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PubMed1999

Toxicity of chromium to activated sludge.

The work deals with the toxicity of hexavalent and trivalent chromium to activated sludge. Cr(VI) was added as K2Cr2O7, and Cr(III) as Cr2(SO4)3. Toxicity is expressed as the inhibition of respiratory activity of microorganisms present in activated sludge. Respiration was measured by two methods, by means of an oximeter with an oxygen electrode and by means of a manometric apparatus permitting continuous observation of biological oxygen demand (BOD). The equation of the normal distribution function was used to construct inhibition curves and to calculate effective concentration (EC50). The influence of exposure time was observed as was the influence of concentration of activated sludge on the value of EC50. The 1-h EC50 for Cr(VI) by the ISO method was determined to be in the range of 40-90 mg/liter. A greater scatter of measured values, 46-201mg/liter, was found for the first hour of exposure by the manometric method. In the case of Cr(III) only combined inhibition by chromium ions and pH was determined. The 0.5-h EC50 was 49 mg/liter.

Bacteria↗
PubMed1994

Spectroscopic imaging of circular voxels with a two-dimensional Fourier-series window technique.

Spatial localization with the spectroscopic imaging technique is normally implemented with the Fourier-transform approach, yielding rectangular voxels, with potentially significant cross-voxel contamination. Multidimensional Fourier-series window (FSW) is an alternate approach that generates single voxels of predetermined shape, with minimal out-of-voxel contamination. The spatial location of the voxel is shifted by means of postacquisition processing. A two-dimensional circular voxel is introduced, which for many in vivo applications is a good match of the region of interest. Phantom images illustrate the spatial distribution of signal intensity within the circular FSW voxels. Phantom spectroscopic studies show excellent spatial localization, with no detectable out-of-voxel contamination. The circular FSW voxel approach is implemented in human and animal model studies, demonstrating the technique's utility. This arbitrary shape approach can be extended to three dimensions, defining, for example, cylinders, spheres, or ellipsoids.

Adenosine Triphosphate↗
PubMed2006

Macroporous bioactive glass-ceramic scaffolds for tissue engineering.

Highly bioactive scaffolds for tissue engineering were synthesized using a glass belonging to the SiO2-CaO-K2O (SCK) system. The glass SCK was prepared by a traditional melting-quenching route and its bioactivity was assessed by in vitro tests in a simulated body fluid (SBF). The glass was ground and sieved to obtain powders of specific size that were subsequently mixed with polyethylene particles of two different dimensions. The powders were then uniaxially pressed to obtain a crack free green compact that was thermally treated to remove the organic component and to sinter the inorganic phase. The obtained biomaterial was characterised by means of X-ray Diffraction, SEM equipped with EDS, mercury intrusion porosimetry, density measurements, image analysis, mechanical tests and in vitro evaluations. A glass-ceramic macroporous scaffold with a homogenously distributed and highly interconnected porosity was obtained. The amount and size of the introduced porosity could be tailored using various amounts of polyethylene powders of different size.

Biocompatible Materials↗
PubMed1993

The reduction of the inhibitory effect of aluminum on Na+ efflux in barnacle muscles fibers by preinjecting phosphate.

The object of the present study was to test the hypothesis that the pre-enrichment of single muscle fibers from the barnacle Balanus nubilus with inorganic phosphate may protect the basal Na efflux from the inhibitory effect of Al injection. This approach was adopted in the light of evidence that the preinjection of ATP fails to stop the Na efflux in unpoisoned fibers from falling following the injection of Al. The results of the experiments are as follows: (i) Preinjection of K2HPO4 into unpoisoned fibers reduces the magnitude of the inhibitory effect on the basal Na efflux of injected Al in a dose-dependent manner but fails to completely stop it from occurring. (ii) Injection of K2HPO4 following Al into unpoisoned fibers fails to arrest or reverse the inhibitory effect of injected Al. (iii) Injection of K2HPO4 in a concentration as high as 0.5 M is without effect on the course of the basal Na efflux. (iv) Injection of K2HPO4 into ouabain-poisoned fibers fails to stop Al from stimulating the ouabain-insensitive Na efflux. Injection of K2HPO4 following peak stimulation by injecting Al is also without effect. (v) Injection of K2HPO4 in a concentration as high as 0.5 M is without effect on the course of the ouabain-insensitive Na efflux. Collectively, the results obtained with unpoisoned 'hypersensitive' fibers are consistent with the view that a significant fraction of the injected inorganic phosphate binds Al3+, and hence protects the basal Na efflux from the untoward action of Al3+.

Aluminum↗
PubMed1998

A novel crystallization method for visualizing the membrane localization of potassium channels.

The high permeability of K+ channels to monovalent thallium (Tl+) ions and the low solubility of thallium bromide salt were used to develop a simple yet very sensitive approach to the study of membrane localization of potassium channels. K+ channels (Kir1.1, Kir2.1, Kir2.3, Kv2.1), were expressed in Xenopus oocytes and loaded with Br ions by microinjection. Oocytes were then exposed to extracellular thallium. Under conditions favoring influx of Tl+ ions (negative membrane potential under voltage clamp, or high concentration of extracellular Tl+), crystals of TlBr, visible under low-power microscopy, formed under the membrane in places of high density of K+ channels. Crystals were not formed in uninjected oocytes, but were formed in oocytes expressing as little as 5 microS K+ conductance. The number of observed crystals was much lower than the estimated number of functional channels. Based on the pattern of crystal formation, K+ channels appear to be expressed mostly around the point of cRNA injection when injected either into the animal or vegetal hemisphere. In addition to this pseudopolarized distribution of K+ channels due to localized microinjection of cRNA, a naturally polarized (animal/vegetal side) distribution of K+ channels was also frequently observed when K+ channel cRNA was injected at the equator. A second novel "agarose-hemiclamp" technique was developed to permit direct measurements of K+ currents from different hemispheres of oocytes under two-microelectrode voltage clamp. This technique, together with direct patch-clamping of patches of membrane in regions of high crystal density, confirmed that the localization of TlBr crystals corresponded to the localization of functional K+ channels and suggested a clustered organization of functional channels. With appropriate permeant ion/counterion pairs, this approach may be applicable to the visualization of the membrane distribution of any functional ion channel.

Animals↗
PubMed2002

Fluorescence investigation of model compounds for light-emitting alternating copolymers in heterogeneous environments.

In this paper, the fluorescence spectra of the model compounds M(TPA-PPV) and M(TPA-PAV) of novel light-emitting alternating copolymers, were studied and the effect of KNO3 on the interaction between the model compounds and the ionic micelle-water interface was also investigated. The following is found: (i) the fluorescence changes of M(TPA-PPV) are related to the state of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) solution: (ii) an aggregated state can be formed in M(TPA-PAV) solution at low concentration of CTAB; (iii) higher concentrations of KNO3 may affect the interaction between the model compounds and the ionic micelle-water interface.

Air↗
PubMed1984

Mass transport and reaction kinetic parameters determined electrochemically for immobilized glucose oxidase.

Mass-transfer resistances often have pronounced effects on the overall reaction rates of enzymes immobilized at interfaces or in polymeric matrices. In the present work glucose oxidase was immobilized on the surface of a platinum disk electrode by one of three attachment techniques: silane-glutaraldehyde, allylamine-glutaraldehyde, and albumin-glutaraldehyde. In one group of studies the electrodes were rotated, and methods were employed to determine the diffusion and shielding coefficients for transport of a model electroactive compound, i.e., potassium ferrocyanide, through the enzyme matrix. A model electrochemically active compound was used because glucose exhibits a very slow rate of electron transfer at a platinum surface. The diffusion coefficient for ferrocyanide was reduced 7% by the silane-enzyme and 25% by the allylamine-enzyme matrices. In a second group of studies the electrodes were held stationary. Marked internal diffusional resistance was noted for the albumin-glutaraldehyde-enzyme matrix. The calculated flux of ferrocyanide was decreased by a factor of 2000-8500 for transport through albumin-enzyme matrices 0.21-0.063 cm thick, as compared to transport through free solution. In a third group of studies the rotating enzyme-matrix electrode was utilized in determining apparent values of the Michaelis constant for glucose. The velocity of the reaction was determined by amperometric measurement of the concentration of hydrogen peroxide reaching the ring electrode. The results, determined from Eadie-Hofstee type plots of reaction current and substrate concentration, gave values between 12 and 36 mM for the three methods of immobilization.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrochemistry↗
PubMed1991

Cytotoxic action of triphenyltin on mouse thymocytes: a flow-cytometric study using fluorescent dyes for membrane potential and intracellular Ca2+.

Effects of triphenyltin on mouse thymocytes were examined using fluorescent dyes to monitor membrane potential and intracellular Ca2+. Triphenyltin at 3 x 10(-7) M to 1 x 10(-6) M hyperpolarized thymocytes and depolarized them at 3 x 10(-6) M or more, associated with increasing intracellular Ca2+. Hyperpolarization was suppressed by quinine, but not by tetraethylammonium and 4-aminopyridine, suggesting the involvement of Ca(2+)-activated K+ current. Triphentyltin failed to hyperpolarize thymocytes in Ca(2+)-free solution. Results indicate that triphenyltin promotes Ca(2+)-influx to thymocytes. Such an action of triphenyltin may be related to the immunotoxicity of organotins.

4-Aminopyridine↗
PubMed1996

Reaction of ferrate (VI)/ferrate (V) with hydrogen peroxide and superoxide anion--a stopped-flow and premix pulse radiolysis study.

The reduction of ferrate(VI) to ferrate(V) by superoxide ions was studied over the pH range 2.6-13.0 using the premix pulse radiolysis technique. The pH dependence indicates that only the unstable protonated forms of ferrate, H2FeO4 (pKa3.5) and HFeO4- (pKa7.3) are reactive, k(HFeO4(-) + O2) = (1.7 +/- 0.2) x 10(7) M-1 s-1. The stable ferrate ion, FeO4(2-), showed no significant reactivity towards either hydrogen peroxide or superoxide anion. The rate constants for the spontaneous dimerization and decomposition of the protonated ferrates, e.g. k(HFeO4(-) + HFe04) approximately 250 M-1s-1, are orders of magnitude slower than their corresponding reduction reduction by superoxide indicating an outer-sphere mode of electron transfer for the latter process. In contrast the ferrate(VI) species H3FeO4+ (pKa = 1.6 +/- 0.2), H2FeO4, and HFeO4- oxidize hydrogen peroxide, e.g. k(HFeO4(-) + H2O2) = 170 M-1 s-1), at rates which correspond closely to their dimerization rates suggesting an inner-sphere controlled mechanism.

Hydrogen Peroxide↗
PubMed1977

Effect of certain sulphydryl compounds and dimethyl sulphoxide on potassium release by certain amines and proteins from Pseudomonas aeruginosa.

Dithiothreitol, cysteine, and mercapto-ethanol inhibit K+ release from cells of Pseudomonas aeruginosa by amines and NH4Cl incubated at pH 8.5. The inhibitions are competitive for the monamines and NH4Cl but non-competitive for the diamines and spermidine. The percent inhibition is largest for tryptamine, least for spermidine and ethylene diamine. DMSO inhibits K+ release by monamines and certain proteins but not significantly by diamines and histamine. The inhibitions are competitive.

Amines↗
PubMed1999

[The effects of fertilization on yield and root diameter of Codonopsis pilosula var. modesla].

Field trials were conducted using three factors regression design of quadratic orthogonal rotation. The result indicated that under the condition of cultivation, yield and average root diameter of Codonopsis Pilosula var. modesla (Nannf) L.T. Shen showed a positive correlation with N fertilizer application on high fertilization level; The effect of major three fertilizer on yield and average diameter of root was K > P > N. In the course of selective optimization yield which is higher than 3750 kg/hm2 (fresh weight) and average diameter of root which is more than 1.5 cm, the index of fertilizer application for N, P and K pure nutrient is 155 kg/hm2, 250 kg/hm2 (P2O5) and 60 kg/hm2 (K2O) respectively. The ration of N:P:K is 1:1.6:0.4.

Codonopsis↗
PubMed1981

[Determination of the relative RNA-content of liver cell nuclei with gallocyanin-chromealum-staining (author's transl)].

The relative RNA-content of liver cell nuclei from histological slides of rat liver was determined by automatical microscope picture analysis. The slides were stained with Gallocyanin-Chromealum. Extinction measurements are made before and after perchloracid extraction of RNA for the same slide. The changes of extinction measurements caused by the changes of slide thickness and of tissue inhomogeneity could be lowered using this method.

Animals↗