Masumi Ohtsu Genki Kimura 《In vitro cellular & developmental biology. Plant》1985,21(8):428-432
Summary Sodium butyrate causes proliferation arrest with a G2 (4C) DNA content and induces formation of tetraploid cells upon removal
of the inhibitor, in rat 3Y1 diploid fibroblasts. We isolated tetraploid clones from the butyrate-treated 3Y1 cells with high
efficiency; among 21 clones randomly isolated, 5 were pure diploid, 7 were mainly tetraploid with a small contaminating diploid
population, and 7 were pure tetraploid. Among the pure tetraploid clones, two showed doubled chromosome numbers with slightly
broader distributions than that seen in parental 3Y1 cells. Butyrate further induced polyploid formation in the tetraploid
cells thus produced, but octaploid cells that resulted could not be maintained for prolongeed, cultivation. We found no difference
between the tetraploid and the (parental and parallel isolated) diploid clones in terms of colony-forming ability, proliferation
rate, and sensitivity to density-dependent inhibition of proliferation. These results suggest that doubling of chromosome
number by itself does not cause a change in proliferation property. The tetraploid clones had lower average saturation densities
possibly due to enlargement of cell size represented by higher cellular protein content. 相似文献
974.
Robert T. Przygoda K. Takayama Karl A. Traul A. Tummey 《In vitro cellular & developmental biology. Plant》1985,21(1):32-38
Summary An atmosphere containing 10% CO2 has been generally accepted as optimal for the growth of Syrian hamster embryo cells in a clonal transformation assay. Data
presented in this paper show that 10% CO2 may not be the optimum environment for this assay.
Using 10 or 20% (analytically measured) CO2 in air (1 atm pressure), hamster embryo cell pools were examined for clonal growth characteristics and transformability using
five known carcinogens and a single noncarcinogenic compound. At 10% CO2, only 2 of 11 pools weee transformed by the five carcinogens but not by the noncarcinogen. At 20% CO2, six of seven pools were transformed by the five carcinogens and not by the noncarcinogen. Further, the transformation frequencies
were found to be greater in cultures incubated in an atmosphere consisting of 20% CO2 in air. The data also show that 20% CO2 increased the cloning efficiency of these cells.
A comparison of the 10 and 20% CO2 data to results reported from other conflicting interlaboratory results with this assay system may be due, in part, to variations
of CO2 concentrations. In some instances, the CO2 levels indicated by incubator flow meters vary considerably from analytically determined CO2 values. To prevent these CO2 discrepancies and their resultant effects on transformation and cloning efficiency, methods for monitoring the CO2 environment other than flow meters are recommended.
The observation of increased cloning efficiencies and transformation rates strongly suggests that culture incubation at 20%
CO2 is a preferred environment for the conduct of this assay. 相似文献
975.
Presence of theophylline and dibutyryl-cAMP—agents which cause elevation of intracellular levels of cAMP—in in vitro systems in which murine macrophages interact with virulent blood forms of Trypanosoma cruzi resulted in a marked inhibition of cell-parasite association (i.e., decreased surface binding and/or internalization). This effect was evidenced in terms of significant reductions in both the percentage of infected macrophages and the average number of trypanosomes per 100 macrophages. Pretreatment of the macrophages with these agents produced a similar inhibition whereas pretreatment of the parasites had no significant consequence on the interaction. The inhibitory effect was transient since it was no longer seen after 30 min of incubation of the treated macrophages in fresh medium. Thus, the inhibitory effect is exerted through a transient effect on the macrophage. 相似文献
976.
T-cell-mediated regression of "spontaneous" and of Epstein-Barr virus-induced B-cell transformation in vitro: studies with cyclosporin A 总被引:15,自引:0,他引:15
A B Rickinson M Rowe I J Hart Q Y Yao L E Henderson H Rabin M A Epstein 《Cellular immunology》1984,87(2):646-658
The regression of Epstein-Barr (EB) virus-transformed B-cell outgrowth which is seen in experimentally-infected cultures of blood mononuclear (UM) cells from healthy seropositive donors can be abolished in medium containing the T-cell-suppressive agent cyclosporin A (CSA) at concentrations of 0.05 microgram/ml and above. CSA mediates its effect within the first 4 days post-infection of the UM cells and this prevents subsequent in vitro generation of the EB virus-specific cytotoxic-T-cell response which normally brings about regression. Regression can be fully restored by supplementing the CSA-treated culture with interleukin 2 (IL-2)-containing culture supernatants or indeed with purified IL-2 itself, suggesting that CSA mediates its effect in this system through inhibiting the endogenous production of IL-2 which is required to amplify the virus-specific cytotoxic response. "Spontaneous transformation" to EB virus genome-positive lymphoblastoid cell lines in noninfected cultures of UM cells from healthy seropositive donors, though rare in normal medium, is enhanced to such a degree in the presence of CSA that, for many donors, the phenomenon becomes titratable against input cell dose across the 2.0 X 10(6)-2.5 X 10(5) cells/culture range. Cell mixing experiments suggest that the spontaneously transformed cell lines which arise with such efficiency under these conditions do so not by direct in vitro outgrowth of progenitor cells transformed by the virus in vivo, but by a two-step mechanism involving virus release and secondary infection in vitro. 相似文献
977.
Introduction of T-dependent antigens into the subarachnoid space (isas) resulted in higher systemic antibody responses in mice than injections into the peritoneal cavity (ip) or other sites commonly used for immunization. Antibody production in isas immunized mice was not increased by treatment with cyclophosphamide (Cy) at doses known to abolish T-suppressor-cell activity, but such treatment increased antibody production in ip immunized mice toward the higher level which was observed in the isas immunized animals. Suppressor cell-dependent low zone tolerance (LZT) to TNP-BSA could not be induced by isas injections of deaggregated BSA (d-BSA). Conversely, mice which were unresponsive to ip injected d-BSA showed consistent systemic antibody responses when the antigen was injected isas. These observations indicate that immune responses initiated within the CNS are associated with relatively ineffective induction of systemic suppressor cell activity. 相似文献
978.
N E Owen 《Biochemical and biophysical research communications》1984,125(2):500-508
The regulation of Na/K/Cl cotransport was investigated in vascular smooth muscle cells. That a Na/K/Cl cotransport system exists was established by the finding that the ouabain insensitive K influx was sensitive to the "loop" diuretic bumetanide. Furthermore, bumetanide sensitive K influx was dependent upon the presence of both Na and Cl in the extracellular milieu. Bumetanide sensitive K influx was inhibited by agents which elevate cellular cyclic AMP levels, and to a lesser extent by agents which elevate cellular cyclic GMP levels. When serum, EGF or TPA was added, bumetanide sensitive K influx was enhanced. These results suggest that vascular smooth muscle cells have a ouabain insensitive, bumetanide sensitive Na/K/Cl cotransport system which is stimulated by serum, EGF or TPA and inhibited by cAMP or cGMP. 相似文献
979.
Alan E. Levine David A. Hamilton Lynn C. Yeoman Harris Busch Michael G. Brattain 《Biochemical and biophysical research communications》1984,119(1):76-82
A polypeptide which inhibits the growth of human carcinoma cells has been characterized from Novikoff rat ascites fluid. This tumor inhibitory factor co-purified with transforming growth factor activity through acid/ethanol extraction and Bio-Gel chromatography. The two activities were completely separated by reverse phase HPLC. The tumor inhibitory factor is heat stable and requires disulfide bonds for bioactivity. This factor inhibited the anchorage independent growth of the more differentiated human colon carcinoma cell lines but did not affect the less differentiated carcinoma cells. The presence of stimulatory and inhibitory activities in the same extracts suggests that the relative concentrations of these factors may be important in the control of cell growth. 相似文献
980.
Q Q Zhuang S Rosenberg J Lawrence A Stracher 《Biochemical and biophysical research communications》1984,118(2):508-513
Actin binding protein from human blood platelets is shown to exist in the resting platelet as a phosphorylated protein and contains two residues of phosphate per 260,000 kd. Removal of one-half of these residues with E. coli alkaline phosphatase results in the loss of its ability to crosslink F-actin into a low speed sedimentable complex (its cytoskeleton) and to bind to an F-actin affinity column. Thus, phosphorylation-dephosphorylation of ABP may be an important regulatory mechanism by which the platelet regulates its shape via its cytoskeletal structure. 相似文献