Simultaneous observation of glutamate, gamma-aminobutyric acid, and glutamine in human brain at 4.7 T using localized two-dimensional constant-time correlation spectroscopy

Localized two-dimensional constant-time correlation spectroscopy (CT-COSY) was used to resolve glutamate (Glu), gamma-aminobutyric acid (GABA), and glutamine (Gln) in the human brain at 4.7 T. In this method, three-dimensional localization was achieved using three radio frequency pulses of the CT-COSY module for slice selection. As this sequence could decouple JHH along the F1 direction, peak resolution of metabolites was improved even on a magnitude-mode display. In experiments on a phantom containing N-acetylaspartate, creatine, Glu, Gln, and GABA with a constant time delay (Tct) of 110 ms, cross peaks of Glu, Gln, and GABA were obtained on a spectrum processed with standard sine-bell windows, which emphasize sine-dependent signals along the t2 direction. In contrast, diagonal peaks of Glu C4H at 2.35 ppm, GABA C2H at 2.28 ppm, and Gln C4H at 2.44 ppm were resolved on a spectrum processed with Gaussian windows, which emphasize cosine-dependent signals along t2. Human brain spectra were obtained from a 27 mL voxel within the parieto-occipital region using a volume transverse electromagnetic (TEM) coil for both transmission and reception. Tct was 110 ms; the total scan time was 30 min. Diagonal peaks of Glu C4H, GABA C2H, and Gln C4H were also resolved on the spectrum processed with Gaussian windows. These results show that the localized two-dimensional CT-COSY method featuring 1H decoupling along the F1 direction could resolve Glu, GABA, and Gln signals in the human brain.

Peliosis hepatis and neoplastic/dysplastic lesions in aged male Long-Evans Cinnamon rats: MR imaging with pathologic correlation

The Long-Evans Cinnamon (LEC) rat, an animal model of Wilson's disease, abnormally accumulates copper in the liver. There have been a lot of reports on preneoplastic and neoplastic hepatic tumors in LEC rats, but few studies have been focused on other lesions. The aim of this study was to describe the MR findings of the liver of LEC rats with pathologic correlation to characterize the hepatic lesions developed in them. We measured MR images of the liver of six aged (over the age of 70 weeks old) male LEC rats. Measurements of T(1), T(2)-weighted images, and the dynamic and delayed studies after i.v. gadolinium injection were performed. The rats were sacrificed immediately after the measurements, and the diagnosis was histologically made. We identified seven lesions of peliosis hepatis, three neoplastic/dysplastic lesions, three cysts and one cholangiofibrosis. Peliosis hepatis was characterized as showing a significantly long T(2) relaxation time of 57.9 +/- 13.3 ms (mean +/- standard deviation) compared with 41.3 +/- 1.7 ms in normal liver, and prolonged enhancement after a gadolinium injection. Neoplastic/dysplastic lesions tended to show prolonged T(2), and they showed isointensity on T(1)-weighted images. They were best characterized by early enhancement followed by a rapid wash-out after a gadolinium injection. In conclusions, the frequent occurrence of peliosis hepatis observed in the present study suggests this can be a characteristic lesion in aged LEC rats. The characteristic MR findings enable us to distinguish between peliosis hepatis and neoplastic/dysplastic lesions.

Optical isometric force transducer for measurement of rat skeletal muscle contraction in the NMR spectrometer

In order to measure force of contraction of the rat gastrocnemius muscle in the NMR spectrometer with a simultaneous observation of 31P NMR spectra, an optical force transducer was constructed using gratings and optical fibers. Muscle contraction was accurately recorded in the spectrometer without interfering with NMR measurements. The half height width of the phosphocreatine (PCr) peak in the presence or absence of the transducer was 5 Hz. Decrease in PCr and increase in inorganic phosphate (Pi) in the muscle were successfully followed during monitoring of the force developed during exercise. The change in the PCr:(PCr + Pi) ratio correlated well with the time-force integral from the optical force transducer. In general, there was no interference with the 31P NMR spectrum when the transducer was attached to rat leg, so this optical force transducer should prove valuable for studying muscle physiology in the NMR spectrometer.

31P nuclear magnetic resonance study on changes in phosphocreatine and the intracellular pH in rat skeletal muscle during exercise at various inspired oxygen contents

We measured ATP, phosphocreatine (PCr), inorganic phosphate (Pi), and the intracellular pH in rat hindlimb muscles during submaximal isometric exercise with various O2 deliveries using 31P nuclear magnetic resonance spectroscopy (31P NMR) to evaluate changes in energy metabolism in relation to O2 availability. Delivery of O2 to muscles was altered by controlling the fractional concentration of inspired oxygen (F1O2) at 0.50, 0.28, 0.21, 0.11 and 0.08 with monitoring partial pressure of oxygen and carbon dioxide, and bicarbonate at the femoral artery. The steady-state ratio of PCr: (PCr + Pi) during exercise decreased as a function of F1O2 even at 0.21. Significant acidification of the intracellular pH during exercise occurred at 0.08 F1O2. Change in the PCr: (PCr + Pi) ratio demonstrated that the oxidative capacity, i.e. the maximal rate of the oxidative phosphorylation reaction, in muscle was not limited by O2 delivery at 0.50 F1O2, but was significantly limited at 0.21 F1O2 or below. Change in the intracellular pH at 0.08 F1O2 could be interpreted as an increase in lactate, suggesting activation of glycolysis. Correlation between the PCr: (PCr + Pi) ratio and the intracellular pH revealed the existence of a critical PCr: (PCr + Pi) ratio and pH for glycolysis activation at around 0.4 and 6.7, respectively.

MR imaging of non-cancerous hepatic lesions in Long-Evans cinnamon rats

We measured MR images of the liver of Long-Evans Cinnamon (LEC) rats with pathologic correlation and assessed the effectiveness of MR imaging (MRI) for diagnosis of noncancerous hepatic lesions. T1- and T2-weighted images of their livers were obtained, and the dynamic and delayed studies after intravenous gadolinium injection were also performed. Cholangiofibrosis showed low signal intensity on T1-weighted images and high signal intensity on T2-weighted images. The T2 relaxation time of cholangiofibrosis was significantly prolonged (p < .01), and the signal intensity ratio of this lesion to muscle on T1-weighted images was significantly lower than that of normal liver parenchyma to muscle (p < .01). The lesion was enhanced immediately after gadolinium injection and the enhancement was prolonged. Among three cases of peliosis hepatis identified, one showed heterogeneous intensities on both T1- and T2-weighted images and the other two showed similar intensity pattern to cholangiofibrosis. The characteristic MR appearance of cholangiofibrosis may be useful to distinguish it from hepatocellular carcinoma (HCC).

31P NMR study of acute toxic effects of cadmium chloride on rat liver

In this study, acute effects of cadmium ions (Cd2+) on energy metabolism in rat livers were analyzed in vivo after intravenous administration using 31P NMR. Both inorganic phosphate (Pi) and nucleotide triphosphate (NTP) peaks of in vivo Cd-treated livers gradually decreased over a 6-h period. In the extract, NTP peaks in Cd-treated livers were lower, as in the in vivo experiments, but the Pi peak was significantly higher than the control. The apparent decrease in Pi in in vivo liver treated with Cd could be caused by the reduced visibility of Pi because of its uptake into mitochondria from cytoplasm, accompanied by the uncoupling of oxidative phosphorylation by Cd2+. These results indicated that total Pi in the hepatocytes increases after Cd administration. However, only 10% of Pi was visible in Cd-treated livers in vivo, whereas 34% of Pi was visible in controls. Significant increases in phosphocholine and glycerophosphocholine were also observed in extracts of Cd-treated livers.

Proton magnetic resonance imaging and phosphorus-31 NMR studies on the rat brain intoxicated with methyl mercury

Model rats of methyl mercury intoxication were made by orally administering 5 mg mercury/kg methyl mercury daily for 12 days. Proton magnetic resonance imaging and phosphorus-31 nuclear magnetic resonance spectroscopy measurements were performed on the brain of these model animals in vivo under anesthesia. Proton images contrasted with the longitudinal or transverse relaxation times of protons on water and lipid molecules exhibited an internal structure of the poisoned brain. No particular difference was, however, observed between the poisoned and normal control rats in either image. On the other hand phosphorus-31 NMR spectra showed a 17% decrease in phosphocreatine and a corresponding increase in inorganic phosphate in the methyl mercury-poisoned brain. It was also shown that the ATP concentration and the intracellular pH were maintained at a normal level even in the poisoned brain.

Role of cytoplasmic inorganic phosphate in light-induced activation of H(+)-pumps in the plasma membrane and tonoplast of Chara corallina

A unique variant strain of Chara corallina, which contains little inorganic phosphate in the vacuole ([Pi]v) was isolated. The level of cytoplasmic inorganic phosphate ([Pi]c) in these cells was the same as that in normal cells. Using these unique cells, we studied the change in [Pi]c and the effect of Pi on the activities of electrogenic H(+)-pumps associated with the plasma membrane and tonoplast. Upon illumination, the plasma membrane of C. corallina became hyperpolarized by 15 mV, the pH of the vacuolar sap decreased by 0.5 unit, and [Pi]c decreased by 30% with a similar time course. The activities of the electrogenic H (+)-pump in the plasma membrane and the ATP and PPi-dependent H(+)-transport in the tonoplast were noncompetitively inhibited by Pi with Ki values of, in the order given, 21.3 mM, 22.1 mM and 37.7 mM. From the kinetics study we calculated that the electrogenic H(+)-pump in the plasma membrane and the ATP and PPi-dependent H(+) transport in the tonoplast were activated by, again in this order, 13%, 13% and 9%, in accordance with the decrease in [Pi]c. We propose that the change in [Pi]c is one of the regulators of photosynthesis-mediated activation of the H(+)-pumps in the plasma membrane and the tonoplast in C. corallina upon illumination.

Phosphorus-31 nuclear magnetic resonance study on the effects of endurance training in rat skeletal muscle

To evaluate changes in muscle energetics following endurance training, we measured phosphorus-31 nuclear magnetic resonance (31P NMR) spectra on rat muscle in vivo before and after training in the same animals. The endurance training lasted for 3 months. The 31P NMR spectra were obtained serially at rest, during exercise by electrical stimulation, and during recovery. Intramuscular phosphocreatine (PCr), inorganic phosphate (P(i)), adenosine 5'-triphosphate (ATP) and pH were determined from the NMR spectra. The ratio of PCr:(PCR + P(i) at rest showed no difference between the trained and control groups even after 3 months of training. During exercise, however, this ratio was significantly higher in the trained group than in the control group. The ratio also recovered more rapidly after exercise in the trained group. The intramuscular pH decreased slightly by approximately 0.1 pH unit during exercise but did not show a significant difference between the groups. These results indicated that endurance training of 3 months duration improved the ATP supply system in the muscle. They also demonstrated that 31P NMR is a potent method for evaluating the effects of training in the same individuals.

Changes in sarcoplasmic metabolite concentrations and pH associated with the catch contraction and relaxation of the anterior byssus retractor muscle of Mytilus edulis measured by phosphorus-31 nuclear magnetic resonance

The sarcoplasmic concentrations of phosphorus metabolites and pH (pHin) were measured in the anterior byssus retractor muscle (ABRM) of Mytilus edulis by 31P nuclear magnetic resonance spectroscopy. During an active contraction induced by 10(-3) acetylcholine, the concentration of arginine phosphate ([Arg-P]in) decreased from the resting value of 7.47 +/- 0.26 (mean +/- SE, n = 8) to 6.67 +/- 0.29 (n = 6) mumol g-1, and that of inorganic phosphate (Pi) consistently increased from 0.84 +/- 0.06 (n = 7) to 1.61 +/- 0.12 (n = 5) mumol g-1. In the 'catch' state following the active contraction, these concentrations were close to their resting levels, indicating that the catch is an inactive state. 5-hydroxytryptamine caused a rapid relaxation of the catch, which was associated with a slight decrease in [Arg-P]in and an increase in pHin by ca 0.2 units. The sarcoplasmic concentration of ATP (mean, 1.6 mumol g-1) did not change throughout the contraction-relaxation cycle.

Evaluation of exercise muscle energetics by NMR

Magnetic resonance imaging (MRI) is superior to ultrasonography and X-CT especially in density resolution in soft tissue. 31P NMR provides information on metabolism, which has not been obtained in vivo by conventional methods, such as phosphocreatine (PCr), inorganic phosphate (Pi), ATP, and intracellular pH. We used MRI and 31P NMR spectroscopy to study skeletal muscle metabolism of human and rat. These NMR results suggested that 1) estimation of muscle fiber composition, 2) evaluation of muscle ATP turnover and 3) imaging of local muscle fatigue are possible.

Metabolic changes during experimental cerebral ischemia in hyperglycemic rats, observed by 31P and 1H magnetic resonance spectroscopy

Progressive cerebral ischemia was induced in seven anesthetized hyperglycemic rats by carotid artery ligation and hemorrhagic hypotension. Phosphorus metabolites, intracellular pH, and lactate in the brain were monitored by 31P and 1H magnetic resonance spectroscopy. Under conditions in which blood flow was low, phosphocreatine (PCr) concentration and intracellular pH decreased and the concentration of lactate increased. The decrease in ATP was approximately one-third that of PCr until only 25% PCr remained, after which ATP was lost more rapidly than PCr. These changes were interpreted in terms of three regions observed by the magnetic resonance coil, one of complete ischemia, one of partial ischemia, and one of perfusion sufficient to maintain normal metabolite levels. The extent of the three regions was estimated quantitatively. Broadening and splitting of the inorganic phosphorus (Pi) peak into two components provided further evidence of distinct populations of cells, one very acidic and another less so. Apparent intracellular buffering capacity was calculated as 23.6 +/- 1.3 mumol lactate/g wet wt/pH.

31P-NMR saturation transfer studies of aerobic Escherichia coli cells

31P-NMR measurements of saturation transfer have been used to measure the flux between Pi and ATP in Escherichia coli cells respiring on an endogenous carbon source. Measurements were made in the wild type and in cells genetically modified to give a 5-fold higher concentration of the F1F0-ATP synthase. The flux in the two cell types was not significantly different. This, together with studies using inhibitors specific for the glycolytic enzyme, glyceraldehyde-3-phosphate dehydrogenase and the ATP synthase, suggests that the observed flux arises predominantly from glycolytic rather than ATP synthase activity. Although this conclusion is in disagreement with previous experiments on E. coli, it is in agreement with recent experiments on yeast.

Photophosphorylation and oxidative phosphorylation in intact cells and chromatophores of an aerobic photosynthetic bacterium, Erythrobacter sp. strain OCh114

Light-induced ATP synthesis was studied in intact cells and chromatophores of Erythrobacter sp. strain OCh114. ATP synthesis was measured by both the pH method and the luciferin-luciferase luminescence method. The rate of ATP synthesis was moderate (a typical value of 0.65 mol of ATP per mol of bacteriochlorophyll per min), and synthesis was inhibited by antimycin A. ATP was synthesized under illumination only under aerobic conditions and not under anaerobic conditions. This characteristic was similar to that of other light-induced energy transduction processes in this bacterial species, such as oxidation of reaction center, oxidation of cytochrome c551, and translocation of H+, which were not observed under anaerobic conditions. This phenomenon was reconciled with the fact that the Erythrobacter sp. could not grow anaerobically even in the light. The characteristics of oxidative phosphorylation and ATP hydrolysis were also investigated. The respiratory ratio of chromatophores was 2.3. Typical rates of oxidative phosphorylation by NADH and by succinate were 2.9 mol of ATP per mol of bacteriochlorophyll per min (P/O = 0.22) and 1.1 mol of ATP per mol of bacteriochlorophyll per min (P/O = 0.19), respectively. A typical rate of ATP hydrolysis was 0.25 mol of ATP per mol of bacteriochlorophyll per min in chromatophores. ATPase and adenylate kinase are also involved in the metabolism of adenine nucleotides in this bacterium.

Phosphorus-31 nuclear magnetic resonance studies on intact erythrocytes. Determination of intracellular pH and time course changes in phosphorus metabolites

A method to determine the intracellular pH of intact erythrocytes using phosphorus-31 nuclear magnetic resonance spectroscopy is described. Changes in phosphorus metabolites due to the alkalization of intracellular pH were also examined. The normal erythrocytes gave signals of phosphate groups corresponding to 2,3-bisphosphoglycerate, inorganic phosphate, ATP, and NAD. Among them, the separation between alpha and gamma peaks of ATP was shown to be a good indicator of the intracellular pH free from the perturbation caused by hemoglobin. This method enabled us to determine the intracellular pH of the erythrocytes without any pretreatment. The separation between alpha and gamma peaks of ATP was also dependent on the degree of complexation with Mg2+, and was consistent with approximately 80% of total ATP complexing with Mg2+ in the samples investigated here. The pKa value of ATP in the erythrocytes was estimated to be 6.1 at 23 degrees C, which is lower than the value of 6.5 obtained for the Mg2+-free ATP solution. In the alkalized erythrocytes, fructose 1,6-bisphosphate and dihydroxyacetone phosphate were observed in addition to the metabolites found in the normal erythrocytes. Time course changes in these phosphorus metabolites were followed along with the intracellular pH monitored from ATP peaks.

Proton nuclear magnetic resonance studies of mammalian metallothioneins

Proton nuclear magnetic resonance studies of various mammalian metallothioneins are described. Metallothioneins-1 and 2, isolated from rat and rabbit, and also metallothionein-2, from humans, were investigated. Proton NMR spectra showed that mammalian metallothioneins containing Cd have similar tertiary structures regardless of their sources. On the other hand, metallothioneins containing both Cd and Zn have a slightly different conformation from those containing Cd alone. Almost all methyl resonances of Cd-metallothioneins were assigned to those of Met, Ile, Leu, Val, Thr, and Ala residues by NMR double resonance techniques, pH titration, and the spectral comparison of these metallothioneins. alpha-Proton resonances of Ala residues were classified into two groups, one of which arose around 4.1 ppm, the other around 4.4 ppm. Moreover, the number of alpha-proton resonances around 4.1 ppm and 4.4 ppm agreed with the number of Ala residues in the COOH-terminal and NH2-terminal domains of the metallothionein, respectively. This finding suggests that the chemical shift values of alpha-protons of Ala residues are reflective of the domain structure of the metallothioneins.