摘要:

AbstractWe show how quantitative information about proton handling in human skeletal muscle in exercise and recovery can be obtained by31P MRS and illustrate this with data from metabolic disorders. Proton production, proton efflux and passive buffering can be distinguished by comparing changes in [phosphocreatine] and pH at the end of exercise and by calculating ATP turnover during ischaemic exercise and in the ‘natural experiment’ of myophosphorylase deficiency (McArdle's disease). We calculate the effective buffer capacity to be 20–30 mmol/L/pH unit (slykes), somewhat lower than published measurements madein vitrobut similar to other values obtainedin vivo. This analysis is applied to data from normal muscle and a variety of disease states to estimate proton efflux during recovery and ATP production during exercise: (i) proton efflux during recovery is pH‐dependent, reaching a 10 mmol/L/min at pH 6.2, and is increased in some cases of mitochondrial myopathy and in hypertension; (ii) glycogenolytic ATP production during exercise can reach 25 mmol/L/min in normal muscle and correlates approximately with [Pi] at the start of aerobic exercise and throughout ischaemic exercise; (iii) oxidative ATP production can reach 20–25 mmol/L/min and (as during recovery) correlates approximately

ISSN:0952-3480    

DOI:10.1002/nbm.1940060112

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractNMR spectroscopy, possibly, does not detect 100% of large molecules such as glycogen (mol. wt = 107–109). Using both NMR and chemical quantification methods, we have, therefore, determined the NMR visibility of cardiac glycogen (defined as the ratio of the NMR value to the chemical value, expressed as a percentage) in the isolated, perfused heart. Rats (n= 7) were pretreated for 60 min with 0.2mg/kg isoproterenol (s.c.) to deplete their endogenous myocardial glycogen stores (mainly12C). The hearts were then aerobically perfused (65 cm H2O, at 37 °C) in a double‐walled chamber (the annulus contained a standard), for 70 min with Krebs buffer plus 3.5 mM [13C]1‐glucose and 5 mM sodium acetate (natural abundance). From 70 to 175 min the sole substrate was natural abundance acetate (5 mM).13C NMR spectra for glycogen quantification were acquired in two different ways; by applying 896, 90° pulses at 0.33 s intervals with1H decoupling (‘fast’, practical spectra) and by applying 896, 90° pulses at 5 s intervals (‘slow’, impractical spectra). Hearts were then removed from the magnet, freeze‐clamped ( −196 °C) and analysed chemically. Cardiac glycogen, quantified from the ‘fast’ spectra (using conversion factors) and the ‘slow’ spectra was 16.8 ± 1.1 and 16.1 ± 1.8 (mean ± SEM) μmol glucosyl units/heart, respectively. After correction of the chemical value for the residual [12C]glycogen (determined from1H NMR spectra of the extracted glycogen after hydrolysis), the NMR‐visibilities were calculated to be 101 ± 6 and 109 ± 7%, for the ‘fast’ and ‘slow’ spectra, respectively. We conclude that, despite its size, cardiac glycogen is 100%

ISSN:0952-3480    

DOI:10.1002/nbm.1940060113

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractThe use of cerebral water as an internal intensity standard for the quantitation of spatially localized proton spectra of the human brain is investigated. The method is validated on standard samples ofN‐acetyl aspartate (NAA) and lactate, and possible sources of error are discussed. Using the STEAM pulse sequence, concentrations of choline, creatine and NAA in frontal lobe white matter are found to be 1.9±0.5, 10.6±1.3 and 16.6±2.3 μmol/g wet wt, respectively, in 10 normal volunteers. In the thalamus, the concentrations are 2.0±0.4, 11.6±2.0 and 17.2±1.3 μmol/g wet wt, respectively. Choline and creatine concentrations are in good agreement with conventional biochemical values: NAA concentrations are found to be three‐fold higher, suggesting overlap of the NAA signal with other compounds. Quantitation relative to tissue water is a convenient and rapid means of quantitating proton spectra of the

ISSN:0952-3480    

DOI:10.1002/nbm.1940060114

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractMR spectroscopy of cultured cells allows non‐invasive analyses of the metabolism of cells with specific phenotypes under defined conditions. This technique can be used to investigate the intracellular metabolism of cells or extended to critically evaluate phenomena observed byin vivoMRS. In this paper, a cell maintenance system is described which allows MR analyses with unparalleled spectral resolution, S/N and stability. This system consists of a 25 mm diameter hollow fiber bioreactor and a supporting circuit. The hollow fiber reactor was chosen because it yields a large filling factor which can be perfused through defined volumes. The fibers were 300 μm diameter microporous (0.2 μm) cellulose acetate/cellulose nitrate membranes with high porosity, which allow bulk convective flow throughout the extracapillary space. This flow (Starling flow) is necessary to disrupt steady‐state gradients in substrates and waste products. In many respects, the design of the supporting circuit is more important than the bioreactor itself, since it provides the reactor with the proper chemical and physical environment. Hence, this circuit can be applied to a variety of bioreactor configurations. The circuit consists of a hollow fiber oxygenator and a bleed‐and‐feed system housed in a temperature‐controlled cabinet. Culture of mammalian cells in this reactor yields31P spectra which have excellent spectral and temporal resolution. At confluence, endogenous31P line widths were typically<10 Hz (at 162 MHz) and well resolved spectra were obtai

ISSN:0952-3480    

DOI:10.1002/nbm.1940060115

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

摘要:

AbstractScyllo‐inositol has been identified in proton NMR spectra of mammalian brainin vitroandin vivo. In contrast tomyo‐inositol this isomer comprises six equivalent CH protons that yield a singlet resonance at a chemical shift of 3.35 ppm. 1‐D and 2‐DJ‐resolved proton NMR studies (7.0 T) of perchloric acid extracts of brain tissues revealed different amounts ofscyllo‐inositol in man, sheep, cow and rat. Absolute quantification of localized short‐echo time proton NMR spectra (2.0 T) of human brainin vivoresulted inscyllo‐inositol concentrations of 0.35±0.06 mM for white matter (n= 25), 0.43±0.11 mM for grey matter (n= 23) and 0.57±0.14 mM for cerebellum (n= 10). Evidence for a tight metabolic link tomyo‐inositol was supported by a simultaneous variation ofmyo‐ andscyllo‐inositol in patients wit

ISSN:0952-3480    

DOI:10.1002/nbm.1940060116

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY

ISSN:0952-3480    

DOI:10.1002/nbm.1940060101

出版商:John Wiley&Sons, Ltd.    

年代:1993

数据来源: WILEY