Biochimica et biophysica acta
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Biochim. Biophys. Acta · Jun 1997
Regulation of protein turnover by glutamine in heat-shocked skeletal myotubes.
Skeletal muscle accounts for approximately one-half of the protein pool in the whole body. Regulation of protein turnover in skeletal muscle is critical to protein homeostasis in the whole body. Glutamine has been suggested to exert an anabolic effect on protein turnover in skeletal muscle. ⋯ In normal-cultured myotubes, when glutamine concentration increased from 0 to 15 mM, the half-life of long-lived proteins increased 35% (P < 0.001) while in stressed myotubes, it increased 27% (P < 0.001). We also found that glutamine can significantly (P < 0.001) increase the levels of heat-shock protein 70 (HSP70) in stressed myotubes, indicating that HSP 70 may participate in the mechanism underlying the effect of glutamine on protein turnover. We conclude that in cultured skeletal myotubes the stimulatory effect of glutamine on the rate of protein synthesis is condition-dependent, and that the inhibitory effect of glutamine on the rate of protein degradation occurs only on long-lived proteins.
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Biochim. Biophys. Acta · Oct 1995
In vivo 19F-NMR spectroscopic study of halothane uptake in rabbit brain.
Uptake of a fluorinated anesthetic, halothane, in rabbit brain and blood was studied using 19F-NMR spectroscopic techniques. Localized one-dimensional chemical shift imaging and non-localized one-pulse sequence were used to measure brain uptake kinetics in vivo. Halothane signal was found predominantly in the cerebral cortex. ⋯ Uptake in the arterial blood was also biexponential. However, equilibration of halothane in the brain considerably lagged behind that in arterial blood. This delay was ascribed to a 'restricted diffusion' of the anesthetic molecule into brain tissue.
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Biochim. Biophys. Acta · Aug 1994
Comparative StudyAnesthetic alteration of ryanodine binding by cardiac calcium release channels.
Differential cardiac contractile depression by volatile anesthetics is well documented, and evidence points to differing actions on the myocardial sarcoplasmic reticulum (SR). Since the Ca(2+)-release channel (CaRC) of the SR binds ryanodine with high-affinity when opened by micromolar Ca2+ concentrations, ryanodine binding to cardiac SR membrane vesicles was employed as an assay of anesthetic modulation of CaRC activity. Canine ventricle was homogenized, centrifuged preparatively and then differentially on a sucrose gradient. ⋯ With submaximal activation by 5 microM Ca2+, 1.5% and 0.75% halothane enhanced binding of 10-80 microM ryanodine, while 2.5% isoflurane and 3.5% enflurane did not. A plot of bound/free vs. bound ryanodine suggests that halothane causes a dose-dependent increase in ryanodine binding to a high-affinity site, while isoflurane has no such action. In intact myocardium, this effect will decrease Ca2+ retention in the SR so that less Ca2+ will be available to activate contractions, consistent with halothane's depressant action.
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Biochim. Biophys. Acta · Oct 1991
Spin traps inhibit formation of hydrogen peroxide via the dismutation of superoxide: implications for spin trapping the hydroxyl free radical.
To enhance the sensitivity of EPR spin trapping for radicals of limited reactivity, high concentrations (10-100 mM) of spin traps are routinely used. We noted that in contrast to results with other hydroxyl radical detection systems, superoxide dismutase (SOD) often increased the amount of hydroxyl radical-derived spin adducts of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) produced by the reaction of hypoxanthine, xanthine oxidase and iron. One possible explanation for these results is that high DMPO concentrations (approximately 100 mM) inhibit dismutation of superoxide (O2.-) to hydrogen peroxide (H2O2). ⋯ However, alpha-phenyl-N-tert-butylnitrone (PBN, 10 mM), 3,3,5,5 tetramethyl-1-pyrroline N-oxide (M4PO, 100 mM), alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN, 100 mM) had no effect. These data suggest that in experimental systems in which the rate of O2.- generation is low, formation of H2O2 and thus other H2O2-derived species (e.g., OH) may be inhibited by commonly used concentrations of some spin traps. Thus, under some experimental conditions spin traps may potentially prevent production of the very free radical species they are being used to detect.
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Biochim. Biophys. Acta · Jul 1991
Further studies on the purine phosphoribosyltransferase 'burst' velocity reaction.
In the assays used to determinate the adenine and hypoxanthine-guanine phosphoribosyltransferases activities from Artemia cysts two phases of velocity are observed in the synthesis of AMP, IMP and GMP: one initial burst and a second, slower, steady-state velocity. Both reaction velocities are divalent cation-dependent and temperature-resistant, as they are detectable at temperatures from 0 to 100 degrees C. ⋯ The 'burst' phase is not detected when the reaction is ended by the addition of EDTA. These data support that the initial velocities of these enzymatic reactions may be due to the accumulation of products formed by the overall reaction, developed subsequent to the controlled reaction period, being the 'burst' a result from the relative resistance of these enzymes to the agents that are often used to stop the reaction, such as heat or butanol.