THE CONTROL OF THE MEMBRANE POTENTIAL OF MUSCLE FIBERS BY THE SODIUM PUMP

Frog sartorius muscles were made Na-rich by immersion in K-free sulfate Ringer's solution in the cold. The muscles were then loaded with Na²⁴ and the extracellular space cleared of radioactivity. When such Na-rich muscles were transferred to lithium sulfate Ringer's solution at 20°C, Na efflux was observed to increase with time, to reach a maximum about 15 minutes after the transfer of the muscles to Li₂SO₄, and then to decline. The decline in efflux from these muscles was proportional to ([Na]_i)⁸ over a considerable range of [Na]_i. The membrane potential of Na-rich muscles was about -48 mv in K-free sulfate Ringer's at 4°C but changed to -76 mv in the same solution at 20°C and to -98 mv in Li₂SO₄ Ringer's at 20°C. By contrast, muscles with a normal [Na]_i showed a fall in membrane potential when transferred from K-free sulfate Ringer's to Li₂SO₄ Ringer's solution. The general conclusions from this study are (a) that Na extrusion is capable of generating an electrical potential, and (b) that increases in [Na]_i lead to reversible increases in P_Na of muscle fibers.

Characterisation of sodium cations in dehydrated zeolite NaX by 23Na NMR spectroscopy

23Na MAS, 2D nutation MAS, and DOR NMR spectroscopy has been applied to characterise the location of sodium cations in dehydrated zeolite NaX (Si/Al = 1.23). The 23Na MAS NMR spectra recorded at three different magnetic field strengths were decomposed by computer simulation into five lines, which were attributed to five crystallographically distinct cation sites known from X-ray diffraction studies. The assignments of the lines follow from electric field gradient calculations at the 23Na nuclei applying a simple point charge model based on crystal structure data. A weak Gaussian line at low field (delta iso = -6 ppm) is assigned to sodium cations at site I, two broad quadrupole patterns at the high-field side of the spectra are attributed to site I' (delta iso = -19 ppm, QCC = 5.2 MHz, eta = 0) and site II cations (delta iso = -15 ppm, QCC = 4.6 MHz, eta = 0), and two quadrupolar lines dominating the central region of the spectra originate from Na+ at two different III' sites (delta iso = -13 and -29 ppm, QCC = 2.6 and 1.6 MHz, eta = 0.7 and 0.9, respectively). Na+ ions located on a second I' site could be identified from the DOR NMR spectra. The line assignment is further corroborated by the reasonable agreement of the site occupancies estimated from the line intensities with those determined by X-ray diffraction. In addition, sodium site populations of five dehydrated zeolites NaX and NaY with Si/Al ratios between 1.09 and 4.0 were derived from the 23Na MAS NMR spectra.

Postictal alteration of sodium content and apparent diffusion coefficient in epileptic rat brain induced by kainic acid

PURPOSE

We studied temporal changes of brain sodium and apparent diffusion coefficient (ADC) in a temporal lobe epilepsy (TLE) rat model using kainic acid (KA).

METHODS

In situ three-dimensional 23Na magnetic resonance imaging (MRI) and proton diffusion-weighted imaging (DWI) were used. KA at a dose of 10 mg/kg body weight and 12 adult Sprague Dawley rats weighing 228-318 g (268 +/- 25 g) were used.

RESULTS

Twenty-four hours after KA injection, magnetic resonance (MR) visible sodium levels increased in both the pyriform cortex (+90%) and amygdala (+68%) and increased insignificantly in the hippocampus (+18%) and caudate-putamen (12%). The ADC in the pyriform cortex showed a -9% decrease at 5 h postictally, reaching -30% at 24 h, whereas in the amygdala decreases were -8 and -26% respectively. A significant decrease in ADC (-7%) in the hippocampus was also observed 24 h postically. Seven days later, sodium increases persisted, whereas ADC returned to normal level.

CONCLUSIONS

The increase in MR visible sodium, associated with the decrease in ADC is consistent with the hypothesis that sequential seizures caused an increase in sodium influx and perturbation of membrane ion homeostasis, which eventually evolved into an irreversible phase of cellular edema, with increased MR visible intracellular sodium and decreased ADC. Return of ADC to near-control level and persistent high sodium level at 7 days may be explained by the increase in extracellular space and tissue necrosis.

Quantitative tissue sodium concentration mapping of normal rat brain

A quantitative in vivo method for obtaining maps of tissue sodium concentration (TSC) by MRI is compared to the invasive, global 22Na radionuclide dilutional technique in the normal rat brain. The MR method uses a three-dimensional projectional acquisition scheme to minimize signal losses from transverse relaxation. Internal calibration standards are used to convert the signal intensity into TSC after correction for B1 inhomogeneities by using the ratio of 23Na and 1H images obtained with identical B1 distributions and sensitivities at the two frequencies. Over the biological range of concentrations, the TSC, measured as the ratio of MR signals of 23Na and 1H, gives a linear response with concentration. In the normal rat brain, the mean TSC measured using the MRI method (TSC = 45 +/- 4 mM, animals = 5) is not significantly different from the global 22Na radionuclide method (TSC = 49 +/- 6 mM, animals = 7).

Effect of gossypol on cultured TM3 Leydig and TM4 Sertoli cells: 31P and 23Na NMR study

The effects of gossypol on glucose metabolism, ATP levels and intracellular sodium levels in murine TM3 Leydig and TM4 Sertoli cell lines were investigated, and their response compared. Relative ATP levels and sodium ion levels in the two cell lines were determined by 31P and 23Na NMR spectroscopy. Short-term effect of gossypol on phosphate metabolism in immobilized and perfused cells was apparent in 31P NMR spectra only with relatively high concentrations of gossypol, corresponding to about 40 times IC50. However, incubation with low gossypol concentrations markedly affected the energetic status of the cells, especially of the TM3 cells. Although inhibition of proliferation by gossypol was stronger with the TM4 cells, the decrease of intracellular ATP level and increase of sodium ion concentration were more pronounced in the TM3 cells. The growth-inhibitory effect of (-)-gossypol was stronger than that of (+)-gossypol, with the eudesmic ratio of 2-2.5. The enantioselectivity of the effect of gossypol on the energy metabolism of TM3 and TM4 cells was low, in contrast to the in vivo antispermatogenic effect, which was reported to be solely associated with (-)-gossypol. Inhibition of energy production in somatic testicular tissue is thus unlikely to be major cause of the antispermatogenic effect of gossypol.

MRI probes biophysical structure of cartilage

MRI of cartilage will likely remain a controversial topic for some time on account of disagreement over the appearance of normal cartilage and the accuracy of MRI for detecting early changes of osteoarthritis. This is an area, however, that may be amenable to the application of advanced imaging techniques, including magnetization transfer MRI, because of its relatively simple structure.

Binding of Ru(II) polyazaaromatic complexes to DNA: A 23Na NMR spin-lattice relaxation study

The possibility of using sodium-23 spin-lattice relaxation rate measurements to probe the interaction modes of Ru11 polyazaaaromatic complexes with DNA is investigated. The following complexes are considered: Ru(phen)3(2+) (phen = 1.10-phenanthroline), Ru(phen)2HAT2+ (HAT = 1,4,5,8,9,12-hexaazatriphenylene), and Ru(diMeTAP)3(2+) (diMeTAP = 2,7-dimethyl-1,4,5,8-tetraazaphenanthrene). The addition of Ru(diMeTAP)3(2+) to a solution of NaDNA leads to a decrease in the sodium-23 spin-lattice relaxation rate (R1) similar to the effect observed upon addition of Mg2+. This indicates that Ru(diMeTAP)3(2+) interacts like Mg2+ with DNA and consequently that the electrostatic interaction dominates the association with DNA, Ru(phen)3(2+) and Ru(phen)2HAT2+ diminish R1 more efficiently than Mg2+, in a manner similar to ethidium bromide, which is known for its intercalation properties. Thus interactions other than electrostatic occur between these two complexes and DNA. These results are in agreement with data obtained from other techniques, according to which Ru(phen)3(2+) and Ru(phen)2HAT2+ are located partially inside the DNA double helix, in contrast to Ru(diMeTAP)3(2+) which remains in the ionic atmosphere around the phosphate backbone.

1H, 29Si and 1H, 23Na heteronuclear shift correlation in octosilicate via cross-polarisation

Solid-state magic-angle spinning was used to study octosilicate, a layered sodium polysilicate hydrate. Conventional one-dimensional NMR spectra detect two distinct proton and silicon sites and a single sodium species. Heteronuclear shift correlation experiments have shown that only one type of proton is involved in efficient cross-polarisation to all the silicon and sodium sites. Such selectivity could be caused by a favourable position for, and suitable rigidity of, this strongly hydrogen-bonded proton. The latter requirement can be used to propose a simple model of the interlayer space in octosilicate.

Ionophore properties of monensin derivatives studied on human erythrocytes by 23Na NMR and K+ and H+ potentiometry: relationship with antimicrobial and antimalarial activities

Eight derivatives of monensin with a modified C25-C26 moiety were synthesized. Their ionophore properties were studied on human erythrocytes by measuring Na+ influx with 23Na NMR and concomitant K+ and H+ efflux by potentiometry. Modification of OH-26 led to inversion of selectivity of transport in favor of K+/Na+ in comparison with monensin. This selectivity disappeared by suppression of the C26-OH moiety. Finally the ionophore ability was lost if the head-to-tail chelation of the monensin skeleton was prevented by blocking the terminal OH-25 and -26 functions. All the compounds were inactive on Gram-negative bacteria and fungi. MIC measured on Bacillus cereus showed that derivatives with increased K+/Na+ selectivity were clearly the most active against Bacillus growth. Most of the compounds showed potential antimalarial properties in the nanomolar range when tested in vitro against Plasmodium falciparum. The IC50S measured were correlated with the whole Na+ and K+ transport efficiency rather than with the ionic selectivity. In both cases determination of initial fluxes of transport for both cations (Na+ and K+) was necessary to investigate the relationship between biological and ionophore properties.

Solid state NMR characterisation of crystalline Na2O-ZrO2-SiO2 phases

The NMR interactions of crystalline phases in the system Na2O-ZrO2-SiO2 have been studied by a combination of static and magic angle spinning NMR methods for the first time. A full multinuclear (17O, 23Na, 29Si and 91Zr) approach has been employed that allows the phases to be clearly identified. NMR interactions such as 29Si isotropic chemical shift correlate with the known structural units present. For 23Na the the different sites can often be distinguished on the basis of differing quadrupolar interactions.

Off-resonance effects on 2D NMR nutation spectra of I = 3/2 quadrupolar nuclei in static samples

The off-resonance effects on 2D NMR nutation of I = 3/2 quadrupolar nuclei are demonstrated with perturbation theory and numerical calculation in static samples. The off-resonant (delta omega) rf field (omega 1) enlarges a nutation frequency and consequently increases the measurement range of nuclear quadrupolar interaction parameters. When omega e > omega Qmax, and arctg(omega 1/delta omega) = +/- 54.7 degrees (magic angle), the satellite lines (produced by coherence transfers) in a nutation spectrum are superimposed with the line of central transition, and hence the nutation spectrum is simplified and its sensitivity is enhanced. The nuclear quadrupolar interaction parameters of 23Na nuclei in Na omega molecular sieve are obtained using 2D NMR nutation.

23Na and 31P nuclear magnetic resonance studies of ischemia-induced ventricular fibrillation. Alterations of intracellular Na+ and cellular energy

To clarify the role of Na+i, pHi, and high-energy phosphate (HEP) levels in the initiation and maintenance of ischemia-induced ventricular fibrillation (VF), interleaved 23Na and 31P nuclear magnetic resonance spectra were collected on perfused rat hearts during low-flow ischemia (51 minutes, 1.2 mL/g wet wt). When untreated, 50% of the hearts from normal (sham) rats and 89% of the hypertrophied hearts from aorticbanded (band) rats (P < .01 versus sham) exhibited VF. Phosphocreatine content was significantly higher in sham than band hearts during control perfusion (53.3 +/- 1.6 versus 39.8 +/- 2.0 mumol/g dry wt). Before VF at 20 minutes of ischemia, Na+i accumulation was greater in hearts that eventually developed VF than in hearts that did not develop VF for both band and sham groups (144% versus 128% of control in sham; P < .005) and was the strongest metabolic predictor of VF; ATP depletion was also greater for VF hearts in the sham group. Infusion of the Na(+)-H+ exchange inhibitor 5-(N,N-hexamethylene)-amiloride prevented VF in sham and band hearts; reduced Na+i accumulation but similar HEP depletion were observed compared with VF hearts before the onset of VF. Rapid changes in Na+i, pHi, and HEP began with VF, resulting in intracellular Na+i overload (approximately 300% of control) and increased HEP depletion. A delayed postischemic functional recovery occurred in VF hearts, which correlated temporally with the recovery of Na+i. In conclusion, alterations in Na+i were associated with spontaneous VF transitions, consistent with involvement of excess Na+i accumulation in VF initiation and maintenance and with previously reported alterations in Ca2+i with VF.(ABSTRACT TRUNCATED AT 250 WORDS)

Gadolinium and dysprosium chelates of DTPA-amide-dextran: synthesis, 1H NMR relaxivity, and induced 23Na NMR shift

In this study the conjugated macromolecular ligand, diethylenetriaminepentaacetic acid (DTPA)-amide-dextran, was synthesized by attaching DTPA to the dextran macromolecule (M(r) approximately 6000) by a covalent amide bond. Subsequently, DTPA-amide-dextran was complexed with either of the two lanthanide metal ions dysprosium (Dy) or gadolinium (Gd). The paramagnetic 23Na NMR shift induced by Dy(DTPA-amide-dextran) and the relaxivity (rho 1) induced by Gd(DTPA-amide-dextran) were characterized. Dy(DTPA-amide-dextran) induced a 25% larger 23Na NMR shift than that induced by Dy(DTPA). Neither the shift induced by Dy(DTPA-amide-dextran) nor the shift induced by Dy(DTPA) was affected by increasing levels of calcium ions in the solution. offDTPA-amide-dextran) exhibited an in vitro rho 1 of 8.4 (mM s)-1 at a 0.23 T magnetic field and 9.3 (mM s)-1 at a 0.47 T magnetic field, thus indicating a positive magnetic field dependence.

31P NMR and triple quantum filtered 23Na NMR studies of the effects of inhibition of Na+/H+ exchange on intracellular sodium and pH in working and ischemic hearts

The triple quantum filtered 23Na NMR method is applied here to measure the effects of EIPA, a specific inhibitor of the Na+/H+ antiporter, on relative intracellular sodium concentrations in isolated working hearts at baseline, during ischemia, and at subsequent reperfusion. In analogy to the spectrophotometric isosbestic point, an approach is developed that defines a value of tau at which the effect of the relaxation times on the TQF signal intensities is minimized, and the signals are proportional to the sodium concentration for both ischemic and working hearts. EIPA at 1.5 microM significantly inhibited (P < 0.01) the influx of intracellular Na+ during 20 min of ischemia at 36.2 degrees C in this rat heart model. In parallel 31P NMR studies, EIPA had no effect on either the development of acidosis during ischemia or on the recovery of pHi during reperfusion despite its profound effect on intracellular Na+ influx. Thus, under our conditions the Na+/H+ antiporter did not play a critical role in the maintenance of intracellular pH. EIPA treatment resulted in improved recovery (P < 0.005) of mechanical function after 20 min of ischemia. [ATP] was higher in treated hearts during ischemia and reperfusion.

Relationships between cytosolic [ATP], [ATP]/[ADP] and ionic fluxes in the perfused rat heart: A 31P, 23Na and 87Rb NMR study

In order to assess the relationship between cytosolic [ATP] or [ATP]/[ADP] and the intracellular Na+ concentration ([Na+]i), we have used the phosphate trap 2-deoxy-D-glucose (DG) to alter the high energy phosphate levels in rat cardiomyocytes. Pyruvate-perfused rat hearts were treated with 2 mM DG in the presence of 10IU/l of insulin for 28 min, followed by perfusion with DG without insulin for 60 min. The DG + insulin treatment resulted in dramatic changes in the 31P NMR spectra: phosphocreatine (PCr) and total ATP decreased (to 15 and 35%, respectively) and deoxyglucose-6-phosphate accumulated, with little change in either inorganic phosphate or intracellular pH. These changes corresponded to a decrease in cytoplasmic [ATP] (from 7.6 to 1.8 mM), [ATP]/[ADP] (from 494 to 24) and ATP affinity [A(ATP), by 8.9 kJ/mol] and an increase in [ADP] (five-fold) and free [Mg2+] (two-fold). Subsequent perfusion with DG--insulin resulted in slow recovery of PCr, [ATP]/[ADP] and A(ATP) such that the "low energy" state lasted an additional 16 min during which ATP remained low and constant. There were no detectable changes in the intracellular Na+ content as assessed by shift reagent-aided 23Na NMR at the end of DG + insulin treatment (98 +/- 18%, 28-36 min of the protocol). In addition, there was no change in the Rb+ influx rate as measured by 87Rb NMR at the beginning of insulin washout which was achieved by replacing 20% of the KCl with RbCl ([K+] = 3.76 mM, [Rb+] = 0.94 mM). During DG + insulin treatment the pressure-rate product (PRP) decreased by half and was restored upon insulin washout to 80% of its initial value both in the presence and in the absence of the shift reagent [5 mM Dy (triethylenetetraminehexaacetate)3-]. These data imply that unfavorable thermodynamic [low A(ATP)] and kinetic (low [ATP] and [ATP]/[ADP]) conditions induced by DG treatment do not inhibit Na+, K(+)-ATPase activity. We speculate that during anoxia when changes in [ATP]/[ADP] are comparable to those induced by DG treatment, the observed increase in [Na+]i is not due to inhibition of the Na+ pump by reduced [ATP] or [ATP]/[ADP].

23Na NMR detects protection by glycine and alanine against hypoxic injury in the isolated perfused rat kidney

Protection against hypoxic injury by supraphysiological glycine and alanine concentrations was investigated in the isolated perfused rat kidney (IPRK). 23Na NMR detects consistent increases in total renal Na in IPRK during hypoxic perfusion. Increasing the concentration of glycine and alanine to 5 mM each produced a 34% (p < 0.001) reduction in the increase in total renal Na following 30 minutes of hypoxia compared to a matched control group supplemented with 5 mM each of serine and glutamine. There was also a trend (p = 0.067) to improvement in the fractional excretion of sodium (FENa) in the glycine plus alanine treated group. Hypoxic alterations of other physiological parameters were not prevented by supraphysiological glycine plus alanine. This suggests that monitoring total renal Na is a more sensitive method of defining renal injury and protection than monitoring changes in FENa, fractional excretion of potassium (FEK) and inulin clearance.

Three-dimensional triple-quantum-filtered imaging of 0.012 and 0.024 M sodium-23 using short repetition times

The gradient-selected triple-quantum-filtered (GS3Q) experiment, developed to improve the contrast in NMR imaging of sodium-23 (23Na) in the human brain, is limited by low signal-to-noise ratio (SNR). We have analyzed the GS3Q experiment and show here that the improvement in GS3Q-filtered 23Na SNR as the repetition time (TR) decreases is accompanied by the appearance of spurious one-quantum (1Q) 23Na signals. An improved filter with better suppression of spurious 1Q 23Na signals is obtained by adding a preparatory crusher gradient and two-step phase cycling to a conventional GS3Q filter. The relative contributions of 3Q coherence and spurious 1Q coherences to the conventional and modified-GS3Q-filtered signals are calculated, providing a measure of the effectiveness of each GS3Q filter. The filters were implemented on a 2.35 T medium-bore spectrometer and their predicted properties verified. SNR measurements from GS3Q-filtered three-dimensional images of an agarose gel phantom indicate that 0.012 M 23Na images in the human brain can be acquired with 8 cm3 voxels and SNR of 10 in 30 minutes at 2.35 T, assuming similar relaxation times.

The influence of acetazolamide and amlodipine on the intracellular sodium content of rat proximal tubular cells

1. This investigation set out to use 23Na n.m.r. spectroscopy to measure changes in intracellular levels of sodium in isolated suspensions of rat proximal tubules. The effects of temperature, an inhibitor of the sodium pump and known natriuretic drugs on intracellular sodium content of such tubular preparations were measured and compared with calcium channel antagonists where action at this level is unclear. 2. Rat kidneys were perfused with collagenase, roughly chopped, subjected to mechanical dispersion and washed to remove all traces of the enzyme. The proximal tubules were then purified and concentrated by Percoll density gradient centrifugation and then resuspended in buffer containing dysprosium tripolyphosphate shift reagent. 3. Distinct peaks corresponding to intracellular and extracellular sodium signals were observed when the tubules were placed into the n.m.r. spectrometer. As the temperature of the suspension rose to 37 degrees C, there was an exponential decrease in sodium content, with a decay constant of 0.15 +/- 0.02 min-1, which reached a stable level within 20 to 25 min. Addition of ouabain, 10(-3) M, resulted in a significant (P < 0.01) 30% increase in intracellular sodium content within 5 min which peaked at 70% 20 min later. Although acetazolamide (10(-3) M) significantly (P < 0.01) increased intracellular sodium content by 45%, amlodipine (10(-4) M) had no effect. 4. These data show that changes in the activity of the Na+/K+/ATPase have a considerable influence on the intracellular levels of sodium in proximal tubule cells. Inhibition of carbonic anhydrase activity resulted in a rise in intracellular sodium content which is compatible with its action to reduce the turnover rate of the Na+/(HCO3-)3 symporter. The lack of effect of amlodipine was consistent with the suggestion that it does not have a direct action on the sodium handling processes at the level of the proximal tubule.

In vivo studies of cellular energy state, pH, and sodium in rat liver after thermal injury

In vivo 31P- and 23Na-magnetic resonance spectroscopy was used to measure phosphorus metabolites, intracellular pH, cytosolic free Mg2+, and intracellular Na+ in the liver of rats 24 h after 40% total body surface area full-thickness burn injury. Studies were performed during infusion of thulium (III) 1,4,7,10-tetraazacyclododecane N,N',N",N"'-tetra(methylenephosphonate), which served as the Na+ shift agent. Compared with the sham-burn group, there was a significant increase in hepatic intracellular Na+ along with a decrease in intracellular pH and free Mg2+. The ratio of intra- to extra-cellular Na+ increased, indicating a decreased Na+ gradient that may determine the hepatic transmembrane potential difference. Hepatic beta-ATP/P(i) also significantly decreased, which suggests that either ATP utilization is significantly accelerated or ATP synthesis is inhibited after the thermal injury. Of the cations measured (Na+, Mg2+, H+), the change in intracellular Na+ was most dramatic. This study demonstrates that major burn injury may cause profound changes in hepatic bioenergetics and ionic metabolism 24 h after injury and that intracellular Na+ may be a sensitive indicator of hepatic dysfunction 24 h after injury. Because these animals tolerated the shift reagent, thulium (III) 1,4,7,10-tetraazacyclododecane N,N',N",N"'-tetra(methylenephosphonate), nuclear magnetic resonance spectroscopy may prove valuable in monitoring intracellular cations in the liver after major injury.

23Na- and 1H-NMR studies of the action of chlorpromazine and imipramine on nigericin-mediated Na+ transport across phosphatidylcholine vesicular membranes

In order to elucidate the action of chlorpromazine (CPZ) and imipramine (IMP) on nigericin-mediated Na+ transport across phosphatidylcholine vesicular membranes, 23Na nuclear magnetic resonance was applied to the exchange system of Na+ ions present at the same concentration inside and outside unilamellar vesicles. CPZ and IMP added to the vesicles in micromolar concentrations produced an equal increase in the carrier-transport rate. The kinetic analysis, together with 1H-NMR observations of the reduction in membrane fluidity produced by the drugs and on the direct interaction between drugs and nigericin, allowed us to conclude that the drug-induced promotion of transport occurred not from the formation step of the Na(+)-nigericin complex nor from its diffusion step, but from its dissociation step. The formation of an adduct between drug and nigericin could be the cause of the drug effect and this proceeded much more efficiently at a membrane-water interface (stability constant Kb; 3 x 10(5) M-1) than in methanol (Kb; 5 x 10(2) M-1). The reason for the difference is also discussed.

Erythrocyte Na-K-Cl cotransport activity in low renin essential hypertensive patients. A 23Na nuclear magnetic resonance study

The Na-K-Cl cotransport activity in red blood cells from essential hypertensive men with low (n = 8, mean age 42 +/- 4 years) or normal renin activity (n = 4, mean age 43 +/- 3 years), and in normotensive men with normal renin activity (n = 7, mean age 38 +/- 4 years) has been evaluated by means of a recently developed 23Na nuclear magnetic resonance (NMR) method. Sodium efflux was determined by relating the resonating frequency of the NMR signal from extracellular sodium to sodium concentration in the presence of the shift reagent Dy(PPP)2(7-). The maximum Na+ efflux driven by cotransport (Vmax) was measured in Na(+)-loaded erythrocytes in the presence of ouabain to block the Na-K-Cl pump activity. A significant difference (P < 0.05) was found in Vmax values of low renin patients (0.70 mmol/h/L cells, range 0.40 to 0.90 mmol/h/L cells) as compared with normotensive controls (0.39 +/- 0.08 mmol/h/L cells) and normal renin hypertensives (mean 0.49 +/- 0.04 mmol/h/L cells). In conclusion, this study showed an increased activity of the Na-K-Cl cotransport in red blood cells from low renin hypertensive men as compared with normal renin hypertensives and normotensives.

Analysis of double-quantum-filtered NMR spectra of 23Na in biological tissues

Double-quantum-filtered NMR spectra of 23Na in bovine nasal cartilage tissue and its constituents were measured. The presence of even-rank tensors was detected in the cartilage tissue and in a suspension of collagen fibers, indicating anisotropic motion of the sodium ions. Quantitative analysis of the spectra was performed by calculating the time evolution of the second- and third-rank tensors by solving a modified Redfield equation. Analytical expressions for the spectra were obtained. It is shown that the anisotropy stems from local rather than macroscopic order. A good fit to the observed spectra was obtained for several models that assume isotropic distribution of the directors of the locally ordered sites. The local residual quadrupolar interaction was found to be 550 Hz, demonstrating the sensitivity of double-quantum filtration in the detection of anisotropic motion.

Adsorption of Na+ onto gamma-alumina studied by solid-state 23Na and 27Al nuclear magnetic resonance spectroscopy

The adsorption of Na+ on gamma-alumina surfaces at four coverages of Na2CO3[5, 10, 15 and 20% w/w)] was characterized by solid-state 23Na and 27Al nuclear magnetic resonance (NMR) spectroscopy. The experimental results suggest that two distinct adsorbed species are present on the alumina surface: surface species and surface salts. At the lower coverages of Na2CO3 (5 and 10%), the surface species is predominant, in which the Na+ cations are associated with the oxygen atoms of gamma-alumina. Increasing the loading level to 15% results in the appearance of a second adsorbed species that is attributed to the surface salt, Na2CO3, deposited on the solid surface. Further adsorption of Na2CO3 leads to an increase in the amount of surface salt while the amount of surface species remains unchanged. 1H-27Al Cross-polarization magic angle spinning (CP-MAS) experiments give the evidence that some Na+ cations in the form of surface species are coordinated with the Brönsted acid sites of gamma-alumina. This may be the main driving force that improves appreciably the catalytic efficiency of an Na2CO3-Al2O3 catalyst.

Complete elimination of the extracellular 23Na NMR signal in triple quantum filtered spectra of rat hearts in the presence of shift reagents

A method is suggested whereby the shifted extracellular triple quantum filtered 23Na signal of an isolated organ is completely eliminated. The method is based on the long relaxation time of the triple quantum coherence and on its fast evolution rate. When the carrier frequency is set on top of the intracellular sodium signal and the time interval between the last two pulses to (12 delta nu)-1 (delta nu is the frequency difference between the intracellular and the extracellular signals), a complete elimination of the extracellular 23Na signal is achieved. The method is demonstrated for isolated rat hearts and the quantification of intracellular sodium using triple quantum filtered spectroscopy is discussed.

Characterization of sodium cations in dehydrated faujasites and zeolite EMT by 23Na DOR, 2D nutation, and MAS NMR

Sodium cations localized at crystallographically distinct cation sites in dehydrated zeolites were characterized using 23Na double rotation, two-dimensional nutation, and magic-angle-spinning nuclear magnetic resonance spectroscopy. The new DOR NMR technique has been applied at different magnetic field strengths to determine the quadrupole parameters of the overlapping quadrupole patterns. In the NMR spectra of dehydrated NaY and NaEMT two signals of sodium cations were identified, a low-field gaussian line at -12 +/- 1 ppm and a high-field quadrupole pattern, with an isotropic chemical shift of -8 +/- 1 ppm and a quadrupole coupling constant of about 4 MHz. By comparison of the 23Na MAS NMR intensities of these signals with the population of the cation sites determined by XRD and by calculation of the electric field gradients, the former signal was attributed to sodium cations at the sites SI and the latter one to sodium cations at the sites SI' as well as SII in faujasite and zeolite EMT. This assignment has further been confirmed by 23Na MAS NMR studies of dehydrated HNaY and BaNaY zeolites.

Cardiac glycoside-induced elevation of intracellular Na+ ion concentration in human erythrocytes studied by 23Na NMR spectroscopy: relationship between inotropy speed and elevation rate of intracellular Na+ ion concentration

Elevation of intracellular sodium ion concentration in human erythrocyte induced by the cardiac glycoside, proscillaridin, and its four derivatives was measured using 23Na NMR spectrometry. In this examination, there was a significant correlation between the time to half maximum inotropic effect and the time to maximum of Na+ concentrations in human erythrocyte, determined by 23Na NMR.

In vivo Na-23 MR imaging and spectroscopy of rat brain during TmDOTP5- infusion

In vivo sodium-23 and hydrogen-1 magnetic resonance (MR) imaging and spectroscopy of the rat brain during infusion of the shift reagent thulium DOTP5- (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra[methylene phosphonate] was performed to assign the various peaks observed during infusion and to evaluate the shift reagent in discriminating tissue compartments. Na-23 spectra collected during the infusion showed two shifted peaks that were assigned to intravascular Na+ and extracellular muscle Na+, respectively, and one unshifted peak assigned to intra- and extracellular brain Na+ and cerebrospinal fluid Na+. These assignments were validated with H-1 and Na-23 MR imaging and Na-23 chemical shift imaging (CSI). The H-1 and Na-23 images showed that a surface coil placed on a rat head can detect a substantial amount of signal from muscle surrounding the skull. Na-23 CSI spectra from successive 1-mm-thick coronal sections indicated that the shift reagent did not cross the blood-brain barrier. The study also showed that bulk susceptibility shifts are quite small with Tm-DOTP5-. This reagent may be useful in determining compartmental Na+ concentrations and blood flow kinetics in brain and in examining the integrity of the blood-brain barrier.

Sodium-23 and lithium-7 NMR spin-lattice relaxation measurements in the study intercalation in DNA

Sodium-23 spin-lattice relaxation rate (the reciprocal relaxation time) measurements have been used to study the intercalation of 9-aminoacridine in calf thymus DNA. The results are analyzed by a two state model based on the counterion condensation theory and a theory for the quadrupolar relaxation of counterions in polyelectrolyte solutions. It is shown that change of the solvent from H2O to D2O has a negligible effect on the intercalation process. Furthermore, an attempt is made to analyze the dependence of the 7Li spin-lattice relation rate on intercalation of 9-aminoacridine in LiDNA. It is shown that both quadrupolar and dipolar mechanisms contribute to the bound 7Li relation rate, and that both these contributions are reduced upon intercalation of 9-aminoacridine.

Sodium-23 MR imaging of the kidney in guinea pig at 2.1 T, following arterial, venous, and ureteral ligation

In vivo 23Na magnetic resonance images of guinea pig kidney were obtained at 2.1 T using a spin-echo sequence with an echo time of 19 ms. The intact kidney showed a very strong signal intensity in the sodium image. The signal intensity of the kidney decreased to 55% after ligation of the renal artery together with the vein and the ureter. The total sodium content in the excised kidney after arterial occlusion, measured by flame photometry, was 24% higher than that in the intact kidney. The transverse relaxation time (T2) of the extracellular sodium in the isolated kidney decreased to one-third of that in the intact kidney. This shortening of T2 may be partly responsible for the decrease in the 23Na signal intensity from the kidney after arterial occlusion.

In vivo propionate oxidation as a prognostic indicator in disorders of propionate metabolism

Biochemical markers such as plasma and urinary metabolite concentrations and in vitro enzyme activity are of limited prognostic value in the most common disorders of propionate metabolism, methylmalonic acidaemia (MMA) and propionic acidaemia (PA). In vivo propionate oxidation was compared with conventional prognostic measures as predictors of clinical severity in seven children with MMA and six with PA. Propionate oxidation was measured using a continuous infusion of [1-13C]propionate and was expressed as the rate of appearance of 13CO2 as a percentage of the propionate infusion rate. Children with MMA (mean oxidation 51.2%, range 17.5-91.6, P less than 0.05) and with PA (mean oxidation 36.3%, range 3.0-91.1, P = NS) oxidised substantially less propionate than controls (mean oxidation 81.9%, range 69.4-101.0, n = 5). Percentage oxidation was a better predictor of the clinical severity score (r = 0.75, P less than 0.01) than was in vitro enzyme activity, plasma propionate or methylmalonate concentration or urinary metabolite excretion. Studies were repeated after an interval of 1-3 weeks in six of the subjects; the percentage oxidation in each subject was virtually unchanged between studies (coefficient of variation 8.6%). These results suggest that in vivo oxidation measurements using [13C]propionate are both reproducible and prognostically useful in disorders of propionate metabolism.

Protection of liposomes during dehydration or freezing

When liposomes are subjected to dehydration or freeze-thawing, vesicle fusion and/or leakage of vesicle contents can occur. The disaccharide, trehalose and the cryoprotectant, glycerol, are known to protect vesicle integrity during dehydration and freezing respectively. Here we examine their protective abilities as a function of vesicle size and lipid composition. It is shown that fatty acyl composition, cholesterol content and, with the exception of phosphatidylglycerol, acidic lipid content do not significantly alter the retention of aqueous contents by vesicles dehydrated and rehydrated in the presence of trehalose. The susceptibility to leakage induced by both dehydration and freezing is, however, critically dependent upon vesicle size with the smallest systems (70-100 nm diameter) being most stable. The mechanism whereby trehalose protects against vesicle fusion and leakage is also discussed.

Regional T2 and sodium concentration estimates in the normal human brain by sodium-23 MR imaging at 1.5 T

We have analyzed multiple spin echo Na magnetic resonance (MR) images of the normal human brain in four volunteer subjects. Utilizing the much slower T2 decay of the CSF, we obtained images that separate cortex from the surrounding CSF and measured regional T2 of cortex, white matter, CSF, vitreous humor, and superior sagittal sinus. Assuming a sodium concentration of 145 mM in the vitreous humor, we normalized the extrapolated equilibrium magnetization (M0) for each region to the M0 of the vitreous humor to estimate regional sodium concentration. We found that regional T2 measurements more consistently distinguish the high signal regions of cortex, CSF, and blood than do our regional sodium estimates, whereas regional sodium estimates adequately distinguish white matter from cortex. The T2 values of white matter and cortex, on the other hand, are nearly identical. Our work addresses the problems encountered in establishing norms for clinical application of Na MR and represents a step toward establishing those norms.

The monensin-mediated transport of Na+ and K+ through phospholipid bilayers studied by 23Na- and 39K-NMR

Addition of monesin to preparations of large unilamellar vesicles made from egg yolk phosphatidylcholine (EPC) in sodium or potassium chloride solution and from dioleoylphosphatidylcholine (DOPC) in sodium chloride solutions gives rise to dynamic 23Na- and 39K-NMR spectra. The dynamic spectra arise from the monensin-mediated transport of the metal ions through the membrane. The kinetics of the transport are followed as a function of monensin and metal ion concentrations and are compatible with a model in which one monensin molecule transports one metal ion. Rate constants for the association and dissociation of the monensin-metal complex in the membrane/water interface are extracted and the stability constants for complex formation are evaluated. The rate constants in DOPC are similar to those in EPC, confirming that diffusion is not rate-limiting in the transport process and that dissociation of the complex is the rate-limiting step. Although potassium on its own is transported more rapidly, sodium forms the more stable complex and is therefore transported preferentially in competition with potassium.

23Na nuclear magnetic resonance study of Na+-K+ pump inhibition by a fraction from uremic toxins

An in vitro inhibitor of Na+/K+-transporting ATPase (EC 3.6.1.37) was isolated from uremic plasma and normal urine by liquid chromatography. A 23Na nuclear magnetic resonance study involving living erythrocytes showed that this inhibitor causes impairment of the Na+-K+ pump of intact erythrocytes. This finding may explain the high intra-erythrocytic sodium concentration in those uremic patients exhibiting a high concentration of this inhibitor. The presence of this same inhibitor in normal urine suggests that it may play a physiological role.

The flip-angle effect: a method for detection of sodium-23 quadrupole splitting in tissue

A method is presented for the detection of quadrupole splitting in tissue, where the spectral line splittings are typically unobservable. The method used is a study of the rate of rotation of the flip angle as a function of radiofrequency (rf) amplitude. Our results with samples of skeletal muscle and cat brain indicate the absence of quadrupole splitting.

23Na NMR spectroscopy of proximal tubule suspensions

Intracellular sodium concentrations in proximal tubule suspensions of rat kidney were measured by NMR spectroscopy. A simple method for the preparation of proximal tubule suspension is described. Examination by light microscopy revealed these preparations to contain 93.6 +/- 0.6% (N = 5) proximal tubules, and electron microscopy demonstrated that the tubules were open. When incubated with trypan blue for five min, only 2% of tubules picked-up the dye. The basal oxygen consumption rate was 0.42 +/- 0.01 microliter min-1 mg protein-1 (N = 6). Addition of succinate (5 mM) resulted in a fivefold increase in the rate of oxygen consumption. The 23Na spectra were obtained in proximal tubules incubated for 30 min in the aqueous shift reagent dysprosium tripolyphosphate Dy(PPPi)2(7-). The NMR observable sodium concentration was 34.1 +/- 1.8 mM at room temperature and 16.3 +/- 0.6 mM (P less than 0.001) at 37 degrees C. Addition of ouabain (10(-4) M) at 37 degrees C resulted in an increase in intracellular sodium to 30.9 +/- 2.9 mM (P less than 0.001), while nystatin increased the concentration of sodium to 72.0 +/- 9.1 mM (P less than 0.001), compared to basal concentration. Thus NMR permits the measurement of intracellular concentration of sodium in proximal tubules under basal conditions and to monitor, in the same preparation, the changes that occur under various experimental conditions without interfering with the morphologic integrity of the cells.

Evidence from 23Na NMR studies for the existence of sodium-channels in the brush border membrane of the renal proximal tubule

A fast Na+-exchange is shown to be present in isolated renal brush border membranes. The lower limit of the rate constant for this process, calculated from the 23Na-NMR spectrum is 580 sec-1. The actual exchange rate may be higher. A fast 7Li exchange is also shown to be present in the isolated membrane vesicles. The characteristic overshoot of the Na+ dependent D-glucose cotransport and Na+/H+ antiport can be demonstrated. The fact that neither treatment with papain, nor lowering of the temperature to 5 degrees C affected the 23Na-NMR spectra obtained in the renal brush border membrane vesicles is consistent with the possibility that the fast Na+-exchange occurs through a channel mechanism.

In vivo sodium-23 magnetic resonance surface coil imaging: observing experimental cerebral ischemia in the rat

Sodium-23 magnetic resonance imaging can be used to detect and assess experimental cerebral ischemia in the rat. An imaging technique utilizing a surface coil is described to produce sodium magnetic resonance images of good quality and resolution within 10 min. A novel method of hemispheric occlusion showed edema in the right brain of the rat head within 3 hr after injury. The edema was especially pronounced by 12 hr with effects in the right brain, eye and surrounding muscle evident.

23Na NMR maps of head sized phantoms and a low resolution 23Na map of the live human head

An NMR system capable of obtaining 23Na NMR signals and scans from large objects containing biological concentrations of sodium in a 411 gauss magnetic field in less than one hour was developed. Scans were carried out on 6"-8" diameter phantoms containing 150 mM NaCl and the first low resolution 23Na NMR map of a live human head was obtained.

Use of the double-isotope single-injection method for estimating renal function in normal cross-bred swine

The double-isotope single-injection method to estimate renal function which utilizes the radiolabeled chemicals [131I]sodium iodohippurate and [125I]sodium iothalamate was evaluated in swine. A total of 46 normal, cross-bred swine were used to determine the applicability of this method for measuring the glomerular filtration rate and effective renal plasma flow. The mean glomerular filtration rate in pigs was determined to be 5.33 +/- 0.82 ml/kg of body weight/minute for [125I]sodium iothalamate with a biological half-life (T 1/2) of 39.18 +/- 7.44 minutes. The mean effective renal plasma flow was determined to be 19.25 +/- 3.12 ml/kg of body weight/minute for [313I]sodium iodohippurate, with a T 1/2 of 18.45 +/- 1.74 minutes. These values are more closely related to the glomerular filtration and effective renal plasma flow values reported for dogs and cats than they are to values reported for man. The method is rapid and reliable; results are available 6 to 8 hours after the experiment. This method is advantageous when information about renal function variables is a prerequisite to pharmacokinetic or toxicologic studies.