A method for measuring intra-tissue swelling pressure using a needle micro-osmometer.

The intervertebral disc's ability to resist load and facilitate motion arises largely from osmotic swelling pressures that develop within the tissue. Changes in the disc's osmotic environment, diurnally and with disease, have been suggested to regulate cellular activity, yet knowledge of in vivo osmotic environments is limited. Therefore, the first objective of this study was to demonstrate proof-of-concept for a method to measure intra-tissue swelling pressure and osmolality, modeling micro-osmometer fluid flux using Darcy's law. The second objective was to compare flux-based measurements of the swelling pressure within nucleus pulposus (NP) tissue against ionic swelling pressures predicted by Gibbs-Donnan theory. Pressures (0.03- 0.57 MPa) were applied to NP tissue (n = 25) using equilibrium dialysis, and intra-tissue swelling pressures were measured using flux. Ionic swelling pressures were determined from inductively coupled plasma optical emission spectrometry measurements of intra-tissue sodium using Gibbs-Donnan calculations of fixed charge density and intra-tissue chloride. Concordance of 0.93 was observed between applied pressures and flux- based measurements of swelling pressure. Equilibrium bounds for effective tissue osmolalities engendered by a simulated diurnal loading cycle (0.2-0.6 MPa) were 376 and 522 mOsm/kg H2O. Significant differences between flux and Gibbs-Donnan measures of swelling pressure indicated that total tissue water normalization and non-ionic contributions to swelling pressure were significant, which suggested that standard constitutive models may underestimate intra-tissue swelling pressure. Overall, this micro-osmometer technique may facilitate future validations for constitutive models and measurements of variation in the diurnal osmotic cycle, which may inform studies to identify diurnal- and disease-associated changes in mechanotransduction.

Oxidative impairment in scrapie-infected mice is associated with brain metals perturbations and altered antioxidant activities.

Prion diseases are characterized by the conversion of the normal cellular prion protein (PrP(C)) into a pathogenic isoform (PrP(Sc)). PrP(C) binds copper, has superoxide dismutase (SOD)-like activity in vitro, and its expression aids in the cellular response to oxidative stress. However, the interplay between PrPs (PrP(C), PrP(Sc) and possibly other abnormal species), copper, anti-oxidation activity and pathogenesis of prion diseases remain unclear. In this study, we reported dramatic depression of SOD-like activity by the affinity-purified PrPs from scrapie-infected brains, and together with significant reduction of Cu/Zn-SOD activity, correlates with significant perturbations in the divalent metals contents. We also detected elevated levels of nitric oxide and superoxide in the infected brains, which could be escalating the oxidative modification of cellular proteins, reducing gluathione peroxidase activity and increasing the levels of lipid peroxidation markers. Taken together, our results suggest that brain metal imbalances, especially copper, in scrapie infection is likely to affect the anti-oxidation functions of PrP and SODs, which, together with other cellular dysfunctions, predispose the brains to oxidative impairment and eventual degeneration. To our knowledge, this is the first study documenting a physiological connection between brain metals imbalances, the anti-oxidation function of PrP, and aberrations in the cellular responses to oxidative stress, in scrapie infection.

Investigation of Cr(III) hydrolytic polymerisation products by capillary electrophoresis-inductively coupled plasma-mass spectrometry.

The development of a new method for the determination of Cr(III) hydrolytic polymerisation products using capillary electrophoresis-inductively coupled plasma mass spectrometry (CE-ICP-MS) is described. The results indicate that CE-ICP-MS can be used to separate and detect monomeric and polymeric Cr(III) species. The various species migrate through the capillary at a rate proportional to their equilibrium distribution, which is dictated by the solution pH, metal ion concentration and ageing period. In general, the data suggest that the relative mobility follows the order trimer>dimer>monomer. The experimentally determined speciation shows a good qualitative agreement with that described in the literature. Independent confirmation of the presence of polymeric Cr(III) species was performed by ionspray mass spectrometry.

Metabolism of selenite in men with widely varying selenium status.

OBJECTIVE: This study was undertaken to investigate the metabolism of selenite in men with life-long intakes of deficient, adequate and excess selenium. METHODS: Stable isotopes of selenium were infused for five hours into Chinese men living in deficient, adequate or excessive selenium areas, and 24-hour urine and blood samples were collected daily for the next seven days. Stable isotopic selenium excretion was determined in urine and in whole plasma and plasma fractions. RESULTS: Even though there was a positive correlation of selenium intake with the urinary excretion of this element, this relationship was not linear over the entire range (deficient, adequate, excessive) of selenium intake. When the urine excretion was normalized internally within each group, a sharp increase in the slope of this relationship was found when long-term intake increased to adequate amounts, but the slope reached a plateau when the daily intake exceeded the adequate group. The plasma selenoprotein P fraction was labeled initially, but the incorporation in the glutathione peroxidase fraction subsequently increased by a small amount. A two-month dietary restriction of selenium of the subjects from the excess area did not result in a reduction of urinary excretion of infused selenite. CONCLUSION: A complex relationship exists between long-term intake of selenium and selenium status, and subjects living in the excess area are more saturated with selenium than anticipated. More than two months of depletion are required to affect urinary excretion of selenium.

Time-resolved measurements with single droplet introduction to investigate space-charge effects in plasma mass spectrometry.

An investigation of the space-charge induced effects of high concentrations of Pb+ matrix ions on Li+ analyte ions in inductively coupled plasma mass spectrometry (ICP-MS) is presented using a vertically oriented mass spectrometer with single droplet introduction. Greater reproducibility and stability in droplet-to-droplet sample introduction using the monodisperse microparticulate injector (MDMI) was achieved with the vertical orientation. Typical variation (%RSD) in the droplet-to-droplet arrival times, and mass spectrometry peak analytical areas are better than 5%. With this precision, a more quantitative description of the space-charge effect on a single cloud of ions is obtained. Both radial and axial space-charge effects were found to occur in the ion beam. Radial effects result in a loss in intensity because of poor transmission or collisions at surfaces within the mass spectrometer. Axial effects modify the kinetic energy distribution of background ion beam components (e.g., 16O+ and 40Ar+) and sampled ion cloud constituents (e.g., 7Li+). However, axial effects do not appear to generate significant broadening of sampled ion clouds within the mass spectrometer. At the point of charge separation and high ion-beam charge density, the ion cloud maxima for Li and Pb are not coincident. This is because of mass dependent diffusion in the ICP as the ion clouds approach the sampling orifice. Space-charge induced ion loss occurs predominantly at a localized region after the Li+ sampled cloud peak maximum. When the Pb concentration in the sample is sufficiently high the 7Li+ sampled signal has a bimodal peak shape. The existence of the dip and its relative location in the bimodal 7Li+ sampled signal suggests that space-charge effects are localized to the region of high charge density occurring just after charge separation.

Quantitative significance of measuring trimethylselenonium in urine for assessing chronically high intakes of selenium in human subjects.

The purpose of the present study was to investigate the effects of Se restriction on the excretion of Se in men who had consumed high levels of this element during their entire lives. With the use of stable isotopes of Se as selenite, the excretion of methylated Se in urine was investigated in Chinese men (n 10) who had habitual chronic high intakes of this element. The relationship between either urine Se or trimethylselenonium (TMSe) to the estimated long-term Se intake was not linear over the entire range of intake, which was also true for the infusion of labelled selenite. A non-linear relationship was also found between urine TMSe and urine Se both for TMSe arising from catabolism of endogenous body Se and that from infused selenite. The data suggest a close precursor-product relationship of urine Se and its TMSe component based on the nearly identical specific activities for these two selenocompounds. Although dimethylselenide in breath was not measured in the present study, combining urinary TMSe with this breath test may be more useful in the assessment of long-term Se status.

Effect of dietary selenium restriction on selected parameters of selenium status in men with high life-long intake.

The influence of selenium (Se) restriction on disposition in plasma and urine fractions of infused (74)Se (selenite) was studied when adult males (Enshi City, Hubei Province, PRC) whose habitual daily Se intake is approximately 480 microg per day were transferred to Lichuan County, where the daily intake is approximately 30 microg. The subjects received an infusion (106 microg Se) on the day before consuming foods low in Se and a second infusion (113 microg Se) 63 days later. Blood and 24-hour urine samples were collected each day for 7 days after the first infusion and on days 22, 43, and 62 following the first infusion. Urine and blood were also collected daily for the next 7 days after the second infusion. Plasma total Se concentration increased for 7 days after each of the two infusions and urine Se decreased exponentially following both the first and second infusions. The excretion of trimethylselenonium followed the same pattern as the total urinary Se. Surprisingly, there was not a significant difference in selenite retention between the two infusion periods, and the data indicated that, regardless of the chemical form of Se present in various organs, its catabolism leading to excretion in urine followed the same pathway as that of selenite. Labeled Se was incorporated predominantly in the plasma selenoprotein P fraction and the half-life of Se in this fraction was determined to be 1.9 to 2.9 days. Thus, a longer depletion period is required in these subjects to obtain more significant changes.

Time-resolved inductively coupled plasma mass spectrometry measurements with individual, monodisperse drop sample introduction.

Individual ion clouds, each produced in the ICP from a single drop of sample, were monitored using time-resolved mass spectrometry and optical emission spectrometry simultaneously. The widths of the ion clouds in the plasma as a function of distance from the point of initial desolvated particle vaporization in the ICP were estimated. The Li(+) cloud width (full width at halfmaximum) varied from 85 to 272 µs at 3 and 10 mm from the apparent vaporization point, respectively. The Sr(+) cloud width varied from 97 to 142 µs at 5 and 10 mm from the apparent vaporization point, respectively. The delays between optical and mass spectrometry signals were used to measure gas velocities in the ICP. The velocity data could then be used to convert ion cloud peak widths in time to cloud sizes in the ICP. Li(+) clouds varied from 2.1 to 6.6 mm (full width at half-maximum) and Sr(+) clouds varied from 2.4 to 3.5 mm at the locations specified above. Diffusion coefficients were estimated from experimental data to be 88, 44, and 24 cm(2)/s for Li(+), Mg(+), and Sr(+), respectively. The flight time of ions from the sampling orifice of the mass spectrometer to the detector were mass dependent and varied from 13 to 21 µs for Mg(+) to 93 to 115 µs for Pb(+).

Time-resolved measurements of individual ion cloud signals to investigate space-charge effects in plasma mass spectrometry.

A new approach to directly monitor space charge induced effects due to high concentrations of efficiently ionized elements in inductively coupled plasma mass spectrometry (ICP-MS) is described. The broadening of ion clouds produced from individual, monodisperse drops of sample is measured by using time-resolved ICP-MS. The extent of broadening due to high concentrations of Pb in the sample is related inversely to the analyte mass. For the lightest analyte investigated, Li(+), the relative width of the time-resolved analyte peak increases and then shows a dip in the center as the Pb concentration is increased to 500 and then 1500 µg/mL. The initial results of experiments that investigated chemical matrix effects as a function of concomitant species concentration, analyte mass, and sampling location in ICP-MS are consistent with space-charge effects.

Inductively coupled plasma mass spectrometry signal fluctuations due to individual aerosol droplets and vaporizing particles.

ICPMS signal fluctuations, in some cases larger than 1 order of magnitude, are observed on a tens of microsecond time scale. The analyte ICPMS signal fluctuations are larger than those characteristic of analyte ion emission intensities observed from the side of the plasma. The analyte, solvent and plasma gas ICPMS signal fluctuations correlate with atom and ion emission intensities monitored 1.3 mm in front of the sampling cone. Analyte and O+ ICPMS signals are depressed near incompletely desolvated droplets and enhanced near vaporizing analyte particles. ICPMS molecular ion signals including ArH+, O2+, H2O+, and H3O+ are enhanced near both incompletely desolvated droplets and vaporizing particles. In contrast to other species, Ar+ ICPMS signals are depressed near a vaporizing particle. The nature of the ICPMS signal fluctuations (spikes or dips) observed at a fixed sampling position (sampling depth) is critically dependent on the center (nebulizer) gas flow rate.

Influence of small amounts of organic solvents in aqueous samples on argon inductively coupled plasma spectrometry.

The presence of organic solvents in aqueous samples in concentrations as low as 0.1% by volume had a large effect on emission and fluorescence signals. Both atom and ion emission signals were depressed when organic solvents were present. In contrast, Sr II fluorescence intensities were enhanced by up to a factor of 3.5 when the sample contained 2% (v/v) organic solvent. More ions were produced when the sample contained organic solvent. However, the fractions of atoms and ions that were excited and emitted light decreased. Ar and H emission intensities can be used as diagnostic signals to warn the operator when plasma conditions have changed due to the presence of organic solvents.

Signal fluctuations due to individual droplets in inductively coupled plasma atomic emission spectrometry.

Large emission intensity fluctuations are observed from analyte species in inductively coupled plasmas. Relative standard deviations are as large as 71% when emission is viewed with time resolution of 10 microseconds. Low in the plasma, peaks in atom emission intensity are accompanied by depressions in ion emission. This behavior appears to be due to local cooling by aerosol droplets. High in the plasma, peaks in atom emission are followed by peaks in ion emission. These emission spikes result from atomization and ionization of analyte from vaporizing particles. Laser light scattering experiments show that droplets or particles exist in a conventional 1.0-kW plasma up to 20 mm above the load coil. Emission signals detected high in the plasma correlate with laser light scattering signals below.