摘要:

AbstractChanges in the mechanisms of folate incorporation were studied in cells treated with low concentrations of methotrexate in order to evaluate their contribution to the development of resistance to antifolate drugs. The uptake of methotrexate via reduced‐folate system, the membrane‐associated high‐affinity folate binding capacity and the activity, levels and affinity for methotrexate of dihydrofolate reductase were measured in L5178 murine leukemic lymphoblasts and in a subline, MTX/R16, 16 times more resistant to methotrexate which was isolated after a short exposure to the antifolate. Various simultaneous changes were characterized in MTX/R16 cells which co‐participated in the development of resistance: a decreased affinity of the carrier for methotrexate uptake via the reduced‐folate system of entry, the increase of dihydrofolate reductase activity and levels and a two‐fold increased expression of a membrane‐associated high‐affinity folate‐binding protein (mFBP). The increase of the mFBP expression, besides ensuring the growth of resistant cells by its contribution to the reduced folate intake, also participates in the methotrexate resistance by the internalization of folate cofactor which would compete with methotrexate hindering the effective inhibition of dihydrofolate reductase

ISSN:0263-6484    

DOI:10.1002/cbf.290100102

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe cellular resistance to cytotoxic drugs, particularly to anthracyclines, remains a major problem in cancer chemotherapy. A number of biochemical mechanisms have been described, one of them being a lower accumulation of drugs in resistant cells. The accumulation of Ho33342 in sensitive and resistant Friend leukemia cells was studied by quantitative fluorescence image analysis, a method which allows investigations to be made on living tissues and cells. The intensity of fluorescence is related to the amount of Ho33342 accumulated into the cells and has been found to be more intense in sensitive cells than in resistant ones. Moreover, the retention of this vital dye was inversely related to the degree of resistance in the three resistant cell lines. The addition of verapamil, which is known to reverse resistance to anthracyclines, resulted in an increase of the amount of Ho33342 accumulated in the resistant cells. Ho33342 presents a higher quantum yield than any other anthracyclines, such as adriamycin and can be used as a microfluorimetric probe to identify the resistant cells in a heterogeneous cell population.

ISSN:0263-6484    

DOI:10.1002/cbf.290100103

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe molecular structure of aldehydes is closely related to their antimicrotubular effect. Morphological modifications of the microtubular system in living cells after incubation with certain aldehydes are consistent with biochemical alterations detected in previous research. The microtubular arrangement was visualized by an immunofluorescence technique with antitubulin antibodies, while the content of tubulin in the cells was evaluated by a colchicine binding assay. 2‐Nonenal behaved similarly to 4‐hydroxynonenal, a lipid peroxidation product, disorganizing microtubular network in 3T3 fibroblasts and decreasing the amounts of tubulin able to bind labelled colchicine. Nonanal did not significantly impair the tubulin characteristics in the cells, despite the fact that it has been shown to be active on the purified microtubular system; benzaldehyde was ineffective. This would appear to explain the mechanisms of interaction of aliphatic aldehydes which might be suitable for use as antimicrotubular dr

ISSN:0263-6484    

DOI:10.1002/cbf.290100104

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe aim of this work was to study the metabolic activity in isolated hepatocytes from control rats and rats exposed for 15 or 30 days to cold, all subjected to 24‐h fasting. Hepatocyte oxygen consumption was used as an index of metabolic activity. The results show that 24‐h fasting induces a decrease in energy expenditure at the level of the liver in cold‐exposed rats but not in control an

ISSN:0263-6484    

DOI:10.1002/cbf.290100105

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractNa‐metavanadate and ouabain that act on Na+K+‐ATPase had no influence on insulin binding toTetrahymenaimmediately after treatment, but after 24 h considerably enhanced the binding capacity of generations of progeny. The increase in binding was of a similar magnitude to that elicited by insulin imprinting. Vanadate failed to increase the imprinting potential of insulin while ouabain even prevented insulin imprinting when administered together with insulin, but, did not affect imprinting when administered after insulin. By analogy with higher organisms it appears that inhibition of Na+K+‐ATPase plays no role in the insulin‐like effect of vanadate on the unicellularTetrahymena, as judged also from the capacity to bind insulin of the generations of of

ISSN:0263-6484    

DOI:10.1002/cbf.290100106

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractProtamine induces a gradual change in plasma membrane permeability in rabbit neutrophils, which is evident from the increase of indol fluorescence, and the leakage of quin2 from quin2‐loaded neutrophils. The influx of extracellular Ca2+into the neutrophil provides an explanation for exocytosis which occurs in the presence of Ca2+and protamine. The dependence of exocytosis on Ca2+concentration follows the same pattern as is observed in neutrophils permeabilized by other means. In the absence of Ca2+, and in the presence of protamine, La3+has an activating effect on exocytosis. At higher concentrations La3+inhibits exocytosis that occurs in the presence of Ca2+and protamine, as do some other metal ions. The resemblance between the membrane effects of a number of toxins, as reported in literature, and protamine‐induced membrane damage suggests that they occur via the same mechan

ISSN:0263-6484    

DOI:10.1002/cbf.290100107

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have previously shown that inhibitors ofN‐glycan processing alter both the cell surface carbohydrates and the homing properties in lymphoid cells. We have now studied the effects of the ionophore monensin (MON) on these parameters.Arrest in the spleen of [111In]‐labelled BL/VL3 murine T lymphoma cells, injected intravenously was clearly reduced if the cells had been cultured for 24 h in the presence of monensin (0·1–1·0 μg ml−1).We have characterized glycopeptides from BL/VL3 murine T lymphoma cells. Following labelling with tritiated precursors (fucose, mannose, galactose, glucosamine), surface glycopeptides from BL/VL3 murine T lymphoma cells, were released by trypsin and separated by gel filtration on Bio‐Gel P6 and by affinity chromatography on immobilized lectins.After treatment with MON, a class of high molecular mass glycopeptides was no longer found. There were less complex and more high mannose glycans, as a consequence of a reduction of terminal glycosylation (sialylation, fucosylation or incorporation ofN‐acetyl‐glucosamine). Similar findings were obtained with immunoprecipitated Thy‐1 antigen. However, as estimated by flow cytometry analysis, the cell surface expression of Thy‐1 was not reduced in MON‐treated cells. Taken together our results show that cell surface oligosaccharides are modified dramatically, but that at least, certain cell surface antigens are present in normal amounts. It is tempting to speculate that changes in glycosylation account for the abnormal homing propertie

ISSN:0263-6484    

DOI:10.1002/cbf.290100108

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractIn response to concanavalin A, cytoplasmic calcium movement was observed in human platelets, both in the presence of 1 mM Ca2+or 1 mM EGTA in the medium. Concanavalin A also caused the activation of inositide turnover and the production of inositol phosphates, suggesting that activation of phospholipase C occurs. The mechanism by which concanavalin A stimulates phospholipase C does not depend on GTP‐binding transducers, because it was not inhibited by GDPβS, while experiments performed in the presence of cytochalasin B suggested a role for membrane glycoprotein IIb‐IIIa‐cytoskeleton interaction in this process. Ca2+‐proteases and Na+/H+antiport also seemed to be related to concanavalin A‐induced phospholipase C activation, as suggested by experiments performed in the presence of leupeptin and

ISSN:0263-6484    

DOI:10.1002/cbf.290100109

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractA balance of ATP‐consuming processes in human erythroleukemia (K 562) cells by use of the decreased14CO2formation from [1‐14C]‐glutamate following inhibition of energy‐requiring processes is presented. This method was tested on Ehrlich mouse ascites tumour cells and was used in suspensions of K 562 cells with a low cell content. More than 90 per cent of the ATP produced by oxidative phosphorylation could be accounted for in K 562 cells. Protein synthesis consumed about 35 per cent, Na+/K+‐ATPase about 20 per cent and transcription processes 5–10 per cent of the total ATP. The share of the Ca2+‐dependent reactions was notably high at 25 per cent in comparison with Ehrlich mouse ascites tumour cells, reticulocytes or hepatocytes. ATP consumption by DNA synthesis was assessed at 5–10 per cent. Only less than 10 per cent of the consumption of ATP produced oxidatively remained for other cellular reactions. The degree of coupling of K 562 cells was high in comparison with that of other eukary

ISSN:0263-6484    

DOI:10.1002/cbf.290100110

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

ISSN:0263-6484    

DOI:10.1002/cbf.290100113

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY