摘要:

AbstractThe possible relevance of changes in extracellular and/or intracellular pH to the insulinotropic action ofL‐arginine andL‐homoarginine was investigated in rat pancreatic islets. A rise in extracellular pH from 7·0 to 7·4 and 7·8 augmented the secretory response to these cationic amino acids whilst failing to affect the uptake ofL‐arginine by islet cells and whilst decreasing the release of insulin evoked byD‐glucose. Under these conditions, a qualified dissociation was also observed between secretory data and45Ca net uptake. Moreover, at high extracellular pH, the homoarginine‐induced increase in86Rb outflow from prelabelled islets rapidly faded out, despite sustained stimulation of insulin release. The cationic amino acids failed to affect the intracellular pH of islet cells, whether in the absence or presence ofD‐glucose and whether at normal or abnormal extracellular pH. These findings argue against the view that the secretory response toL‐arginine would be related to either a change in cytosolic pH or the accumulation of this positively charged amino acid in the β‐cell. Nevertheless, they suggest that the yet unidentified target forL‐arginine and its non‐metabolized analogue in islet cells displays pH‐dependency with optimal resp

ISSN:0263-6484    

DOI:10.1002/cbf.290090102

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractEfflux of Pi from rat hepatocytes suspended in phosphate free‐medium was studied by chemical assay of released Pi and by monitoring the loss in radioactivity of cells pre‐labelled with [32P]‐Pi. The release follows first‐order kinetics fairly closely with a rate constant of 7 × 10−3min−1approximately. Insulin at a concentration of 10−8Mhad no effect on the rate of Pi release and it is concluded therefore, that the insulin‐stimulated accumulation of Pi described in the literature is the result of hormone action on Pi uptake by liver rather tha

ISSN:0263-6484    

DOI:10.1002/cbf.290090103

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe flux through branched‐chain α‐ketoacid dehydrogenase and the activity of the branched‐chain α‐ketoacid dehydrogenase complex were measured in hepatocytes isolated from fed, starved and alloxan diabetic rats. The highest rate of branched‐chain α‐ketoacid oxidation was found in hepatocytes isolated from starved rats, slightly lower in those from fed rats, and significantly lower in diabetic hepatocytes. The amount of the active form of branched‐chain α‐ketoacid dehydrogenase was only slightly diminished in diabetic hepatocytes, whereas the flux through the dehydrogenase was inversely correlated with the rate of endogeneous ketogenesis. The same was observed in hepatocytes isolated from starved rats when branched‐chain α‐ketoacid oxidation was measured in the presence of added oleate. In both cases the diminshed flux through the dehydrogenase, restored by a short preincubation of hepatocytes with insulin, was parallelled by a decrease of fatty acid‐derived ketogenesis. The significance of these findings is discussed in relation to the role of insulin in branched‐chain α‐ketoacid oxid

ISSN:0263-6484    

DOI:10.1002/cbf.290090104

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractUsing turbidometry, electron microscopy and immunofluorescent microscopy experiments we studied the effect of captan, a widely used pesticide on mammalian microtubules and microfilaments. Turbidometry at 350 nm showed a dose‐dependent inhibition of tubulin assembly incubated with captan. The pesticide, given at equimolar concentration with tubulin (30 μM), caused the total inhibition of microtubule formation, while at lower concentrations (5–20 μM) the inhibition of tubulin polymerization was less extensive. At the same concentration range (5–30 μM), captan also promoted the disassembly of performed microtubules. The results of thein vitroeffects of captan with microtubules were confirmed in parallel by electron microscopic studies.In vivo, captan caused also depolymerization of microtubules in cultured mouse fibroblasts as shown by indirect immunofluorescent staining of tubulin. The extent of microtubules disassembly was concentration‐ and time‐dependent. While incubation of the cells with 10 μMcaptan for 3 h disturbs totally the microtubular structures, incubation with 5 μMcaptan needs 12 h for the same effect. Recovery of microtubules was observed, when preincubated cells were extensively washed. No interaction of this drug with equimolar concentration of G‐ or F‐actin could be observedin vitro, as shown by polymerization experiments. In line with this, the fluorescent actin pattern in mouse fibroblasts incubated with 10 mMcaptan for up to 12 h did not seem to be altered. From these results it is concluded that captan interacts in equimolar concentrations with tubulin affecting the assembly and disassembly of microtubulesin vitroand in cultures

ISSN:0263-6484    

DOI:10.1002/cbf.290090105

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe stimuli, sn‐1, 2‐dioctanoylglycerol; (DG8) the calcium specific inophore, ionomycin, and the chemotactic peptide formylmethionyl‐leucyl‐phenylalanine (FMLP) can interact with normal human neutrophils and activate their superoxide/hydrogen peroxide generating NADPH‐oxidase. In response to the peptide as well as DG8, the neutrophils produced both superoxide (O2−) and hydrogen peroxide (H2O2). Since interaction between the cells and ionomycin was not associated with any notable superoxide production and hydrogen peroxide was induced only in the presence of azide, a potent inhibitor of the hydrogen peroxide‐consuming enzymes catalase and myeloperoxidase, we conclude that this stimulus can generate oxygen metabolites intracellularly. Since the DG8‐induced production of hydrogen peroxide was increased in the presence of azide, whereas the FMLP‐induced response was largely unaffected, we concluded that the three stimuli differ in their capacity to generate oxygen metabolites intracellularly.The use of sn‐1,2‐didecanoylgylycerol (DG10) as stimulating agent did not result in any detectable activation of the NADPH‐oxidase. However, preincubation caused an increased (primed) response during stimulation with the chemotactic peptide FMLP. The response of primed neutrophils to FMLP proceeds with a time‐course different from that seen in normal cells. From the results presented on FMLP‐induced activity in the presence of azide, we conclude that FMLP causes normal cells to produce oxygen radicals which are released from the cells. However, the primed cells are also capable of generating oxygen metabolites that are retained inside the cells. In fact, measurement of the intracellularly generated metabolites discloses this to be the predo

ISSN:0263-6484    

DOI:10.1002/cbf.290090106

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractStudies were conducted to determine the relationship between the pretherapy characteristics of leukemia cells and their behaviour during culturein vitro. Leukemia cells which proliferated wellin vitroalso proliferated wellin vivo. Cells which manifested myeloid or monocytic differentiationin vivotended to manifest differentiation along these linesin vitro. Cells which manifested high levels of expression of c‐fms, c‐fes, or triose phosphate isomerase prior to culture were likely to differentiatein vitro, with high levels of c‐fes expression being related to myeloid maturation. These observations suggest that differentiation at the molecular level prior to culture is a requisite for leukemia cell differentiationin vitro. The same may be true for differentiationin vivounder the influence of exogenously administered agents such as cytotoxic chemotherapy or recombinant growth fa

ISSN:0263-6484    

DOI:10.1002/cbf.290090107

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe relative contribution of each anomer of D‐glucose to the overall phosphorylation rate of the hexose tested at anomeric equilibrium was examined in rat liver postmicrosomal supernatants under conditions aimed at characterizing the activity of glucokinase, with negligible interference of either hexokinase,N‐acetyl‐D‐glucosamine kinase or glucose‐6‐phosphatase (acting as a phosphotransferase). Both at 10° and 30°C, the relative contribution of each anomer was unaffected by the concentration ofD‐glucose. At both temperatures, the α/β ratio for the contribution of each anomer was slightly, but significantly, lower than the α/β ratio of anomer concentrations. These findings, which are consistent with the anomeric specificity of glucokinase in terms of affinity, cooperativity and maximal velocity, reveal that the preferred α‐anomeric substrate for both glycogen synthesis and glycolysis is generated by glucokinase at a lower rate than is

ISSN:0263-6484    

DOI:10.1002/cbf.290090108

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe protease activity of cultured normal human skin fibroblasts was studied using the synthetic fluorigenic peptides, the modified protein 4‐methylumbelliferyl‐casein, the thiol inhibitors and the affinity for concanavalin A‐Sepharose. The majority of the activity toN‐benzyloxycarbonyl‐L‐phenylalanyl‐L‐arginyl‐7‐amido‐4‐methyl‐coumarin andN‐a‐benzyloxycarbonyl‐L‐arginyl‐arginyl‐7‐amido‐4‐methylcoumarin had a pH optimum of 6·0, and was thiol‐dependent and inhibited by leupeptin and antipain. The activity towardN‐benzyloxycarbonyl‐L‐phenylalanyl‐L‐arginyl‐7‐amido‐4‐methylcoumarin represents both cathepsin B and cathepsin L, whereas the activity towards 4‐methylumbelliferyl‐casein represent only cathepsin L. Cathepsin H could not be detected when assayed with L‐arginine‐7‐amido‐4‐methylcoumarin substrate. Cathepsin D was present in comparatively small amounts when assayed with 4‐methylumbelliferyl‐casein. Activity towards 4‐methylumbelliferyl‐casein had pH optima at 3 and 6 and was stimulated by dithiothreitol. A proportion of the activity at pH 6·0 was not dependent on thiols and not inhibited by leupeptin, and had the general characteristics of a carboxyl proteinase. Over 70 per cent of the activity was in the lysosomal fraction and showed structure‐linked latency. All the detectable protein emerged from the immobilized concanavalin A column and the fractions eluted by α‐methyl‐D‐mannoside were significantly hydrolysed the synthetic peptides. Only that fraction which bound to concanavalin A was active towards 4‐methylumbelliferyl‐casein. Cathepsin B had no affinity for concanavalin A‐Sepharose due to the absence o

ISSN:0263-6484    

DOI:10.1002/cbf.290090109

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

摘要:

AbstractThe synthesis, distribution and types of collagen produced by somatic testicular cells in culture was studied. To investigate whether changes in collagen synthesis correlate with the age of the animal, cultures derived from immature and pubertal rats were established. Immature rats synthesize 40 per cent more collagen than pubertal rats. Both groups of animals synthesize procollagen types I and III. Pro‐collagen type I is present in the culture medium as well as in the cell fraction, while type III is only detected in the culture medium. In the transition from immature to pubertal rat, the ratio of procollagen type III to procollagen type I diminishes from 5·7 to 1·7. These results indicate that the synthesis, distribution and molecular characteristics of interstitial collagens changes with the age of the animal. Since, the content of other extracellular matrix components such as proteoglycans and collagen type IV also varies with age, we postulate that the composition of the extracellular matrix in the testes is not constant but changes with sexual developm

ISSN:0263-6484    

DOI:10.1002/cbf.290090110

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY

ISSN:0263-6484    

DOI:10.1002/cbf.290090112

出版商:John Wiley&Sons, Ltd.    

年代:1991

数据来源: WILEY