Investigation on the cation location,structure and performances of rare earth-exchanged Y zeolite

A series of Y zeolites exchanged with different amount of cerium and lanthanum cations were investigated. Comprehensive routine analysis tools including X-ray photoelectron spectroscopy(XPS), X-ray fluorescence(XRF), X-ray diffraction(XRD) and Py-Fourier transform infrared spectroscopy(Py-FTIR) were used to identify the cation location, and the result was verified via XRD Rietveld study. The results revealed that almost all the RE cations in RE-4, most cations in RE-8 to RE-14 and part of cations in RE-16 were located in the sodalite cage. The Al~(IV)/(Al~V+Al~(VI)) values revealed by ~(27)Al MAS NMR spectra, the silicon aluminum ratio of the framework(SARF) values deduced from ~(29)Si MAS NMR spectra and XRD, and hydroxyl amount were reasonably in accordance with the location and content of rare earth cations. The hydrothermal stability derived from in situ XRD investigation and catalyst activity provided by micro-activity test manifested that samples RE-8 to RE-14 exhibited better performances than RE-4 and RE-16, among which RE-12 had the best properties. The phenomena were interpreted by the cation location and structural properties.     

Off-resonance nutation nuclear magnetic resonance study of framework aluminosilicate glasses with Li, Na, K, Rb or Cs as charge-balancing cation

Framework aluminosilicate glasses with varying charge-balancing cation (Li, Na, K, Rb and Cs) have been studied with 27Al and 29Si magic-angle spinning nuclear magnetic resonance (MAS NMR) and 27Al on-resonance and off-resonance nutation NMR spectroscopy. This first application of off-resonance nutation NMR to disordered samples proves that it is a promising technique for the determination of mean quadrupole interactions in amorphous systems. Linewidths for Al decrease systematically with increasing size of the cation, due to a decrease in the quadrupole interaction from 5.0 MHz for the Li glass to 2.8 MHz for the Cs glass. A simple point-charge model effectively predicts the decrease in the quadrupole interaction. This indicates that the alkali ion is located close to aluminum. Looking at the residual linewidth after subtraction of the quadrupole broadening, the Al chemical shift distribution does not change significantly with the type of alkali ion. The same is true for the observed Si linewidth.     

29Si CP/MAS NMR of phosphorus-bearing organosilicon compounds

While liquid-state 29Si NMR of phosphorus-bearing organosilicon compounds with more than one phosphorus per molecule can take advantage of the presence of J-coupling nJ(31P29Si) for purposes of structural assignment from J-coupling patterns, conventional 29Si CP/MAS spectra of such molecular solids do not reveal structural details in a straightforward manner. For such compounds it is necessary to obtain 29Si CP/MAS spectra under conditions of simultaneous 1H- and 31P-high power decoupling in order to derive reliable 29Si chemical shift information. 29Si CP/MAS NMR spectra, obtained with and without 31P high power decoupling during the acquisition time, of several organosilicon compounds containing SixPy (x = 1-10, y = 1-10) moieties are reported.     

1H MAS and 1H[23Na] double resonance NMR studies on the modification of surface hydroxyl groups of gamma-alumina by sodium

The modification of surface hydroxyl groups with sodium in a series of Na2CO3-gamma-Al2O3 catalysts was investigated as a function of both the Na2CO3 loading and the calcination temperature by means of 1H magic angle spinning (MAS) and 1H(23Na) spin-echo double resonance NMR techniques. The 1H NMR experiments revealed that sodium ions are homogeneously distributed over the alumina surface and closely coordinated with the surface hydroxyl groups. In the catalysts calcined at 250 degrees C, the acidic hydroxyl groups (with a chemical shift of 2.0 ppm) are preferentially associated with sodium ions at low Na2CO3 coverages (5 and 10%), while both the acidic and the basic (0 ppm) hydroxyl groups are accessible for sodium ions at high coverages (15 and 20%). The coordination causes a low-field shift of about 2 ppm in the 1H MAS spectra, and a broad signal at 4.5 ppm appears. It is interesting that the 4.5 ppm signal is completely suppressed in the 1H(23Na) MAS experiments, providing direct evidence that a strong interaction exists between adsorbed sodium ions and the surface hydroxyl groups. Increasing the calcination temperature to 450 degrees C results in preferential removal of the acidic hydroxyl groups, and only the most basic hydroxyl groups remain when the calcination temperature is raised to 600 degrees C. This is attributed to the formation of the coordinated species. [formula: see text] which enhances the acidity of the surface hydroxyl groups and prompts their dehydroxylation, especially at high calcination temperature. Correlation of the 1H MAS NMR results and catalytic activity measurements indicates that the basic hydroxyl groups are essential for the carbonyl sulfide hydrolysis reaction.     

Lactate turnover in rat glioma measured by in vivo nuclear magnetic resonance spectroscopy

Elevated tissue lactate concentrations typically found in tumors can be measured by in vivo nuclear magnetic resonance (NMR) spectroscopy. In this study, lactate turnover in rat C6 glioma was determined from in vivo 1H NMR measurements of [3-13C]lactate buildup during steady-state hyperglycemia with [1-13C]glucose. With this tumor model, a narrow range of values was observed for the first-order rate constant that describes lactate efflux, k2 = 0.043 +/- 0.007 (n = 12) SD min-1. For individual animals, the standard error in k2 was small (< 18%), which indicated that the NMR data fit the kinetic model well. Lactate measurements before and after infusing [1-13C]glucose showed that the majority of the tumor lactate pool was metabolically active. Signals from 13C-labeled glutamate in tumors were at least 10-fold smaller than the [3-13C]lactate signal, whereas spectra of the contralateral hemispheres revealed the expected labeling of [4-13C]glutamate, as well as [2-13C] and [3-13C]glutamate, which indicates that label cycled through the tricarboxylic acid cycle in the brain tissue. Lack of significant 13C labeling of glutamate was consistent with low respiratory metabolism in this glioma. It is concluded that lactate in rat C6 glioma is actively turning over and that the kinetics of lactate efflux can be quantified noninvasively by 1H NMR detection of 13C label. This noninvasive NMR approach may offer a valuable tool to help evaluate tumor growth and metabolic responsiveness to therapies.     

Reaction paths of iron oxidation and hydrolysis in horse spleen and recombinant human ferritins

UV-visible spectroscopy, electrode oximetry, and pH stat were used to study Fe(II) oxidation and hydrolysis in horse spleen ferritin (HoSF) and recombinant human H-chain and L-chain ferritins (HuHF and HuLF). Appropriate test reactions and electrode responses were measured, establishing the reliability of oxygen electrode/pH stat for kinetics studies of iron uptake by ferritin. Stoichiometric ratios, Fe(II)/O2 and H+/Fe(II), and rates of oxygen uptake and proton production were simultaneously measured as a function of iron loading of the protein. The data show a clear distinction between the diiron ferroxidase site and mineral surface catalyzed oxidation of Fe(II). The oxidation/hydrolysis reaction attributed to the ferroxidase site has been determined for the first time and is given by 2Fe2+ + O2 + 3H2O --> [Fe2O(OH)2]2+ + H2O2 + 2H+ where [Fe2O(OH)2]2+ represents the hydrolyzed dinuclear iron(III) center postulated to be a mu-oxo-bridged species from UV spectrometric titration data and absorption band maxima. The transfer of iron from the ferroxidase site to the mineral core has been now established to be [Fe2O(OH)2]2+ + H2O --> 2FeOOH(core) + 2H+. Regeneration of protein ferroxidase activity with time is observed for both HoSF and HuHF, consistent with their having enzymatic properties, and is facilitated by higher pH (7.0) and temperature (37 degreesC) and by the presence of L-subunit and is complete within 10 min. In accord with previous studies, the mineral surface reaction is given by 4Fe2+ + O2 + 6H2O --> 4FeOOH(core) + 8H+. As the protein progressively acquires iron, oxidation/hydrolysis increasingly shifts from a ferroxidase site to a mineral surface based mechanism, decreasing the production of H2O2.     

Quantitation of intracellular [Na+] in vivo by using TmDOTP5- as an NMR shift reagent and extracellular marker

A method is presented to measure the absolute concentration of intracellular Na+ ([Na+]i) in vivo by using interleaved 23Na- and 31P-nuclear magnetic resonance (NMR) spectroscopy and TmDOTP5- as shift reagent and chemical marker of tissue extracellular space (ECS). The technique was used to determine [Na+]i and relative ECS in livers of control rats (21 +/- 3 and 0.11 +/- 0.02 mM, respectively) and in rats exposed to carbon tetrachloride (103 +/- 29 and 0.23 +/- 0.03 mM, respectively). The NMR measurements were confirmed independently on excised tissue samples by using atomic absorption spectroscopy. The results confirm that TmDOTP5- can be used as a combined cation shift reagent and ECS marker, thereby allowing quantitation of [Na+]i in vivo by NMR.     

Preparation and steric structure elucidation of saturated or partially saturated isoindolo[2,1-a][3,1]benzoxazinones, -[1,2-b][2,4]benzoxazepinones, cyclopentane- and -cyclohexane[b]pyrrolo[2,1-a][3,1]-benzoxazines

The reactions of 2-carboxybenzaldehyde (1) with 1,3- or 1,4-aminoalcohols (2a-i, 3a,b) were used to prepare partially or fully saturated tetra- and pentacyclic compounds containing a condensed 1,3-oxazino- or oxazepinoisoindolone moiety and one terminal saturated carbocycle. Isoindolo[2,1-a][3,1]benzoxazinones (4a-d, 6, 7), stereoisomeric isoindolo[1,2-b][2,4]benzoxazepinones (5a-c) hexahydrocyclopentane[b]pyrrolo[1,2-a][3,1]-benzoxazinone (10a,b), octahydroindolo[1,2-b]- and decahydroindolo[1,2-a]benzoxazinone (11a,b and 12a,b) and related pentacyclic derivatives (4e-g) were prepared. The diastereomers 5a-c differ in the ring annelation or in the position of the NCHO hydrogens and annelational hydrogens. The stereostructures of these compounds were elucidated by means of 1H and 13C NMR spectroscopy, including DNOE, DEPT, 2D-HSC measurements and X-ray analysis.     

Nuclear medicine in the diagnosis of osteoarticular diseases (author''s transl)

1. The effect of Na and K ions on active Na transport was studied in guinea-pig auricles by means of flame photometry. 2. The Na influx into preparations rewarmed in Tyrode's solution after cooling was estimated to be about 1.05 mmole/l fibre water - min (l.f.w.-min) or c. 8 pmole/cm2 - s. Intracellular Na ions enhanced the active Na efflux over a wide range of concentrations. A decrease in the extracellular Na concentration ([Na]o) had no major effect on the active Na efflux. 3. Extracellular K ions initiated an active Na efflux from rewarmed auricles with an elevated [Na[i over a narrow range of K concentrations ([K]o). 4. Assuming Michaelis-Menten kinetics the maximal active Na efflux activated by internal Na ions was calculated to be about 4 mmole/l.f.w. - min (30 pmole/cm2 - s). Half maximal Na efflux occurred at about 22 mmole/l.f.w. [Na]i. The maximal K-activated active - min (28 pmole/cm2 - s) and was half maximal at a [K]o of about 0.2 mM. 5. It is tentatively concluded that the maximal active Na efflux from guinea-pig atria is 3--4 times larger than the physiological flux. Under normal conditions active Na efflux in heart is mainly regulated by variations of [Na]i.     

120 t RH自然脱碳精炼低碳钢QD08的生产实践

基于生产数据对120 t RH精炼低碳钢QD08(/%:≤0.07C,0.15～0.35Si,0.25～0.45Mn,≤0.035P,≤0.035S)进行了RH碳氧反应的热力学、动力学分析和自然脱碳分析,得出RH精炼自然脱碳的优化工艺。结果表明,BOF终点温度≥1650℃,RH初始温度≥1 600℃,BOF终点[C]0.04%～0.10%,[P]≤0.018%,出钢前加顶浇石灰200 kg,出钢不加合金和脱氧剂,RH真空度4～8 kPa,6～8 min可使钢水[C]≤0.05%。     

改性合成方钠石对重金属离子Cu2+、Pb2+的吸附

采用水热合成法以高岭石为原料合成方钠石,并将合成的方钠石用盐酸和双氧水改性。利用SEM、XRD和BET等对产物进行表征,对比了不同合成条件下的方钠石的组织形态以及微观结构的变化,研究了不同改性下条件方钠石对重金属离子Cu2+、Pb2+的吸附性能。结果表明:HTPS、HA-HTPS和HP-HTPS的比表面积分别为104.78、112.64、127.71 m2/g,三者的平均孔径相差不大。HTPS、HA-HTPS、HP-HTPS对Cu2+和Pb2+的理论最大吸附量分别为61.73、251.89、62.85 mg/g和265.95、65.88、283.29 mg/g,三者对2种重金属离子的吸附等温线均符合Langmuir吸附等温模型,该研究提供了一种应用合成与改性方钠石高效去除水体重金属离子的方法。      

Kinetics of Na(+)-dependent conformational changes of rabbit kidney Na+,K(+)-ATPase

The kinetics of Na(+)-dependent partial reactions of the Na+,K(+)-ATPase from rabbit kidney were investigated via the stopped-flow technique, using the fluorescent labels N-(4-sulfobutyl)-4-(4-(p-(dipentylamino)phenyl)butadienyl)py ridinium inner salt (RH421) and 5-iodoacetamidofluorescein (5-IAF). When covalently labeled 5-IAF enzyme is mixed with ATP, the two labels give almost identical kinetic responses. Under the chosen experimental conditions two exponential time functions are necessary to fit the data. The dominant fast phase, 1/tau 1 approximately 155 s-1 for 5-IAF-labeled enzyme and 1/tau 1 approximately 200 s-1 for native enzyme (saturating [ATP] and [Na+], pH 7.4 and 24 degrees C), is attributed to phosphorylation of the enzyme and a subsequent conformational change (E1ATP(Na+)3-->E2P(Na+)3 + ADP). The smaller amplitude slow phase, 1/tau 2 = 30-45 s-1, is attributed to the relaxation of the dephosphorylation/rephosphorylation equilibrium in the absence of K+ ions (E2P<==>E2). The Na+ concentration dependence of 1/tau 1 showed half-saturation at a Na+ concentration of 6-8 mM, with positive cooperatively involved in the occupation of the Na+ binding sites. The apparent dissociation constant of the high-affinity ATP-binding site determined from the ATP concentration dependence of 1/tau 1 was 8.0 (+/- 0.7) microM. It was found that P3-1-(2-nitrophenyl)ethyl ATP, tripropylammonium salt (NPE-caged ATP), at concentrations in the hundreds of micromolar range, significantly decreases the value of 1/tau 1, observed. This, as well as the biexponential nature of the kinetic traces, can account for previously reported discrepancies in the rates of the reactions investigated.     

Preparation and Characterization of Hybrid Luminescence Mesoporous MCM-48 Doped with Eu( Ⅲ ) Complex

The preparation of hybrid mesoporous MCM-48 grafted by vinyl group via post-grafting process was reported and studied by X-ray diffraction, BET and 29Si solid MAS NMR.An organic β-diketonate Europium complex the corresponding luminescence property was characterized.     

Kinetics of the competitive degradation of deoxyribose and other biomolecules by hydroxyl radicals produced by the Fenton reaction

The objective of this work is to reexamine the competitive degradation of deoxyribose by hydroxyl radicals (.OH) produced by the reaction between H2O2 and Fe(2+)-EDTA. The .OH radicals produced attack deoxyribose (D, rate constant kD) and eventually an .OH scavenger (S, rate constant kS). First, we examined the effect of [D], [H2O2], [Fe(2+)-EDTA], [EDTA]/[Fe2+] ratio and reaction time on the rate of D degradation, measured as the absorbance of the chromogen formed between the product of the reaction D + .OH (malondialdehyde) and thiobarbituric acid. In particular, it was showed that under our experimental conditions ([D] = 3 mM, [H2O2] = 0.85 mM, [Fe2+] = 0.13 mM), the rate of overall process is first order in Fe2+, zero order in H2O2 and is maximal for a ratio [EDTA]/[Fe2+] = 1.1. Second, the kinetics of .OH radical reaction in competition experiments between D and S (mannitol) was investigated. The results show that the ratio of the rates of D degradation in the absence (VD) and in the presence (VDS) of S should be represented by VD/VDS = 1 + ks[S]/(kD[D] + kx) where kx accounts for the rate of .OH reactions with other reagents such as Fe(2+)-EDTA, H2O2 etc . . . After having determined kx for each set of experimental conditions, we obtained the values of kS/kD by determining the variations of VD/VDS as a function of [S] and [D]. By taking kD = 1.9 x 10(9) M-1s-1 a value of kS = 1.9 x 10(9) M-1s-1 was obtained, very close to that obtained by pulse radiolysis. Finally, the validity of the established relation was confirmed for other biomolecules (methionine, k = 5.6 x 10(9)M-1s-1 and alanine, k = 3.3 x 10(8) M-1s-1). By contrast, it was not applicable to cysteine, thiourea and mercaptoethanol which was attributed to an interaction of the latter scavengers with Fe2+ and/or H2O2.     

Cognitive and functional assessments of stroke patients: an analysis of their relation

We have examined the reactions of peroxynitrite with short-chain aliphatic aldehydes to model the reaction of the peroxynitrite anion (ONOO-) with CO2. Aldehydes, like CO2, react rapidly with peroxynitrite and catalyze its decomposition. The pH dependence of the reaction is consistent with the addition of ONOO- (not ONOOH) to the carbonyl carbon atom of the free aldehyde forming a 1-hydroxyalkylperoxynitrite anion adduct (5), which structurally resembles the nitrosoperoxycarbonate adduct (1) formed from the reaction of ONOO- with CO2. Intermediate 5, or the secondary products derived from it, decays to give NO3- and regenerated aldehyde, with small but significant yields of H2O2, organic acids, and organic nitrates. In analogy with the peroxynitrite/CO2 system, it is suggested that 5 undergoes homolytic or heterolytic cleavage at the O-O bond, giving a caged radical pair [RCH(OH)O./ .NO2] (7) or intimate ion pair [RCH(OH)O -/+ NO2] (8). The radicals and ions in intermediates 7 and 8 can recombine within the solvent cage to form 1-hydroxyalkylnitrate [RCH(OH)ONO2] (6), which can then dissociate to give nitrate and regenerate the aldehyde. The aldehyde/ peroxynitrite adducts 5-8 mediate the oxidation of 2,2'-azinobis(3-ethylbenzthiazoline-6-sulfonate) but not the nitration of 4-hydroxyphenylacetate. The significance of these findings is discussed in relation to the mechanism(s) of the CO2-catalyzed isomerization of peroxynitrite to nitrate and biological nitrations involving peroxynitrite/CO2 adducts.     

X20Cr13钢材成分对力学性能影响的回归分析

对钢厂6 t电弧炉+LF+VOD+3 t ESR生产的40 mm×40 mm~80 mm×80 mm X20Cr13不锈钢方钢棒材（/%:0.17~0.22C,0.30~0.80Mn,0.10~0.50Si,0.30~0.80Ni,12.5~14.0Cr)随机抽取89炉次,进行化学成分与力学性能的统计回归分析,得到了该类钢材成分与其力学性能的定量回归关系式:σ_s=704.9+121.9[Ni]-84.9[Mn];σ_b=638.7+51.1[Ni]-40.5[Mn]+16.9[Cr];A=81.8-24.8[C]+2.7[Mn]-4.4[Cr];Z=49.4+47.5[C]+4.8[Si]+4.3[Ni];AKV=-90.8-55.8[Mn]+10.2[Cr]+154.1[Si]。如工艺参数和棒材规格等因素改变时,应重新回归分析,修正方程系数。     

Calcium-sodium antagonism on the frog's heart: a voltage-clamp study

1. In double sucrose-gap voltage-clamped frog atrial fibres the influence of [Ca]o and [Na]o on membrane current and contraction was investigated. 2. The slow (secondary) inward current varied with [Ca]o but was almost insensitive to changes in [Na]o. In contrast, the phasic (transient) contraction initiated by the slow inward current was affected by both [Ca]o and [Na]o. 3. With moderate changes of [Ca]o and [Na]o from normal, the strength of phasic contraction at a given depolarization followed the [Ca]o/[Na]2o ratio approximately. This was best seen at membrane potentials near zero level. 4. Under the same conditions, tonic (sustained) contractions associated with prolonged depolarizations were strictly correlated to the [Ca]o/[Na]2o ratio at any potential. No interrelation between tonic tension and steady-state current was found. 5. With extensive changes in [Ca]o and [Na]o, the sensitivity of both phasic and tonic tension to the [Ca]o/[Na]2o ratio declined, the negative effect of [Na]o becoming smaller than was expected from this ratio. 6. In Na-free choline-Ringer, a strong contracture developed followed by a spontaneous relaxation. Starting from the relaxed state, application of depolarizing clamps gave rise to phasic contractions with a very slow relaxation while tonic contractions were apparently lacking. 7. The results are interpreted in terms of an energy-dependent carrier mechanism exchanging one Ca for two Na ions across the cell membrane. The model implies a strong asymmetry in the rate constants governing the chemical reactions on both sides of the membrane. The system is thought to operate close to equilibrium at any potential, thereby determining the steady level of myoplasmic Ca. The equilibrium itself is considered to shift upon depolarization. Assuming that [Na]i is constant, the steady level of [Ca]i is expected to be proportional to the [Ca]o/[Na]2o ratio, the scale factor being a function of membrane potential. 8. The carrier model suggests the occurrence of a depolarization-induced inward transfer of Ca which might be involved in the generation of tonic contractions. 9. The apparent lack of tonic contractions in the absence of external Na ions may be explained by a suppression of carrier-mediated Ca influx normally occurring upon depolarization. 10. The antagonistic effects of [Ca]o and [Na]o on phasic contraction are understood as being due to alterations of the Ca pumping system rather than changes in slow inward current.     

Probing the mechanism of inosine monophosphate dehydrogenase with kinetic isotope effects and NMR determination of the hydride transfer stereospecificity

The mechanism of human type II inosine monophosphate dehydrogenase has been probed by measurements of primary deuterium kinetic isotope effects, and by determination of the stereochemical course of the reaction. The deuterium isotope effects on Vmax from [2-deutero]-IMP are unity for reactions with a variety of monovalent cation activators (K+, NH4+, Na+, Rb+) of various efficacy. In each case normal effects on Vmax/K(m) in the range of 1.9 to 3.5 are observed for both IMP and NAD, and are larger for NAD. These results demonstrate that both substrates can dissociate from the E.M+.IMP.NAD complex, therefore the kinetic mechanism is not ordered as previous steady-state kinetic studies have suggested. Comparison of reaction rates in D2O and H2O show no 2H isotope effect on Vmax, and a < or = twofold decrease in Vmax/K(m); thus, a proton transfer from solvent is not rate-limiting in turnover. The NMR spectrum of the [4-deutero]NADH produced in the reaction of [2-deutero]-IMP and NAD shows that the hydrogen is transferred to the B, or pro-S, side of the nicotinamide ring. Presteady-state kinetic experiments reveal a burst of NADH formation in the first turnover, demonstrating that a late step in the mechanism is rate-limiting. The rate of the burst phase is reduced approximately twofold with [2-deutero]IMP as substrate, indicating that the hydride transfer step is kinetically significant early in the reaction.     

Effects of ischemia on intracellular sodium and phosphates in the in vivo rat liver

Metabolic factors that influence the transition form reversible to irreversible ischemic injury were studied in the rat liver in vivo with 31P-nuclear magnetic resonance (NMR) spectroscopy. Hepatic ischemia for 15, 35, or 65 min was produced by occlusion of the hepatic artery and portal vein in rats. Ischemia caused a rapid decrease in the ATP concentration ([ATP])-to-P(i) concentration ratio and pH within 5 min, but there was little change in these variables detectable by 31P-NMR with longer periods of ischemia. After reperfusion, the [ATP] and P(i) concentration returned toward normal values in livers exposed to 15 or 35 min of ischemia, but 65 min of ischemia were associated with only modest recovery in [ATP], and the [ATP] later decreased. Because the 31P-NMR spectrum was similar after brief compared with prolonged ischemia, it appears that neither ATP depletion, P(i) accumulation, nor acidosis predicts metabolic recovery. Hepatic intracellular NA+ was also measured in separate groups of animals by 23Na-NMR in the presence of a shift agent, thulium (III) 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetrakis (methylene-phosphonate) (TmDOTP5-), and by atomic absorption spectroscopy. Under baseline conditions, the concentration of intracellular Na+ was 15.2 mM by atomic absorption spectroscopy and 16.5 mM by 23Na-NMR. Although the 31P-NMR spectrum responded very rapidly to the onset of ischemia, intracellular Na+ concentration measured by 23Na-NMR increased gradually but steadily at approximately 1.0 mM/min during early (up to 15 min) ischemia. These observations demonstrate that a rise in intracellular Na+ does occur early ischemia, that TmDOTP5- can be applied in vivo for analysis of intracellular Na+ in the ischemic liver, and that 31P-NMR spectroscopy is very sensitive to early ischemic injury.     

Importance of the early alterations of energy metabolism in the induction and the disappearance of ischemic preconditioning in the isolated rat heart

The kinetics of alterations in high energy phosphates were studied in isolated rat hearts during single and multiple ischemic preconditioning (IPC) using [31P]-nuclear magnetic resonance (NMR) spectroscopy. Aortically perfused hearts were subjected to a 25 min sustained ischemia and a 30 min reperfusion. The IPC protocols used a basic pattern of 3 min ischemia plus 6 min reflow, increasing the reflow period from 6 to 12 min. Efficient IPC was associated during ischemia with a reduction in ATP degradation, in intracellular acidosis and a maintenance of a residual pool of PCr. Analysis of the IPC phase showed that each short ischemia was followed by a vasodilation (40-50%), accompanied by a clear PCr overshoot (115-125%) and a cytosolic Pi undershoot. Thus, the energy producing reactions were swung out of their initial equilibrium. The PCr overshoot remained up to the onset of the sustained ischemia in the efficient protocols, whereas it has practically vanished in the unefficient ones. In addition, the duration of such a positive imbalance appeared reinforced and prolonged by multiple IPC. It is suggested that an IPC cycle induced a time-dependent positive imbalance in the mitochondrial oxphosphorylative reactions. The benefit for the heart developed only when the prolonged ischemia was imposed under such conditions, modifying thereby the early dynamics of the energy metabolism processes during the initial phase of the sustained ischemia.