Exploration of Na<Superscript>+</Superscript>,K<Superscript>+</Superscript>-ATPase ion permeation pathways <Emphasis Type="Italic">via</Emphasis> molecular dynamic simulation and electrostatic analysis

Biologically-inspired nanodevices can serve as “natural” alternatives to conventional semiconductor devices in many applications from information storage to mechanical rotors. In this work we consider an ATP-powered transmembrane protein, the Na⁺,K⁺-ATPase, which has appealing functionality but still lacks an “atomistic” picture capable of elucidating its operation. The vast collection of experimental literature on the Na⁺,K⁺-ATPase gives a unique advantage to this protein in developing and validating computational tools. We have performed extensive molecular dynamic simulations of the Na⁺,K⁺-ATPase in an accurate biological environment, followed by time-averaged electrostatic analysis, to investigate the ion-binding loci and access/egress pathways that cations may take through the protein as they are transported across the membrane.     

Multinuclear MR-spectroscopy on ion-homeostasis and energetics during ischemia and reperfusion

4. Conclusion Voltage-gated Na⁺-channels constitute a major port of Na⁺ entry in the initial minutes following the onset of ischemia. The persistent component of the Na⁺ current does not play a significant role in the guinea pig heart even thereafter. Due to intracellular acidification. NHE is activate dand forms the dominant influx pathway in the next 30 min of ischemia, but is partially inactivated in the later course of ischemia. Alternative, not yet characterised ports of entry gain importance in this phase. Blocking either voltage-gated Na⁺-channels or NHE improved post-ischemic contractile function. Thus reducing Na⁺-overload in ischemia (and reperfusion) is a promising therapeutical aporoach for cardio-protection.     

Synthesis and temperature-dependent optical properties of Eu3+-doped NaYSiO4 red-emitting phosphors

Abstract

Novel Eu³⁺-activated orthosilicate NaYSiO₄:xEu³⁺ (x?=?0.02, 0.05, and 0.20) red-emitting phosphors were developed for white light emitting diode applications. The X-ray diffraction (XRD), photoluminescence excitation and emission spectra, temperature-dependent curves were applied to characterize the samples. The red emission of the NaYSiO₄:Eu³⁺ phosphor corresponding to ⁵D₀→⁷F₂ (614?nm) transition was observed under the excitation of 394?nm wavelength, which is suitable for UV LED chip. The quenching temperature for NaYSiO₄:0.05Eu³⁺ was found to be over 500 K. The CIE chromaticity coordinates of NaYSiO₄:0.05Eu³⁺ are very close to the National Television System Committee (NTSC) standard red.     

The Role of Long-Range Forces in Porin Channel Conduction

A fully self-consistent 3D Poisson P³M Brownian dynamics solver is used to investigate the role of the long-range electrostatic forces on the selectivity and conductivity of OmpF porin. Our simulations show that even with zero applied bias, the long-range interactions are an important component of the total potential energy. In addition, the long-range force due to mobile carriers is shown to play a role in facilitating the flow of anions through the OmpF channel by screening the effect of the negative fixed charge of the protein.     

Quantification of metabolites from single-voxelin vivo 1H NMR data of normal human brain by means of time-domain data analysis

We present here a combination of time-domain signal analysis procedures for quantification of human brainin vivo ¹H NMR spectroscopy (MRS) data. The method is based on a separate removal of a residual water resonance followed by a frequency-selective time-domain line-shape fitting analysis of metabolite signals. Calculation of absolute metabolite concentrations was based on the internal water concentration as a reference. The estimated average metabolite concentrations acquired from six regions of normal human brain with a single-voxel spin-echo technique for theN-acetylaspartate, creatine, and choline-containing compounds were 11.4±1.0,6.5±0.5, and 1.7±0.2 mmol kg^–1 wet weight, respectively. The time-domain analyses ofin vivo ¹H MRS data from different brain regions with their specific characteristics demonstrate a case in which the use of frequency-domain methods pose serious difficulties.     

Contribution of various substrates to total citric acid cycle flux and ]anaplerosis as determined by13C isotopomer analysis and O2 consumption in the heart

A simple relationship between parameters derived from a¹³C NMR isotopomer analysis and O₂ consumption is presented that allows measurement of the absolute rate of acetyl-CoA oxidation and anaplerotic flux in tissues oxidizing a mixture of four substrates. The method was first applied in a study of the effects of work state and -adrenergic stimulation on net acetate oxidation and anaplerosis in the isolated working rat heart. The results demonstrate that the anticipated ratio of 2 between O₂ consumption and TCA cycle flux for hearts oxidizing only acetate holds at low workload when anaplerosis is low, but deviates toward a factor of 3 under high workload conditions when anaplerosis is increased. This analysis was also extended to hearts that oxidize a more physiological mixture of substrates including long-chain fatty acids, acetoacetate, lactate, pyruvate, and glucose. We show that the contribution each substrate makes to total TCA cycle flux can be determined by combined¹³C NMR and O₂ consumption measurements. The present study also demonstrates that stimulation of anaplerosis (by addition of propionate) can significantly alter the relative contribution each substrate makes to total TCA cycle flux. We conclude that if¹³C labeling patterns are selected appropriately, a comprehensive picture of flux through all major metabolic pathways feeding the cycle can be determined in a single experiment even when complex physiological mixtures of substrates are provided.     

220 kV GIS SF6 CT气室闪络分析

通过常规与非常规化学、电气试验手段,对GIS SF6 CT气室中闪络故障前后固体粉末、气体成分及CT气室内的化工材料进行排查试验,证明频繁发生闪络故障的内置式CT气室内存在丁腈橡胶板,其腐蚀性硫与气室内触头等镀银件反应形成硫化银,最终形成导电通道,引起CT气室闪络击穿.     

Reduced purine catabolite production in the postischemic rat heart: a31P NMR assessment of cytosolic metabolites

Ischemia can cause release of adenosine and purine catabolites from the heart, through the breakdown of ATP. If repeated periods of ischemia are induced, the efflux of purines is markedly reduced, although it is not clear if this is beneficial for the long-term survival of the heart. We have investigated changes in high-energy phosphates and purine release in the isolated perfused rat heart using³¹P NMR spectroscopy and high-performance liquid chromatography. Hearts were subjected to one of the following protocols: Group A—1 min of total global ischemia (TGI) after 40 min, 60 min, and 85 min of perfusion (a total of 3 × 1 min ischemia); Group B—1 min of TGI after 40 min of perfusion, 10 min of TGI after 50 min of perfusion, and a final 1 min of TGI after 85 min of perfusion. The profile of high-energy phosphate metabolites, P_i accumulation and purine release was similar for each 1-min period of TGI in Group A, whereas phosphocreatine content was increased and ATP content reduced by an extended period of TGI in Group B, leading to a less severe acidosis and purine efflux in the final 1 min of TGI at 85 min of perfusion. In conclusion, the reduced purine release observed in Group B may be related to the preischemic ATP pool size and accessibility and the increased myocardial energy reserve in the form of phosphocreatine.     

In vivo1H MR spectra analysis by means of second derivative method

Short echo time (TE) in vivo PRESS¹H MR spectra (2 T. TE = 35 ms) of normal brain were fitted in the frequency domain using the second derivative method. In this approach, local maxima and hidden peaks are found as local minima of spectrum second derivative. The Lorentzian robust minimisation procedure (referred to as maximum likelihood or m-estimate fitting) using Levenburg -Marquardt non-linear fitting engine was applied. Spectral lines were approximated under the assumption of the mixed Lorentzian/Gaussian lineshapes. The same procedure was applied to 18 proton spectra. The number of peaks found within the range of 0.74/4.2 parts per million (ppm) was 52 ± 3 and their positions were almost the same. The fitted lines were assigned on the basis of the J-pattern recalculated for the field strength of 2 T and by comparing the chemical shifts with the shifts in the single compound spectra. The ratios of main metabolites, such as NAA/Cr, Cho/Cr, Cho/NAA and ml/Cr, are in accord with those obtained earlier using the software supplied with the MR imager and the absolute concentrations ofN-acetylaspartate (NAA). choline containing compounds (Cho),myo Inositol (ml), glucose (Gle) and glutamate (Glu) obtained from the fit agree with those reported in literature, which confirms the usefulness of the second derivative method in routine analyses of¹H MR brain spectra.     

Comparison of in vivo1H MRS of human brain tumours with1H HR-MAS spectroscopy of intact biopsy samples in vitro

High resolution magic angle spinning (MAS)¹H nuclear magnetic resonance (NMR) spectroscopy has been employed to study intact human brain tumour tissue and comparison with the corresponding in vivo spectrum has been made. Two dimensional¹H MAS-NMR measurements, including J-resolved and homonuclear shift correlation spectra, were obtained to aid metabolite signal assignment. MAS gave greatly improved line-shape and reduced line-width in comparison to conventional high resolution in vivo¹H MRS of intact tissue, permitting the simultaneous detection of cellular lipids and metabolites. The technique provides the most direct method for comparison of in vivo spectra with high resolution spectra in vitro and hence allows more reliable peak assignment of in vivo¹H MRS spectra.     

Changes in proton transverse relaxation times of rat myocardium that has suffered a previous oxidative insult

An oxidative insult can induce severe damage, as in the phenomenon of myocardial ischemia and reperfusion. However, there are situations in which the damage is not so obvious (e.g., silent ischemia or aging), and the negative effects will be seen only in time. Our aim was to reveal these small changes in the myofilaments by using the nuclear magnetic resonance (NMR) technique. We used Wistar rat hearts in a constant-pressure Langendorff system, perfused with oxygenated Krebs-Henseleit buffer at 37°C. After 15 minutes of stabilization, the hearts were perfused with buffer supplemented with H₂O₂ at 50, 75, or 100 μmol/L for 15 or 30 minutes. Fifteen-minute and 45-minute perfusion controls and unperfused hearts were also collected. Heart rate (HR) and left ventricular developed pressure (LVDP) were determined with the help of a latex balloon, inserted in the left ventricle and connected with a pressure transducer. Proton transverse relaxation times (T ₂) were determined at the end of the experiment.T ₂ values were measured again in the same tissue fragments after they had been glycerinated and incubated in relaxation and rigor media. The functional parameters (HR, LVDP, coronary flow) were not significantly changed in control and 50 μmol/L H₂O₂ groups but were increased in the 75 μmol/L H₂O₂ group and significantly decreased in the 100 μmol/L H₂O₂ group.T ₂ is significantly decreased in rigor media starting with 50 μmol/L H₂O₂ administrated for 30 minutes and does not correlate with dose and duration of the oxidative insult.T ₂ in rigor is shorter than in relaxation media within the groups, and this difference is increased in the treated hearts.     

Physiological constraints on changes in pH and phosphorus metabolite concentrations in ischemically exercising muscle: implications for metabolic control and for the interpretation of31P-magnetic resonance spectroscopic studies

Relationships between pH and the concentrations of phosphocreatine (PCr), inorganic phosphate (Pi), and lactate during ischemic exercise depend on passive buffering, proton consumption as a consequence of net PCr breakdown, the control of glycogenolysis, (particularly in relation to the concentration of Pi, a substrate of glycogen phosphorylase that is produced by net PCr breakdown), and the creatine kinase equilibrium. The author analyzes the implications of these relationships for the interpretation of³¹P-magnetic resonance spectroscopic data and for the control of glycogenolysis. For realistic adenosine diphosphate (ADP) concentrations, given the constraints of the creatine kinase equilibrium, the pH must be near-linear with lactate, with an apparent buffer capacity (i.e., the ratio of lactate accumulation to pH change) that is nearly twice the true buffer capacity (i.e., the ratio of net proton loading to pH change). The implications for glycogenolytic control depend on adenosine triphosphate (ATP) turnover, but an upper limit of activation of glycogen phosphorylase (i.e., the amount of thea form) that would permit no increase in ADP concentration can be calculated. Phosphorylase activation during ischemic exercise seems approximately proportional to the power output, consistent with calcium stimulation of phosphorylaseb kinase. In simulations, ADP concentration is highly sensitive to this proportionality, as (unlike in purely oxidative exercise) ADP concentration is not known to participate in any closed feedback loops in ischemic exercise.     

Predication of Thermal Conductivity of Mg2X (X = Ge and Sn) by Molecular Dynamics

Molecular dynamics (MD) simulations of elastic and thermal properties of Mg₂X (X = Ge and Sn) based on anti-fluorite structure (CaF₂) at temperature range 300?700 K were presented. The MD simulation in this study involving the Morse?type potential functions, and the Busing–Ida potential to determine the interatomic interaction among cluster atoms size 4×4×4 unit cells of 768 atoms {512?Mg^1.2+, 256?(Ge, Sn)^2.4?}. The potential parameter functions of the cluster atoms were indicated by random numerical method and fit lattice parameter from the experimental data obtained at room temperature. The calculation of lattice parameter, pressure, temperature and energy contributes to evaluation of the elastic properties. The results showed that Mg₂Ge had better elasticity than Mg₂Sn. On the other hand, Mg₂Sn had less thermal conductivity than Mg₂Ge. Since thermal conductivity decreases with increasing temperature, the interesting feature of thermal conductivity is particulary useful to enhance thermoelectric performance of materials.     

Tissue oxygen tension measurements in the Shionogi model of prostate cancer using 19 F MRS and MRI

Objectives: To investigate changes in tumour tissue oxygenation throughout the tumour growth–regression–relapse cycle in an androgen-dependent animal tumour model. Materials and methods: ¹⁹F T₁ relaxometry of Perfluoro-15-Crown-5-Ether was used to measure in vivo partial oxygen pressure (pO₂) of Shionogi tumours on a 2.35-T MR scanner. Perfluoro-15-Crown-5-Ether was administered as an emulsion injected intravenously or as a neat compound injected directly into the tumour. Non-localized, tumour ¹⁹F T₁ measurements, made at multiple time points throughout the tumour cycle, were translated into pO₂ levels. Results: No correlation between tumour size and pO₂ values was found. Values of pO₂ for growing tumours (50 ± 30 torr) were significantly lower than for regressing and relapsing tumours after 9 days post-castration (70 ± 10 torr, p<0.05). Maximum pO₂ values (90 ± 30 torr) were reached between fifth and eighth day post-castration, when tumour pO₂ was significantly higher than both pre-castration (p<0.001) and after 9 days post-castration (p<0.05). Conclusion: We demonstrate that longitudinal pO₂ measurements in vivo are feasible. Values of pO₂ for growing androgen-dependent tumours were significantly lower than for regressing and relapsing androgen-independent tumours. These results have potential clinical importance in optimizing the timing of chemotherapy and/or radiotherapy of hormone dependent tumours.     

Comparative Characteristics of Na0.5K0.5NbO3 Films on Pt by Pulsed Laser Deposition and Magnetron Sputtering

Ferroelectric Na_0.5K_0.5NbO₃ (NKN) thin films were grown on the Pt₈₀Ir₂₀ polycrystalline substrates by pulsed laser deposition (PLD) and radio frequency-magnetron sputtering (RF) technique using the same stoichiometric Na_0.5K_0.5NbO₃ ceramic target. X-ray diffraction proved both PLD- and RF-made Na_0.5K_0.5NbO₃/Pt₈₀Ir₂₀ films are single phase and have preferential c-axis orientation. Temperature dependence of dielectric permittivity reveals the presence of two phase transitions around 210 and 410°C. Capacitance vs. applied voltage C-V @ 100 kHz, I-V, and P-E hysteresis characteristics recorded for the vertical capacitive structures yielded loss tanδ = 0.026 and 0.016, tunability about 44.5 and 30% @ 100 kV/cm, Ohmic resistivity 6.7 × 10¹² Ω·cm and 0.2 × 10¹² Ω·cm, remnant polarization 11.7 and 9.7 μC/cm², coercive field 28.0 and 94.6 kV/cm for PLD- and RF-films, respectively. Piezoelectric test carried out in hydrostatic conditions showed piezoelectric coefficient d _H = 21 for PLD-NKN and 15 pC/N for RF-NKN film.     

The magnitude of signal errors introduced by ISIS in quantitative31P MRS

It is well known that the quality of a quantitative³¹P MRS measurement relies largely on the performance of the volume selection method, and that image selected in vivo spectroscopy (ISIS) suffers from contaminating signal caused mostly by Tl smearing. However, these signal errors and their magnitude are seldom addressed in clinical studies. The aim of this study was therefore to investigate the magnitude of signal errors in³¹P MRS when using ISIS. The results from the measurements with a homogeneous head phantom are as follows: at low TR/T1 ratios the contamination increases rapidly, especially for small (< 27 cm³) VOI sizes; at TR/T1 = 1, the signal from a 27 cm³ VOI was 20% too high, and from an 8 cm³ VOI 150% too high. The signal obtained from different VOI positions varied between 80 and 127%. The signal varied linearly with the³¹P concentration in the object. However, a too high signal was obtained when the concentration was lower in the region of interest (inner container) than in the rest of the phantom. The agreement between the simulations and measurements shows that the results of this study are generally applicable to the measurement geometry and the ISIS experiment order rather than being specific for the MR system studied. The errors obtained both experimentally and in computer simulations are too large to be ignored in clinical studies using the ISIS pulse sequence.     

Mechanisms of31P relaxation in phosphorus metabolites

Measurements have been made of the longitudinal relaxation timeT ₁ of³¹P for the individual resonances of the metabolites AMP, ADP, ATP, P_ir and PCr (phosphocreatine) in H₂O and D₂O solutions from 5 to 60°C at various concentrations and at frequencies of 40 MHz (2.3 T) and 120 MHz (7 T). The contributions of dipolar, chemical shift anisotropy, and spin-rotation mechanisms have been separated, and activation parameters of the underlying molecular reorientations have been determined.     

Investigation of multidrug resistance in cultured human renal cell carcinoma cells by 31P-NMR spectroscopy and treatment survival assays

KTCTL-26 and KTCTL-2 are renal cell carcinoma (RCC) lines with high and lowexpression of P-170 glycoprotein, respectively. Inherent differences between the two cell lines in terms of phosphate metabolites and growth characteristics in culture were examined for possible association with multidrug resistance (MDR). Differences in response to drug treatment were investigated for 40 h incubations with various doses of vinblastine (VBL) alone or as cotreatments with various concentrations of the calcium antagonist diltiazem (DIL) and/or interferon–α (IFN-α). Treatment effects were quantitated using the MTT survival assay and ³¹P magnetic resonance spectroscopy (MRS) to determine phosphate metabolite profiles in intact cells. KTCTL-2 and KTCTL-26 cells exhibited significant inherent differences in phosphocholine, glycerophosphocholine, glycerophosphoethanolamine, and phosphocreatine levels. KTCTL-26 cells were more sensitive than KTCTL-2 to 0.011μM VBL alone (87% vs. 102% survival) or to 0.011μM BL + 10μM DIL (55% vs. 80% survival). The latter treatment resulted in a significant decrease in the ratio of phosphocholine to glycerophosphocholine in KTCTL-26 cells but no significant changes in phosphate metabolites in KTCTL-2 cells. Metabolomic ³¹P MRS detects different metabolite profiles for RCC cell lines with different MDR phenotypes and may be useful for noninvasive characterization of tumors in a clinical setting.This revised version was published online in August 2005 with a corrected sequence of authors.     

Ultra-fast three dimensional imaging of hyperpolarized 13C in vivo

Objective: PASADENA, a chemical method of enhancing nuclear spin polarization has demonstrated ¹³C polarizations of order unity for the nascent products of molecular addition by parahydrogen. The extreme brevity of signal enhancement obtained by hyperpolarization requires improved ¹³C MR in vivo imaging techniques for their optimum utility. Materials and Methods: ¹³C imaging sequences, including ¹³C 3D FIESTA, were compiled for a GE LX 1.5 T clinical MR scanner. Two water soluble ¹³C imaging agents were hyperpolarized utilizing parahydrogen and an automated polarizer. ¹³C polarization was quantified in flow phantoms and in rats with jugular vein catheters. Results: Fast 3D FIESTA ¹³C MR imaging technique acquired sequential 3D images (3.66 s/acquisition) with superior SNR. Hyperpolarized ¹³C solutions and vascular phantoms achieved a maximum signal of 26,624±593. In vivo ¹³C MR images of the cardiopulmonary circulation showed maximum ¹³C signal of 2,402±158. ¹³C images acquired within 3.66 s showed signal enhancement over 10,000 compared to equilibrium polarization. Conclusion: 3D-FIESTA was effective for sub-second in vivo imaging of hyperpolarized ¹³C reagents produced in a custom-built parahydrogen polarizer. Application to ¹³C hyperpolarized by parahydrogen is demonstrated in vitro and in vivo     

Transmit/receive headcoil for optimal <Superscript>1</Superscript>H MR spectroscopy of the brain in paediatric patients at 3 T

¹H magnetic resonance (MR) spectroscopy is a useful tool to obtain metabolic information from the brain in paediatric patients. To detect signals of metabolites at low concentrations or from small volumes, the signal-to-noise ratio (SNR) has to be optimized. The SNR can be increased by going to higher field strengths. However, this leads to higher spectral bandwidths, which increases the chemical shift artefact. Here we present a transmit/receive headcoil which is adapted to the dimensions of the paediatric head and enables PRESS localization with high radio-frequency (RF) bandwidths that minimize the chemical shift displacement to only 5%. In addition, since the pulse lengths are shorter with higher RF bandwidths, the echo time can be reduced to 10 ms improving SNR as well.Parts of this work have been presented at the European Society for Magnetic Resonance in Medicine and Biology in Rotterdam in 2003