A clonal cell line of mouse neuroblastoma cells was found to undergo morphological differentiation in the presence of a K+ ionophore, valinomycin, in the assay medium. This effect was blocked by increasing the concentration of KCl of the medium, suggesting that the changes in resting membrane potential and ion fluxes may be involved in the mechanism of the formation of neurites. No enhancement of the neurite formation was observed in salines containing high concentrations of KCl in the absence of valinomycin. Depolarizing agents including veratridine, gramicidin and ouabain did not stimulate the outgrowth of neurites. Neither electrophoretic mobility of the cells nor molecular anisotropy of fluorescence probes in the membranes was modified by the treatment of valinomycin. Instead, it modified the slow binding phase in kinetics of the interaction of 1-anilinonaphthalene-8-sulfonate (ANS) with the cells, which is related to the penetration process of the probe into membranes. Valinomycin also enhanced the fluorescence intensity of ANS by increasing the binding sites in neuroblastoma cells. 相似文献
7β,8α-Dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BP diolepoxide, ) and 1-pyrenyloxirane () bind chemically to calf thymus DNA. The fluorescence efficiency of pyrenyl groups in mutagen modified DNA varies appreciably with its conformation and decreases in the order: pyrenees, modified denatured DNA and modified native DNA. A particularly interesting observation is that the fluorescence efficiency of mutagen modified DNA intensifies substantially upon denaturation. Our results suggest that the pyrenyl groups in mutagen modified DNA are intercalated between the base pairs of DNA. Since both and are powerful frame-shifting mutagens for S. typhimurium TA-98, the intercalative covalent binding of these compounds to DNA may provide a molecular basis for their mutagenic activity. 相似文献
The frequency of surviving colonies in two V79 cell lines exposed to either 6-thioguanine or 8-azaguanine was dependent on initial plating density. Different degrees of metabolic-co-operation were found to occur in the two cell lines and the loss of both spontaneous and added mutants occurred at a lower cell density when 6TG was used for selection than when 8 AZ was used in both cell lines. Both analogues were degraded on incubation in medium plus serum in the absence of added cells. Variation in serum batch had little effect on the rate of degradation or on the frequency of colonies recovered after treatment of V79 cell lines with 8AZ. The reasons for preferring 8AZ to 6TG as a selective agent are discussed. 相似文献
We have previously reported that lymphocytes from W/Fu rats immunized with syngeneic (C58NT)D tumor cells were cytotoxic against these cells in a 4-hr 51Cr release assay. We have investigated the feasibility of cryopreserving lymphocytes and target cells and have selected freezing conditions which provide good yields of viable cells and functional activity. Lymphocytes from different animals had a recovery of 60–80% viability which resulted in a corresponding 55–75% recovery of cytotoxic activity. Repeated testing of lymphocyte cytotoxicity from a pool of frozen spleen cells against either fresh or frozen (C58NT)D cells gave reproducible cytotoxicity. In addition, recovery of high levels of lymphocyte function was also demonstrated when cryopreserved cells were employed in long-term cytotoxic assays, i.e., 3H-proline and 125IUdR release assays, in the lymphoproliferative response to mitogens (PHA and Con A)3 or tumor cells (MLTI) as measured by 3H-thymidine incorporation, and in the in vitro generation of secondary cytotoxicity.By employing these cryoprotective techniques it is possible to have: 1) a population of lymphoid cells with known functional activity and 2) a pool of target cells with known susceptibility to lysis and antigenic content. Furthermore, the use of frozen cells as internal standards in each test also permits the analysis of assay variation as well as the study of variation in various cell types. 相似文献
Investigation has been made into the action of glucono--lactone on living cells of Pichia polymorpha in relation to the uptake of D-(U-14C) glucose, and the incorporation of (2-14C) uracil and L-(U-14C)-threonine into RNA and protein respectively. Other factors such as the action of glucono--lactone on cell morphology and on enzymic synthesis have also been studied. The action of this compound on -glucanase has been found to take place in the hydrolytic power and not in the synthesis. 相似文献
1. The uncoupler-stimulated ATPase activity of castor bean endosperm mitochondria and submitochondrial particles has been studied. The rate of ATP hydrolysis catalyzed by intact mitochondria was slow and little enhanced by addition of uncouplers at the concentration required for uncoupling the oxidative phosphorylation. ATPase activity was stimulated at higher concentrations of uncouplers.
2. 1-Anilinonaphthalene 8-sulfonate fluorescence was decreased when the mitochondria were oxidizing succinate. Carbonylcyanide-p-trifluoromethoxyphenylhydrazone and antimycin reversed the succinate-induced fluorescence diminution. ATP did not induce the fluorescence response.
3. The addition of succinate, NADH or ascorbate/N,N,N′,N′-tetramethyl-p-phenylenediamine as electron donor induced high ATPase activity in the presence of low concentrations of uncouplers. Stimulating effect of uncouplers was completely abolished by further addition of antimycin.
4. Submitochondrial particles were prepared by sonication. The particles catalyzed a rapid hydrolysis of ATP and carbonylcyanide-p-trifluoromethoxyphenylhydrazone at 10-8 M did not stimulate the ATPase activity. Addition of succinate induced uncoupler-stimulated ATPase activity. The effect of succinate was completely abolished by further addition of antimycin.
5. The treatment of submitochondrial particles by trypsin or high pH also induced uncoupler-stimulated ATPase activity.
6. The above results were interpreted to indicate that ATPase inhibitor regulated the back-flow reaction of mitochondrial oxidative phosphorylation. 相似文献
When observed over a temperature range, erythrocyte membrane lipids undergo a transition at 18–20 °C (Zimmer, G. and Shirmer, H. (1974) Biochim. Biophys. Acta 345, 314–320). This observation has prompted an investigation of the effects that substrate binding has on the transition of the red cell membrane. Glucose and sorbose were compared, since transport kinetics of these sugars still pose unresolved questions.In membranes, preloaded with glucose, the break at the transition temperature was intensified, while it was abolished or reversed in membranes preloaded with sorbose.These results were corroborated using different solubilization procedures (sonication, sodium dodecyl sulfate treatment) of the membranes, and also different techniques (viscosimetry, 90° light scattering, 1-anilino-naphthalene-8-sulfonate fluorescence).In extracted membrane lipids, viscosimetry indicated a break at transition temperature after preloading with either glucose or sorbose.Disc electrophoresis revealed a different binding pattern of the two sugars.It is suggested, that the amplification of the discontinuity in red cell membranes by glucose and the abolition or reversal of the break by sorbose are mediated by membrane protein- and/or membrane lipid-protein interaction. 相似文献
The mutagenicity of dimethylnitrosamine (DMN) to mammalian cells was investigated using a metabolic activation system. Mutation from 8-azaguanine (8AG) sensitivity to resistance in FM3A cells, a cell line derived from C3H mouse mammary carcinoma, was found only in the presence of dimethylnitrosamine, mouse liver microsomes and cofactors. The different inducibility of the mutation was shown by the use of liver microsomes from different strains of mouse. 相似文献