Function Of Sodium Concentration Research Articles

A dual-tuned multichannel bilateral RF coil for 1 H/23 Na breast MRI at 7 T.

Sodium MRI has shown promise for monitoring neoadjuvant chemotherapy response in breast cancer. The purpose of this work was to build a dual-tuned bilateral proton/sodium breast coil for 7T MRI that provides sufficient SNR to enable sodium breast imaging in less than 10 minutes. The proton/sodium coil consists of 2 shielded unilateral units: 1 for each breast. Each unit consists of 3 nested layers: (1) a 3-loop solenoid for sodium excitation, (2) a 3-loop solenoid for proton excitation and signal reception, and (3) a 4-channel receive array for sodium signal reception. Benchmark measurements were performed in phantoms with and without the sodium receive array insert. In vivo images were acquired on a healthy volunteer. The sodium receive array boosted 1.5 to 3 times the SNR compared with the solenoid. Proton SNR loss due to residual interaction with the sodium array was less than 10%. The coil enabled sodium imaging in vivo with 2.8-mm isotropic nominal resolution (~5-mm real resolution) in 9:36 minutes. The coil design that we propose addresses challenges associated with sodium's low SNR from a hardware perspective and offers the opportunity to investigate noninvasively breast tumor metabolism as a function of sodium concentration in patients undergoing neoadjuvant chemotherapy.

Sodium intercalation/de-intercalation mechanism in Na4MnV(PO4)3 cathode materials

Na4MnV(PO4)3 is a sodium ion conducting material with a NASICON type crystal structure. This phase is not much known as an electrode material. The present work focuses on the sodium ion intercalation/de-intercalation mechanism and charge/discharge behavior of the material. The Na4MnV(PO4)3 is synthesized through a sol-gel process and characterized by XRD, SEM, and XPS. The structural analysis confirms the formation of a phase pure crystalline material with nanometric particle size which adopts a trigonal crystal structure. Galvanostatic intermittent titration technique (GITT) measurements indicate that Na4MnV(PO4)3 is electrochemically active having slanting voltage plateaus. Ex-situ and In-situ XRD analysis, as a function of sodium concentration, indicate that the intercalation/de-intercalation of sodium is associated with a single-phase reaction rather than a biphasic reaction when cycled between 1.5 and 4.5 V. The electrochemical measurements on composite electrodes, Na4MnV(PO4)3/CNTS (1 & 3 wt.%), show promising charge/discharge capacity (∼140 mAh/g), good cyclability (100% capacity retention after 40 cycles) and reasonable rate capability. The cyclic voltammetry (CV) and X-ray Photoelectron Spectroscopy (XPS) analyses indicate that the main contributions towards the activity of Na4MnV(PO4)3 can be attributed to the active of Mn2+/Mn3+ and V3+/V4+ redox couple with partial activity of V4+/V5+. The obtained results suggest that Na4MnV(PO4)3 is a promising electrode material which can be achieved better rate performance with long cycling stability and battery performance through engineering of the particle morphology and microstructure.

Determination of residual sodium content in silver and silver oxide composite materials

This paper deals with a procedure to determine the residual sodium content in silver oxide-metal oxide (intermediary product) and silver-metal oxide composites. In addition, an equilibrium curve showing the evolution of sodium content in the intermediary product as a function of sodium concentration in the washing liquid is given. So the residual sodium content in the solid may be subsequently deduced by measurement of the sodium concentration in the corresponding washing liquid. The influence of both silver and sodium contents on the procedure is also investigated.

Thrombin inhibitor design: X-ray and solution studies provide a novel P1 determinant.

The crystal structures of proflavin and 6-fluorotryptamine thrombin have been completed showing binding of both ligands at the active site S1 pocket. The structure of proflavin:thrombin was confirmatory, while the structure of 6-fluorotryptamine indicated a novel binding mode at the thrombin active site. Furthermore, speculation that the sodium atom identified in an extended solvent channel beneath the S pocket may play a role in binding of these ligands was investigated by direct proflavin titrations as well as chromogenic activity measurements as a function of sodium concentration at constant ionic strength. These results suggested a linkage between the sodium site and the S1 pocket. This observation could be due to a simple ionic interaction between Asp189 and the sodium ion or a more complicated structural rearrangement of the thrombin S1 pocket. Finally, the unique binding mode of 6-fluorotryptamine provides ideas toward the design of a neutrally charged thrombin inhibitor.

Enhanced protein kinase C mediated inhibition of renal dopamine synthesis during high sodium intake

The synthesis of dopamine, from l-β-3,4-dihydroxyphenylalanine ( l-DOPA), in renal tissue of rats on either a normal sodium (NS) or high sodium (HS) diet for 1 week or 6 weeks was examined. Aromatic l-amino arid decarboxylase (AAAD) activity determined in kidney homogenates in “1 week HS” ( V max = 11.5 ± 1.6 nmol/mg protein/hr) and “6 weeks HS” rats ( V max = 10.6 ± 1.5 nmol/mgprotein/hr) was greater (P < 0.02) than that in “NS” rats ( V max = 7.7 ± 0.8 nmol/mg protein/hr). K m (μM) values in “NS”, in “1 week HS” and “6 weeks HS” rats were similar. The formation of dopamine in kidney slices loaded with 100 μM l-dopa depended exponentially on the concentration of sodium in the medium (0–160 mM). In kidney slices obtained from “1 week HS” rats the decarboxylation of added l-dopa was significantly greater (P < 0.01) than that observed in kidney slices obtained from “NS” and “6 weeks HS” rats; the rate constant of formation of dopamine as a function of sodium concentration in the incubation medium was, however, similar in “NS” rats to that in “1 week HS” and “6 weeks HS” rats. Ouabain produced a concentration dependent decrease in the synthesis of dopamine in all three experimental groups; the magnitude of the inhibitory effect of 1.0 mM ouabain was greater in “1 week HS” rats (77% reduction; P < 0.01) than in “NS” rats (59% reduction; P < 0.01) and in “6 weeks HS” rats (23% reduction; P = 0.08). Activation of protein kinase C by phorbol 12,13-dibutyrate (PDBu) and the calcium ionophore A23187 produced a concentration-dependent reduction in the formation of dopamine in rat kidney slices, but not in kidney homogenates; the magnitude of the inhibitory effect was greater in “1 week HS” rats than in “NS” and “6 weeks HS” rats. Submaximal concentrations of PDBu (10 nM) were synergistic with the inhibitory effect of A23187 on the formation of dopamine: again, this effect was more marked in “1 week HS” rats than in “NS” and “6 weeks HS” rats. The effects of PDBu and PDBu plus A23187, but not those of A23187 alone, were antagonized in a concentration-dependent manner by d-sphingosine, a protein kinase C inhibitor. It is concluded that the increased activity of AAAD in renal tissues of rats submitted to HS intake is accompanied in “1 week HS” but not in “6 weeks HS” rats by enhanced inhibition of dopamine formation during protein kinase C activation.

The α-2 isomer of the sodium pump is inhibited by calcium at physiological levels

The inhibition of the (Na,K)ATPase by calcium was investigated in plasma membrane preparations of rat axolemma, skeletal muscle and kidney outer medulla. Ouabain titration curves demonstrated that physiological calcium (0.08-5 microM) inhibited mainly the high affinity alpha 2 isomer. In axolemma all the (Na,K)ATPase had high ouabain affinity and calcium inhibited 40-50% of the activity with a Ki of 1.9 +/- 0.9 x 10(-7) M. In skeletal muscle high and low ouabain affinity components were present in equal amounts and calcium inhibited only the high affinity component with a Ki of 1.3 +/- 0.3 x 10(-7) M. Kidney enzyme had a low affinity for ouabain and showed very little sensitivity to calcium in the physiological range. It was demonstrated that high calcium levels inhibit the enzyme in a general sense, irrespective of the isomer, with a Ki of 6.5 +/- 6 x 10(-4) M for the kidney and 5.9 +/- 4 x 10(-4) M for the axolemma enzymes. In axolemma, enzyme activity was studied as a function of sodium concentration. Physiological calcium reduced Vmax while not significantly changing K 0.5 for sodium binding.

Thermodynamic properties of iron doped beta?-alumina by e.m.f. measurements with beta-alumina electrolytes

Thermodynamic studies of the non-stoichiometric iron doped beta″-alumina (IDβ″) phase were carried out by electrochemical measurements coupled with coulometric titration using the cell Naliq/Liβ″-alumina/IDβ″. Hot pressing and glass sealing techniques were developed and employed to obtain a suitable and stable Liβ″-alumina/IDβ″ interface. The equilibrium e.m.f. of the cell was determined as a function of sodium concentration over the temperature range 444 to 523 K. The range of sodium concentrations over which the IDβ″ phase is stable was also determined. The relative partial molar thermodynamic quantities of sodium,\(\overline {\Delta G} _{Na} \),\(\overline {\Delta H} _{Na} \), and\(\overline {\Delta S} _{Na} \) in IDβ″ alumina as a function of sodium concentration were obtained from cell e.m.f. data.

Exploration of apical sodium transport mechanisms in an epithelial model by network thermodynamic simulation of the effect of mucosal sodium depletion: II. An apical sodium channel and amiloride blocking

This paper is the second part of a modeling study on apical sodium transport mechanisms in tight epithelia. In the first part (this issue) we explored three expressions for the apical membrane sodium permeability (PapNa) and showed that only a PapNa which varies as a function of sodium concentration allows simulation of the well known saturation of the short-circuit current with increasing mucosal sodium concentration. However, the ad hoc expressions used have no mechanistic interpretation. We show here that if, instead of an ad hoc expression, one includes a one-site, two-barrier sodium channel in the apical membrane, the model also simulates this saturation. In addition, the equivalent apical sodium permeability computed from the simulations appears to be very similar to the phenomenological equation used by Fuchs et al. (1977) to fit the decrease of the apical sodium permeability with increasing mucosal sodium. The apical sodium channel simulated here is thus a possible mechanism for the feedback effect of the mucosal and intracellular sodium concentrations on the apical sodium permeability. This channel also allows the simulation of the competitive inhibition of the sodium current by amiloride, and the concomitant inhibition of the apical sodium permeability.

Development of Fluctuation Monitor Type Sodium Ionization Detector

In order to improve the sensitivity and the reliability of the sodium leak detection system used in the fast breeder reactors, a new type SID (sodium ionization detector) has been developed, in which the monitored signal is only the fluctuating component of the current between the filament and the ion collector. The fluctuating component was extracted by a band pass filter and its root mean square value was calculated as the SID signal. Fluctuation characteristics of the output current were studied by its frequency spectrum. The results revealed that the current spectrum was affected by the particle size distribution of the aerosol and was most clearly distinguished from that of the background current in the frequency region of 0.5–10 Hz. Output characteristics of the fluctuation monitor type SID (FM-SID) were obtained as a function of sodium concentration in the gas. The FM-SID sensitivity was lowered by impurities in the gas, such as oxygen and water vapor. Finally, in comparisons with the conventional DC-SIDs, the background noise level of the FM-SID was much lower and SIN ratio was greatly improved. The detectable sodium concentration level was ten times lower than that of the DC-SID.

Development of fluctuation monitor type sodium ionization detector.

In order to improve the sensitivity and the reliability of the sodium leak detection system used in the fast breeder reactors, a new type SID (sodium ionization detector) has been developed, in which the monitored signal is only the fluctuating component of the current between the filament and the ion collector. The fluctuating component was extracted by a band pass filter and its root mean square value was calculated as the SID signal. Fluctuation characteristics of the output current were studied by its frequency spectrum. The results revealed that the current spectrum was affected by the particle size distribution of the aerosol and was most clearly distinguished from that of the background current in the frequency region of 0.5–10 Hz. Output characteristics of the fluctuation monitor type SID (FM-SID) were obtained as a function of sodium concentration in the gas. The FM-SID sensitivity was lowered by impurities in the gas, such as oxygen and water vapor. Finally, in comparisons with the conventional ...

Na+-coupled glycine transport in reticulocyte vesicles of distinct sidedness: stoichiometry and symmetry.

Sodium-coupled glycine transport has been studied using membrane vesicles of distinct sidedness, either inside-out or right side-out, prepared from sheep reticulocytes. The activity is chloride dependent and characterized by high and low apparent affinities for glycine (K'm approximately equal to 0.5 mM and greater than 10 mM) for both types of vesicles as well as intact cells. Transport is symmetrical with respect to similar apparent affinity constants for glycine, for both the high- and low-affinity systems, and for sodium. Direct measurements of the sodium/glycine coupling indicate a ratio of 2:1, consistent with kinetic data fitted to a Hill-type equation describing glycine flux as a function of sodium concentration.

Transient capacitance spectroscopy of Na+-induced surface states at the Si/SiO2 interface

The interface states induced by the drift of Na+ ions to the Si/SiO2 interface are investigated in metal-oxide-semiconductor capacitors made on n-type Si using deep level transient spectroscopy. The results clearly reveal the existence of two types of defects. The dominant ones yield an increase in the density of states mainly near the Si conduction band, resulting in a band tail. These states can be annealed out by pumping of the Na+ ions back to the metal gate. The introduction kinetics of these traps as a function of sodium concentration at the Si/SiO2 interface ([Na+]) exhibits a strong increase near [Na+]∼3×1012 ions/cm2. The other type of defect, created in less significant amounts, accounts for a flat continuum of levels throughout the Si band gap. These traps are little affected by the Na+ ions leaving the Si surface, which is indicative of a more or less irreversible degradation of the Si/SiO2 interface. These results are compared with other authors’ experimental data and are discussed in terms of several possible physical models.

Na+-dependent hexose transport in vesicles from cultured renal epithelial cell line.

Apical membrane vesicles were prepared from cultured epithelia formed by LLC-PK1 cells using a calcium precipitation technique. alpha-Methylglucoside uptake into this vesicle preparation was markedly stimulated by sodium and inhibited by phlorizin. In addition, a transient "overshoot" of intravesicular alpha-methylglucoside concentration above its equilibrium value was observed under initial sodium gradient conditions. The specificity of this sodium-dependent hexose transporter closely resembled that found in the mammalian kidney brush border membrane, e.g., alpha-methylglucoside, D-glucose, and D-galactose apparently share the transporter while 2-deoxy-D-glucose, mannose, and fructose do not. Kinetic analysis of the sodium-dependent component of alpha-methylglucoside flux into LLC-PK1 apical membrane vesicles indicates the existence of single transporter with Km congruent to 2 mM and Vmax congruent to 3 nmol.min-1.mg protein-1. Measurement of alpha-methylglucoside uptake as a function of sodium concentration is consistent with a sodium:sugar stoichiometry of approximately 2:1.l There is a good correlation over time between the development of the concentrating capacity of the intact epithelium for alpha-methylglucoside and the transport properties of the vesicle preparation.

Reversibility of sodium-induced aggregation of sonicated phosphatidylserine vesicles.

The kinetics of sodium-induced aggregation of sonicated phosphatidylserine vesicles has been studied as a function of sodium concentration and temperature. The concentration threshold for aggregation induced by monovalent sodium has been found to be 550 mM sodium by stopped-flow rapid-mixing techniques. This aggregation is completely reversible to changes in sodium ion concentration and to changes in temperature. The aggregation rate decreases with increasing temperature, indicating that the backward reaction rate increases more rapidly with temperature than does the forward rate.

Optical properties of the sodium-tungsten bronzes and tungsten trioxide

A polarization-modulation ellipsometric technique was used to make direct measurements of the optical dielectric constants of single-crystal specimens of the nonstoichiometric tungsten-bronze compound ${\mathrm{Na}}_{x}\mathrm{W}{\mathrm{O}}_{3}$ ($0.52lxl0.94$) and W${\mathrm{O}}_{3}$, in the energy range from 1.0 to 5.5 eV. A method for determining the optical constants of anisotropic materials from modulation ellipsometry was developed in the study of tungsten trioxide. The behavior of the sodium bronzes as a function of sodium concentration is in agreement with recent calculations of the band structures for these materials. The system exhibits almost rigid-band behavior. The data were fit to the classical Drude free-electron model for the optical properties of metals. The W${\mathrm{O}}_{3}$ dielectric constants were used to directly determine the contribution of higher-energy bound-electron transitions to the optical constants of ${\mathrm{Na}}_{x}\mathrm{W}{\mathrm{O}}_{3}$ in the free-electron region. The results of jointdensity-of-states calculations were used in conjunction with the free-electron model to demonstrate that a relatively large discrepancy between conduction-electron relaxation times derived from the free-electron model alone and those determined from the dc conductivity may result, in part, from underlying interband transitions.

Vapor-deposited metal-gas alloys of sodium and ammonia

Films of sodium and ammonia were formed directly from vapor onto substrates held at or below 5 K. The electrical resistivity of the films was measured as a function of sodium concentration. A metal-nonmetal transition as a function of composition was observed at concentrations in the 45–50 mole % range. The transition was found to be anomalous in that the resistivity was not a monotonic function of the sodium concentration. The data indicate that there is enhanced conductivity over a narrow concentration range on the nonmetal side of the transition. The conductivity is not magnetic field dependent up to the maximum available field of 4 kOe. No evidence was found for the anomalous electrical conductivity previously reported for bulk, dilute sodium-ammonia solids that were quick-frozen from liquid solutions.

The influence of ouabain on in vitro renin secretion.

SummaryUsing rat kidney cortex slices, in vitro renin secretion was measured as a function of sodium concentration of the incubation medium. We found, as have many others previously, that renin secretion increases with increasing medium sodium concentration. However, in the presence of 10−3M ouabain, renin secretion decreased with increasing medium sodium concentration. Since others have shown that intracellular sodium concentration varies directly with medium sodium concentration in the presence of ouabain, it seems unlikely that these results can be explained by a single unifying hypothesis, such as that renin secretion is inversely related to intracellular sodium concentration.

The interrelationships between sodium ion, calcium transport and oxygen utilization in the isolated chick chorioallantoic membrane

The interrelationships between sodium ion, calcium transport and oxygen utilization have been investigated in the chick chorioallantoic membrane. The oxygen uptakes of the two surface layers of the tissue, the ectoderm and the endoderm, were separated into their basal, Na(+) dependent and Ca(++) dependent components. The endoderm has a basal rate of respiration of 3.6 μliters O2/cm(2)/hr and a Na(+) dependent component of 1.4 μliters O2/cm(2)/hr. The ectoderm has a basal rate of respiration of about 3.5 μliters O2/cm(2)/hr, and Na(+) and Ca(++) dependent components of 1.1 and 3.6 μliters O2/cm(2)/hr, respectively. The rate of ectodermal calcium transport and calcium-stimulated oxygen uptake is strictly dependent on the presence of sodium in the bathing medium, and complex kinetics are observed as a function of sodium concentration. On the other hand, in 140MM Na(+) the rate of calcium transport exhibits simple saturation kinetics as a function of calcium concentration. Ca(++)/O2 ratios determined for many different rates of transport give a ratio of about 0.5, a value much lower than similar ratios determined for other transport mechanisms. The calcium transport mechanism in the ectoderm responds to changes in transport rate very sluggishly, taking 30 to 50 min to give a maximum response. The differences between the calcium transport mechanism in this membrane and other known transport systems are discussed and it is suggested that these differences may represent the adaptations necessary for transcellular calcium transport.

Effects of tonicity and glucose on intestinal sodium and water absorption in the rat.

The rat small intestine was perfused in vivo with solutions of varying sodium concentrations. Some solutions were hypotonic, glucose or mannitol was added to others to make them isosmotic. Sodium absorption was a function of sodium concentration from both isosmotic and hypotonic solutions. The increased water absorption from a slightly hypotonic solution was associated with increased sodium absorption. With a markedly hypotonic solution, net sodium entry into the lumen and decreased water absorption suggested disruption of membrane integrity. Glucose absorption was associated with increased sodium and water absorption. The increase in sodium absorption was greater than predicted from solvent drag by the volume of water associated with absorption of the glucose in isosmotic solution. Sodium influx was also increased in the glucose solution, indicating a relation between glucose absorption and sodium transport. All glucose effects were abolished by phlorizin.

Interpretation of hexose-dependent electrical potential differences in small intestine.

ACTIVELY transported sugars added to the solution bathing the mucosal surface of the small intestine produce an increase in the electrical potential difference (p.d.) and short-circuit current (Isc) across the tissue1–4. Schultz and Zalusky1 have shown that the increase in the Isc (ΔIsc) across rabbit ileum is a function of both sugar and sodium concentrations in the bathing solution. When sodium was replaced with potassium, the maximum ΔIsc caused by addition of sugars was a linear function of sodium concentration. Recently, Barry et al.5 reported that the increase in the p.d. (Δp.d.) following addition of galactose to the mucosal bathing solution of everted sacs of rat mid-intestine is independent of sodium concentration when mannitol is used to replace sodium chloride, but is approximately a linear function of sodium concentration when potassium is used to replace sodium. They have concluded that the “galactose dependent potential is unaffected by sodium concentration but is reduced by increasing potassium concentration”. Lyon and Crane6 have reported that, in rat jejunum, the maximum Δp.d. resulting from addition of actively transported sugars is independent of sodium concentration when tris [2-amino-2(hydroxymethyl)-1,3-propanediol] is used to replace sodium, but decreases when potassium is used as replacement ion.