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At least 793 records · Page 44Linked to original sources

PubMed1985

Effects of cyclic GMP-agonists on cyclosporin-induced suppression of human lymphokine production.

Cyclosporin (Cs) inhibits the elaboration of the lymphokine leukocyte migration inhibitory factor (LIF) from human blood mononuclear cells (MNC) stimulated with recall antigen. This inhibition was counteracted by 3 X 10(-5) M dibutyryl-cyclic GMP and 8-bromo-cyclic GMP and by the cyclic GMP-agonists, sodium nitroprusside (NaNPr), ascorbic acid (As A), sodium azide (NaN3) and carbacholine. Using 5 X 10(-5) M NaNPr, 1 X 10(-3) M NaN3, or 3 X 10(-3) M As A, 25-50-, 4-8- and 2-3-fold elevations of MNC and T-lymphocyte cyclic GMP-levels were obtained independently of the presence of Cs. NaNPr was the most potent of these three cyclic GMP-agonists in counteracting the effect of Cs. The results indicate that intracellular cyclic GMP is a major factor involved in the reversal of Cs-induced inhibition of LIF-production. None of the cyclic GMP-analogues or -agonists by themselves possessed Interleukin 1-like activity, measured by their ability to induce LIF-production by macrophage-depleted T-lymphocytes challenged by recall antigen.

Adult↗

PubMed1991

Aluminum salts stimulate luminol-enhanced chemiluminescence production by human neutrophils.

Aluminum intoxication is currently thought to play a major role in the development of Alzheimer's disease and in certain pathologic manifestations seen during long-term hemodialysis and aging. The hypothesis that aluminum toxicity is mediated via an increased free radical production was tested by studying the effects of two aluminum and five other metallic compounds on the production of luminol-enhanced chemiluminescence (LECL) by human neutrophils. AlCl3, Al2(SO4)3 and FeCl3 were found to stimulate LECL production by human neutrophils whereas FeCl2, CuCl, CuCl2, AuCl3 were inactive. Metal chelators such as Desferal, EDTA and DETAPA suppressed aluminum-induced stimulation and depressed cell-dependent LECL below basal levels. Sodium azide and Cytochalasin B greatly depressed both basal and aluminum-induced stimulation of LECL production, suggesting that, in this system, most of this stimulation was due to myeloperoxidase. These results suggest that high tissue aluminum concentrations may induce cell-tissue lesions by stimulating local production or release of mediators of tissue damage.

Alum Compounds↗

PubMed1991

Effects of oxidants on protein breakdown in skeletal muscle.

Oxidants have been found to increase protein breakdown in erythroid cells. In skeletal muscle, phenylhydrazine decreased by 24-28% rates of protein degradation. Both H2O2 (5 mM) and glucose oxidase (0.2 U/ml) decreased by 82-88% rates of proteolysis only in skeletal muscles pretreated with sodium azide (0.25 mM) to inactivate endogenous catalase. Thus, the effect of various oxidants on protein breakdown may differ depending on the cell or tissue type.

Animals↗

PubMedDate not supplied

[Effect of inhibitors on the viability and protein and nucleic acid synthesis of Escherichia coli].

The object of this work was to study how the synthesis of protein, RNA and DNA in Escherichia coli M17 and its viability were influenced by chloramphenicol (50 and 300 micrograms/ml) an inhibitor of protein biosynthesis, and sodium azide (200 and 2000 microM) and aminazine (50 micrograms/ml), inhibitors of respiration. The exposed were inhibitors with the bacteria for 60 min at room temperature and for 1-4 months at -10 degrees C. The inhibition of the E. coli viability by chloramphenicol was shown to be reversible. The respiration inhibitors stabilized its viability upon storage at -10 degrees C for one month. The inhibitors were found to produce a different effect on the synthesis of RNA and protein in E. coli. The rates of DNA synthesis hardly changed. No correlation was established between changes in the synthesis of protein and nucleic acids by E. coli after the action of the inhibitors and its viability.

Azides↗

PubMed1986

BAY-K-8644-stimulated cyclic GMP synthesis in mouse pituitary tumor cells.

The 1,4-dihydropyridine BAY-K-8644 [methyl-1,4-dihydro-2, 6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyridine-5-carboxylate] acts as both a calcium channel agonist and antagonist by stimulating or inhibiting inward calcium current. In AtT-20 mouse pituitary tumor cells, BAY-K-8644 both stimulates and blocks adrenocorticotropin (ACTH) secretion. Because in several cell systems the cytoplasmic enzyme guanylate cyclase is activated, presumably by calcium entry, the effect of BAY-K-8644 on cyclic GMP (cGMP) synthesis in AtT-20 cells was assessed. BAY-K-8644 increased cGMP accumulation in a time-dependent manner. The concentrations of BAY-K-8644, however, required to increase cGMP formation were not associated with its stimulatory effects on secretion but rather with its ability to antagonize basal and (-)-isoproterenol-induced ACTH secretion. The inhibitory effect of BAY-K-8644 on ACTH secretion was not mimicked by 8-Br-cGMP. The cGMP response to BAY-K-8644 was not mimicked by the cationophore, A-23187, or depolarizing concentrations of K+. Other calcium channel antagonists such as nifedipine or verapamil had markedly smaller effects on cGMP formation compared to BAY-K-8644. Sodium nitroprusside and sodium azide both increased cGMP synthesis in AtT-20 cells and both inhibited, to a lesser extent than BAY-K-8644, both basal- and (-)-isoproterenol-stimulated ACTH release. The data suggest that BAY-K-8644 stimulates cGMP synthesis by binding to sites less accessible or poorly activated by other dihydropyridines, and that stimulation of guanylate cyclase is independent of inward calcium current.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1988

Effect of cellular inhibitors on the infection of various susceptible cells with vesicular stomatitis virus.

The effect of some cellular function inhibitors on adsorption and successive events of penetration of vesicular stomatitis virus to phylogenetically unrelated permissive cells was investigated. Treatment of HeLa, CER, EPC and Aedes albopictus cells with colcemide and cytochalasin D which affect cytoskeleton organization indicated that microfilaments but not microtubules were involved in the early events of VSV infection. Inhibitors of oxidative phosphorylation such as dinitrophenol and sodium azide, and the glycolysis inhibitor 2-deoxy-D-glucose, did not allow multiplication of prebound virions, demonstrating that VSV replication is largely energy dependent in either host cells examined.

Adsorption↗

PubMed1986

Mechanism of phagocytosis of mycobacteria by Schwann cells and their comparison with macrophages.

Factors influencing the phagocytosis of mycobacteria by 33B rat Schwannoma cells and rat peritoneal macrophages were studied. Uptake of 14C-acetate-labeled Mycobacterium w by these cells was used to set up a radiometric phagocytosis assay. Incubation at 4 degrees C and treatment with sodium azide (0.2% to 1%), colchicine (10(-7) to 10(-3) M), cytochalasin B (0.2 micrograms/ml to 25 micrograms/ml), and dibutyryl cyclic AMP (10(-7) to 10(-3) M) inhibited the phagocytosis by both cell types in a similar manner. These experiments demonstrate similarities in the mechanism of phagocytosis of mycobacteria by Schwann cells and macrophages.

Animals↗

PubMed1988

Muscarinic receptors on rat lymphocytes; internalization of receptor-ligand complex.

In the light of the data presented, the previously described explanation of the unusual shape of the kinetic curve of the muscarinic antagonist 3H-QNB binding to rat lymphocytes, with apparent maximum of bound radioactivity after 5 min of incubation, followed by decrease of specific binding, is not satisfactory. The kinetics of this binding carried out at 4 degrees C, 20 degrees C and 37 degrees C, or in the presence of the metabolic poison sodium azide, suggests involvement of an energy-consuming mechanism in this process. The surface receptors, sensitive to bacterial protease degradation before 3H-QNB binding, become somehow resistant to this protease action after 5 min of incubation of the cells with 3H-QNB. A possible explanation for this phenomenon, based on internalization in cell endosomes, is presented.

Animals↗

PubMed1982

Localization of glycerophosphate acyltransferase in Escherichia coli.

sn-Glycero-3-phosphate acyltransferase (EC 2.3.1.15) the first enzyme involved in phospholipid biosynthesis, is known to be associated with the cytoplasmic membrane of Escherichia coli. The localization of this enzyme in the transverse plane of the membrane was investigated by proteolysis of intact and lysed spheroplasts and by inhibition of glycerol 3-phosphate transport into intact cells in the presence of azide. Glycerophosphate acyltransferase was found to be resistant to proteolysis by trypsin in intact spheroplasts, whereas its enzymatic activity could be destroyed completely by trypsin in lysed spheroplasts. These results are in line with a localization of the acyltransferase at the inner aspect of the cytoplasmic membrane. Sodium azide was shown to have no inhibitory effect on glycerophosphate acyltransferase activity. Lack of incorporation of glycero phosphate into the phospholipids of glycerol phosphate transport-negative cells and inhibition of this incorporation in wild-type and glycerol 3-phosphate transport-constitutive cells by azide support a cytoplasmic-oriented localization of the glycerophosphate acyltransferase.

Acyltransferases↗

PubMedDate not supplied

Pholasin chemiluminescence detects mostly superoxide anion released from activated human neutrophils.

The bioluminescent oxygen metabolite indicator protein pholasin was characterized with respect to the type and location of reactive oxygen metabolites detected in suspensions of stimulated human neutrophils. Whereas pholasin detected reactive oxygen metabolites from neutrophil suspensions stimulated with soluble agents, particulate stimulants were apparently not effective triggering agents for pholasin-dependent neutrophil chemiluminescence. Neutrophils stimulated with fMet-Leu-Phe (1 to 100 nmol/l) showed maximum pholasin-dependent chemiluminescence 45 to 60 s after stimulation. The time of maximum chemiluminescence was virtually independent of fMet-Leu-Phe concentration. In contrast, the time to reach maximum light emission increased from 60 s with 100 nmol/l phorbol ester to 295 s with 1 nmol/l phorbol ester. Significant inhibition of stimulated chemiluminescence was caused by both superoxide dismutase (20 micrograms/ml, 80% inhibition) and reduction of the oxygen concentration in the incubation medium to less than 0.5 mumol/l (95% inhibition). In contrast, the myeloperoxidase inhibitor sodium azide (0.1 mmol/l) afforded only 50% inhibition of the pholasin-dependent neutrophil chemiluminescence. Our results show that pholasin detects superoxide radicals released from cells stimulated by soluble stimulants but not intracellular oxidative activity elicited by particulate stimulants.

Azides↗

PubMed1996

Control of spoT-dependent ppGpp synthesis and degradation in Escherichia coli.

Escherichia coli has two ppGpp synthetases, PSI and PSII, encoded by the relA and spoT genes. The spoT gene also encodes a ppGpp hydrolase. During exponential growth and under various starvation conditions, the level of ppGpp depends on the balance of ppGpp synthetic and degradative activities of spoT gene products. To find out how these two activities respond to different physiological conditions and to learn about the signals involved in these responses, rates of ppGpp synthesis and degradation were determined in an E. coli B/r delta relA strain during: (1) multiple amino acid deprivation after a nutritional shift-down from glucose amino acids to glucose minimal medium; (2) carbon source starvation after a "glucose runout"; (3) energy starvation by treatment with sodium azide. To each of these conditions, bacteria responded with a similar gradual accumulation of ppGpp, occurring over a period of 20 to 40 minutes, from the basal level of 4 and 24 pmol/OD460 in glucose amino acids and glucose minimal medium, respectively, to about 100 pmol ppGpp/OD460 unit of culture mass. After multiple amino acid deprivation and during azide treatment, the rate of ppGpp synthesis increased and the rate of ppGpp degradation decreased, but in different proportions by the two kinds of treatment. After glucose runout, both ppGpp synthesis and degradation immediately decreased, but the rate of degradation was reduced more, which caused the accumulation of ppGpp despite its reduced synthesis. ppGpp synthesis required continuous protein synthesis, but ppGpp hydrolysis and its control did not: the rate of ppGpp degradation could be instantly up or down-regulated in response to changes in exogenous amino acid or glucose levels in the absence of protein synthesis. The results suggest that PSII is unstable with an average functional lifetime of 40 seconds or less, and that its activity is generated during or shortly after spoT mRNA translation in response to the availability of amino acids. This regulation is responsible for the growth medium-dependent changes in basal levels of ppGpp. ppGpp hydrolysis is controlled, i.e. inhibited, mainly during conditions of physiological stress, such as multiple amino acid deprivation or energy deprivation. This inhibition can be correlated with an inferred accumulation of uncharged tRNA. Since previous reports have indicated that uncharged tRNA inhibits purified SpoT hydrolase in vitro, it is proposed that ppGpp hydrolase activity is, indeed, controlled by the concentration of uncharged tRNA in the cell. Finally, it was found that neither relC, transcriptional regulation of spoT, nor different translation starts of spoT mRNA are directly involved in the environmental control of SpoT hydrolase and PSII activities.

Amino Acids↗

PubMed1985

Use of mitochondrial inhibitors to differentiate kinetic properties of the ATP-dependent Ca2+ uptake system in synaptic membranes.

Synaptosomal membranes accumulate 3-6 times more Ca2+ in the presence of ATP (50-1000 microM) than basal Ca2+ accumulation (-ATP). The location of this Ca2+ accumulation appears to reside on the cytosolic face of the synaptosome since lysed synaptosomes accumulate 4-times more Ca2+ than intact synaptosomes. The inclusion of mitochondrial inhibitors, oligomycin (0.7 micrograms/ml), sodium azide (100 microM) and dinitrophenol (100 microM) differentiate mitochondrial from nonmitochondrial Ca2+ accumulation under conditions that are [Ca2+]- and ATP-dependent. In the presence of low concentrations of ATP (less than 150 microM) and Ca2+ free (2.5 or 6.8 microM), Ca2+ accumulation occurs as one process in both lysed synaptosomal membranes and purified synaptic plasma membranes in the presence and/or absence of MI. When ATP levels are increased (greater than 200 microM), Ca2+ accumulation process remains independent of the presence of mitochondrial inhibitors when Ca2+ free = 2.5 microM. When Ca2+ free is increased to 6.8 microM, mitochondrial inhibitors differentiate mitochondrial from nonmitochondrial accumulation. These studies suggest that optimal conditions for the measurement of Ca2+ accumulating mechanisms in synaptosomal membranes depend on both [Ca2+] and ATP. Use of these assay conditions provide evidence that ATP-dependent Ca2+ uptake may be a viable mechanism for the regulation of synaptosomal Ca2+ levels.

Adenosine Triphosphate↗

PubMed1983

Identification and characterization of a plasma membrane phosphoprotein which is present in Chinese hamster lung cells resistant to adriamycin.

Studies have been carried out to analyze the phosphoprotein composition of plasma membranes from Chinese hamster lung cells resistant to the action of adriamycin. Gel electrophoretic analysis of [32Pi]-labeled proteins revealed that plasma membranes from resistant cells contain a phosphoprotein of 180,000 molecular weight (P180) which is not detected in drug sensitive cells. Protein P180 can also be identified after phosphorylation of resistant plasma membranes in an in vitro protein kinase system. Pulse-chase experiments indicated that the P180 was metabolically active and underwent cycles of phosphorylation and dephosphorylation in the cell. Additional studies showed that, in the presence of N-ethylmaleimide (NEM), there was a major increase in the uptake of adriamycin in resistant cells. A similar effect was observed with KCN but not with sodium azide. When resistant cells were grown in the presence of [32Pi] and then incubated in the presence of NEM, there was a considerable increase in the phosphorylation of P180. In contrast, many other plasma membrane proteins were dephosphorylated under these incubation conditions. The results suggest the possibility that, as P180 was hyperphosphorylated, the protein was inactivated and this contributed to the ability of resistant cells to accumulate adriamycin.

Animals↗

PubMed1988

Doxorubicin cellular pharmacokinetics and DNA breakage in a multi-drug resistant B16 melanoma cell line.

Mechanisms of anthracycline resistance have been investigated in a B16 murine melanoma cell subline selected by continuous in vitro exposure to increasing concentrations of doxorubicin (DX). Altered drug pharmacokinetics were observed in resistant B16 cells as compared to the sensitive counterpart. In fact, cellular DX uptake - as determined by a fluorescence method - was lower in resistant than in sensitive cells. Furthermore, drug efflux rate was shown to be higher in resistant than in sensitive cells; treatment of cells with the metabolic inhibitor sodium azide decreased drug efflux rate in resistant but not in sensitive cells, suggesting the presence of an energy-dependent drug extrusion mechanism in the resistant B16 cells. However, since drug-induced cell killing did not correlate with cellular DX contents in sensitive and resistant cells, drug resistance of B16 subline could not be completely explained by the observed differences in drug pharmacokinetics. Since drug-induced DNA breaks have been related to drug cytotoxicity, DNA cleavage was also measured by alkaline elution methods. The number of DNA breaks produced by DX was decreased in resistant cells as compared to sensitive cells at the same cellular drug accumulation. The results are consistent with the view that anthracycline resistance may be multifactorial and probably arises following multiple biochemical changes.

Animals↗

PubMed1989

Phorbol myristate acetate inhibits acidification by turtle urinary bladder.

The effects of phorbol myristate acetate (PMA) on acid secretion by the turtle urinary bladder were examined to evaluate the importance of protein phosphorylation in modulating the distal acidification system. In HCO3-free PO4 buffer 0.2 mM mucosal PMA inhibited reverse short-circuit current (RSCC) by 42%. The inhibition of RSCC was dose dependent, and RSCC approached zero at high concentrations of PMA. PMA also inhibited acid secretion measured titrimetrically but had no effect on RSCC from bladders in which proton secretion was selectively inhibited by an adverse pH gradient or serosal 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid. The inhibition by PMA was duplicated by 1-oleoyl-2-acetyl-rac-glycerol, but not by an inactive phorbol ester. The PMA inhibition was much more potent with mucosal compared with serosal application. The PMA inhibition caused a significant 0.15 pH unit reduction of carbonic anhydrase (CA) cell cytoplasmic pH and a change in the CA cell morphology. Unlike the inhibition of proton transport induced by acetazolamide, the PMA inhibition was neither reversed nor prevented by sodium azide. We conclude that PMA decreases basal acid secretion and blocks the stimulatory effects of CO2 by an azide-insensitive mechanism distinct from that of acetazolamide. In view of recent findings that PMA stimulates HCO3 secretion by the turtle bladder, these results suggest that kinase C-mediated protein phosphorylation may be a central event in the transition from the secretion of acid to the secretion of base.

1-Methyl-3-isobutylxanthine↗

PubMedDate not supplied

Effects of oxygen and glucose deprivation on vasoactivity in isolated bovine middle cerebral arteries.

The effects of oxygen and glucose deprivation on vasoactivity were investigated using helical strips of bovine middle cerebral artery. Hypoxia, created by reducing the PO2 of the bath, or oxidative inhibition with 2,4 dinitrophenol (DNP) or sodium azide, significantly reduced contractions induced by serotonin. Normal tonic contractions induced with fresh and aged whole blood, or 5-HT became phasic and quickly relaxed to baseline in a hypoxic environment. Glucose elimination from the Krebs medium, or the inhibition of the glycolytic pathway with iodoacetic acid (IAA), did not significantly reduce serotonin-induced contractions. However, contractions were inhibited more with the combination of oxygen and glucose deprivation, or DNP + IAA, than with oxygen deprivation alone. Efforts to produce rigor in this preparation by oxygen/substrate reduction or metabolic inhibition were unsuccessful. Tonic contractions induced by 70 mM potassium became phasic as the Ca++ concentration was reduced. Contractions resulting from the readdition of Ca++ to arteries exposed to calcium-free high potassium solution were significantly reduced in the presence of oxidative and/or glycolytic inhibitors. The uptake of 45Ca++, as measured by the lanthanum technique, decreased as the bath PO2 was reduced in both serotonin stimulated and unstimulated arteries. Glucose deprivation alone did not affect 45Ca++ uptake. This study suggests that hypoxia has a direct inhibitory affect on cerebral vasoactivity mediated by reductions in sarcoplasmic Ca++ uptake.

2,4-Dinitrophenol↗

PubMed1988

Toxic effects produced or mediated by human eosinophil granule components on Trypanosoma cruzi.

The eosinophil granule major basic protein, the eosinophil cationic protein, and the eosinophil-derived neurotoxin were found to be lytic for Trypanosoma cruzi trypomastigotes from blood, cell cultures, or insect vectors and for cultured amastigotes. The toxic effects of the major basic and cationic proteins were inhibited by the polyanions heparin and dextran sulfate, in keeping with the cationic nature of these proteins, or by heat denaturation, suggesting that molecular conformation was also relevant. The lytic activity of the neurotoxin was not inhibited by heating at 56 degrees C for 4 hr, establishing an additional difference with the eosinophil cationic protein. Heparin had only a slight inhibitory effect on the toxicity of the neurotoxin, and dextran sulfate was inactive even at 25 mg/ml. Although both the eosinophil cationic protein and the neurotoxin possess ribonuclease activity, only the toxicity of the latter was abolished by the ribonuclease inhibitor RNasin (Promega, Madison, Wisconsin) or by a competitive substrate, yeast ribonucleic acid. Eosinophil peroxidase significantly increased the extent of trypomastigote or amastigote killing by hydrogen peroxide in the presence of iodide. This effect was abrogated by sodium azide, bovine serum albumin, or gelatin, known inhibitors of the eosinophil peroxidase + halide + hydrogen peroxide system. These results suggest that the destruction of T. cruzi trypomastigotes and amastigotes by eosinophils may result from toxic mechanisms involving several granule proteins.

Animals↗

PubMedDate not supplied

Oxidation of propylthiouracil to reactive metabolites by activated neutrophils. Implications for agranulocytosis.

Propylthiouracil (PTU) is associated with idiosyncratic agranulocytosis that may be due to reactive metabolites generated from oxidative metabolism by neutrophils. Therefore, the metabolism of PTU was investigated in activated neutrophils. Three oxidized metabolites were observed on HPLC: PTU-disulfide, propyluracil-2-sulfinate, and propyluracil-2-sulfonate (PTU-SO3-). No metabolism was detected in cells that had not been activated. Metabolism was inhibited by sodium azide and by catalase. The same products were produced by myeloperoxidase (MPO) in an MPO/H2O2/Cl- system. PTU inhibited its own metabolism; however, complete conversion to PTU-SO3- could be achieved with optimal PTU concentrations. MPO/H2O2 without Cl- produced only slight metabolism. The PTU-sulfenyl chloride is a postulated intermediate. In the absence of chloride, oxidation might proceed through propyluracil-2-sulfenic acid. The sulfenyl chloride and PTU-SO3- are both chemically reactive with sulfhydryl compounds such as N-acetylcysteine. Such reactive metabolites, generated by activated neutrophils, may be involved in hypersensitivity reactions associated with PTU, such as agranulocytosis.

Agranulocytosis↗