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At least 163 records · Page 9Linked to original sources
PubMed1977

Ultrastructure of leydig cells as revealed by secondary tissue treatment with a ferrocyanide-osmium mixture.

Leydig cells prepared routinely (glutaraldehyde--osmium) for ultrastructural studies are generally found to be lacking in subcellular detail as a result of poor membrane preservation and a dense cytoplasmic matrix. A method modified after that of Karnovsky (1971), utilizing a ferrocyanide--osmium mixture for post-treating glutaraldehyde fixed tissued, was found to yield routinely excellent preservation of Leydig cells. The primary advantages of this method were the enhancement of contrast within the Leydig cell and greatly improved membrane preservation. In addition, the smooth endoplasmic reticulum always appeared as an extensive network of interconnected tubules of uniform diameter; mitochondria, lysosomes, peroxisomes, multivesicular bodies, and Golgi were especially prominent. Glycogen and microfilaments, not readily seen in routine preparations, were found to be abundant in these cells. New observations on the numbers and distributions of subcellular organelles are described and are discussed in relation to their possible role in the steroidogenic process. In view of the greatly improved tissue preservation observed in this study, it is suggested that this treatment be used routinely for preservation of rat Leydig cells.

Animals↗
PubMed1987

Use of osmium tetroxide-potassium ferricyanide in reconstructing cells from serial ultrathin sections.

We describe a technique, modified from Langford and Coggeshall [Anat. Rec., 197 (1980) 297-303; J. Comp. Neurol., 203 (1981) 745-750], for enhancing membrane contrast and defining cellular boundaries, that is useful for reconstructing individual cells from ultrathin sections. The cells of interest in our study were neuronal germinal cells and their differentiated progeny in the retinas of young goldfish. These cells were labeled by pulse injections of [3H]thymidine, and they were subsequently identified in EM autoradiographs by the presence of silver grains overlying their nuclei. In tissue prepared by traditional procedures (fixation in mixed aldehydes, postfixation in osmium tetroxide) it was difficult to follow the processes of these cells through the complex, dense network of cells in the differentiated retina. However, in tissue postfixed with a mixture of osmium tetroxide and potassium ferricyanide, the contrast of the cell membranes was improved and, in favorable preparations, a dense precipitate was formed in the extracellular spaces, serving to outline individual cells. This greatly faciliated the preparation of reconstructions from serial ultrathin sections.

Animals↗
PubMed2006

Methylcytosine-selective fluorescence quenching by osmium complexation.

We report on the control of the emission from a fluorophore fixed on DNA using the methylcytosine-selective addition of an osmium-bipyridine complex. We have synthesized DNA modified by a microenvironment-sensitive fluorophore, 2-dimethylamino-6-acyl-naphthalene. The emission from the fluorophore tethered to a probe DNA was effectively quenched by a methylcytosine glycol-osmium-bipyridine triad, which was located in the immediate neighborhood of the fluorophore. The discrimination of the cytosine methylation status at a methylation hot spot in the p53 gene was also executed using a well-designed fluorescent DNA probe.

Animals↗
PubMed2005

Osmium tetroxide, used in the treatment of arthritic joints, is a fast mimic of superoxide dismutase.

Aqueous solutions of osmium tetroxide (OsO4) have been injected into arthritic knees for the past 45 years to chemically destroy diseased tissue, in a procedure termed "chemical synovectomy." Arthritis is an inflammatory disease. The primary inflammatory chemical species are the superoxide anion radical (O2.-) and nitric oxide (.NO), which combine to form the peroxynitrite anion (ONOO-). Here we show that OsO4 does not react with ONOO- but very efficiently catalyzes the dismutation of O2.- to O2 and H2O2. Using the pulse-radiolysis technique, the catalytic rate constant has been determined to be (1.43+/-0.04) x 10(9) M-1 s-1, independent of the pH in the 5.1-8.7 range. This value is about half that for the natural Cu,Zn-superoxide dismutase (Cu,Zn-SOD). Per unit mass, OsO4 is about 60 times more active than Cu,Zn-SOD. The catalytically active couple is OsVIII/OsVII, OsVIII oxidizing O2.- to O2 with a bimolecular rate constant of k=(2.6+/-0.1)x10(9) M-1 s-1 and OsVII reducing it to H2O2 with a bimolecular rate constant of (1.0+/-0.1)x10(9) M-1 s-1. Although lower valent osmium species are intrinsically poor catalysts, they are activated through oxidation by O2.- to the catalytic OsVIII/OsVII redox couple. The OsVIII/OsVII catalyst is stable to biochemicals other than proteins and peptides comprising histidine, cysteine, and dithiols.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2005

Catalytic effects of ruthenium and osmium spontaneous deposition on platinum surfaces toward methanol oxidation.

The influence of ruthenium and osmium spontaneous deposition on polycrystalline platinum in sulfuric acid was studied by conventional electrochemical techniques. The inhibition of the hydrogen adatom voltammetric profile by the foreign adatoms was used to calculate the degree of surface coverage of ruthenium, osmium, and a mixture of both metal ions from solutions of different composition. Methanol adsorption and oxidation were compared on bare platinum, platinum/ruthenium, platinum/osmium, and ternary compounds, considering the efficiency of methanol oxidation per hydrogen adatom displaced by the foreign metal on platinum.

Adsorption↗
PubMed1976

The reactions of oxo-osmium ligand complexes with isopentenyl adenine and its nucleoside.

We report syntheses of oxo-osmium(VI)bis(ligand) esters of N6-(delta2-isopentenyl) adenine (6-ipAde) and its nucleoside (IPA) which result from the addition of OsO4 to the double bond of the isopentenyl group. A study of the kinetics of these reactions shows that under typical conditions the rates of reaction relative to thymidine are as follows: for OsO4-pyridine: thymidine = 1; 6-ipAde = 4600: for OsO4-2,2'-bipyridyl: thymidine = 380; 6-ipAde = 8600; IPA = 8600. We also report syntheses of osmate esters of IPA in which the osmium is bonded through the 2'-and 3'-hydroxyl groups of the ribose residue.

Adenine↗
PubMed2000

Gold toning preserves integrity of silver enhanced immunogold particles during osmium tetroxide treatment for demonstration of a biogenic amine.

We describe a protocol that enhances immunolabelling of nervous tissue for ultrastructural study. Insect tissue is fixed, sectioned, and labelled with a polyclonal antiserum against serotonin and a secondary antibody conjugated with 1 nm colloidal gold. The gold particles are silver-enhanced to ease detection and then protected by gold toning. Finally, the tissue is post fixed in glutaraldehyde fixative followed by osmium tetroxide and further processed for electron microscopy. We demonstrated on insect nervous tissue that gold toning protects marker particles from the influence of osmium tetroxide. Use of buffered solutions throughout the protocol led to well preserved ultrastructural details, and marker particle size was not reduced with a short gold toning time. We also suggest use of this protocol for vertebrate or other invertebrate tissue.

Animals↗
PubMed2002

Determination of nanogram quantities of osmium-labeled single stranded DNA by differential pulse stripping voltammetry.

Earlier, we showed that using differential pulse cathodic stripping voltammetry with hanging mercury drop electrode (HMDE), single-stranded (ss) DNA modified with osmium tetroxide, pyridine reagent (Os,py) can be determined at concentrations down to about 10-5 ng/ml. Here, we show that by exchanging Os,py for osmium tetroxide, 2,2'-bipyridine (Os,bipy) and decreasing the pH of the background electrolyte from neutrality to about pH 4, ssDNA can be determined at concentrations lower by one order of magnitude. Determination of DNA at such low concentrations may find use in various areas of molecular biology and in biotechnologies, including the development of DNA sensors.

DNA, Single-Stranded↗
PubMed2002

Differential pulse adsorptive stripping voltammetry of osmium-modified peptides.

Complexes of osmium tetroxide with nitrogen ligands were developed and used in our laboratory as probes of the DNA structure. Here, we show that the complex of osmium tetroxide with 2,2'-bipyridine (Os,bipy) can be used for modification and electrochemical detection of proteins at neutral pH. Salmon luteinizing hormone (SLH) containing two tryptophan (Trp) residues and human luteinizing hormone (HLH) containing one Trp were modified by Os,bipy and measured by differential pulse adsorptive stripping voltammetry (DPAdSV) at a hanging mercury drop electrode (HMDE). The intensity of the DPAdSV catalytic signals corresponded to the number of Trp residues in the peptide molecule. Decreasing pH of the background electrolyte from 6.6 to 3.8 led to the increase of DPAdSV signals, suggesting that at pH 3.8, the DPAdSV detection limit might be well below 1 ng/ml. Our results suggest that Os,bipy is potentially useful for chemical modification of proteins.

Adsorption↗
PubMed2000

Covalent attachment of osmium complexes to glucose oxidase and the application of the resulting modified enzyme in an enzyme switch responsive to glucose.

Pyridine-based osmium complexes bearing either a carboxylate or aldehyde group were covalently attached to glucose oxidase and were shown to work as mediators for the reoxidation of the enzyme. For the complex containing the carboxylate group, the binding was made through carbodiimide coupling to the amine residues in the protein. For the complex containing the aldehyde group, the reductive coupling was carried out by condensation with the amino groups on the protein in the presence of sodium cyanoborohydride. Electrochemical studies show evidence for both intramolecular and intermolecular redox mediation for the electrochemical reoxidation of the modified glucose oxidases in the presence of glucose. The modified enzymes adsorbed on glassy carbon and platinum show different electrochemical responses for the two electrode materials, suggesting that orientation of the adsorbed enzyme is induced due to the interaction of the osmium complex with the different surfaces. Construction of enzyme switches based on these modified enzymes was carried out, and their responses were compared with those obtained using native glucose oxidase and a soluble redox mediator.

Aspergillus niger↗
PubMed2005

Platinum group element concentrations and osmium isotopic composition in urban airborne particles from Boston, Massachusetts.

Platinum, Pd, Rh, and Os were found to occur at elevated concentrations in airborne particles (PM10) collected at urban sites in Boston, MA. Average Pt, Pd, Rh, and Os concentrations were 6.9 +/- 1.9, 8.1 +/- 1.8, 1.50 +/- 0.50, and 0.068 (-0.068 + 0.070) pg m(-3), respectively. Elevated Pt, Pd, and Rh concentrations are attributed to automobile catalysts, which use Pt, Pd, and Rh for the removal of pollutants from engine exhaust gas. An automobile catalyst source is supported by significant correlations between these elements and by a Pt/Rh similar to that in catalysts. Elevated Os concentrations are also believed to be the result of emission from automobile catalysts in which Os occurs as an impurity. The isotopic composition of Os (187Os/ 188Os) ranged from 0.30 to 2.90, indicating large variations in Os sources. Osmium has a predominantly anthropogenic origin at concentrations > 0.1 pg m(-3), whereas natural sources are more important at lower Os concentrations. Osmium isotopic composition also indicates that Pt, Pd, and Rh in Boston air are of almost exclusive anthropogenic origin, with a relatively small natural contribution. Our results indicate that scavenging by rain plays a major role in the atmospheric residence time and environmental fate of PGE.

Air Pollutants↗
PubMed2006

Optical sensing of parts per million levels of water in organic solvents using redox-active osmium chromophore-based monolayers.

Optical sensing of parts per million (ppm)-levels of H2O (10-300 ppm) in an organic solvent with robust, osmium chromophore-based monolayers is demonstrated. The H2O-induced reduction of the covalently bound osmium(III) complex is fully reversible and can be readily monitored by UV/vis absorption spectroscopy. The thermally robust sensor can be reactivated chemically within 3 min.

Furans↗
PubMed2001

Effect of meso-substituents on the osmium tetraoxide reaction and pinacol-pinacolone rearrangement of the corresponding vic-dihydroxyporphyrins.

To investigate the effects of electron-donating and electron-withdrawing substituents upon the reaction of porphyrins with osmium tetraoxide, and the pinacol-pinacolone rearrangement of the resulting diols, a series of meso-substituted porphyrins were prepared by total synthesis. Porphyrins with electron-donating substitutents at the meso-positions gave vic-dihydroxychlorins in which the adjacent pyrrole subunit was predominantly oxidized. No such selectivity was observed in a porphyrin containing a methoxycarbonyl as the electron-withdrawing group, whereas a formyl substituent again resulted in oxidation at the pyrrole unit adjacent to the meso-substituent. Under pinacol-pinacolone conditions, vic-dihydroxy chlorins containing 4-methoxyphenyl or 3,5-dimethoxyphenyl groups at the meso-position showed preferential migration of the ethyl group over the methyl group to give 8-ketochlorins, whereas the diol with an n-heptyl substituent under similar reaction conditions gave both 7- and 8-ketochlorins. In contrast, the diol containing a meso-formyl substituent produced the corresponding 7-ketochlorin exclusively. These results indicate that it is not possible to predict the reactivity of meso-substituted porphyrins in the osmium tetraoxide reaction nor the general substituent migratory aptitudes in the pinacol-pinacolone rearrangement based on simple electronic arguments, most likely because many parameters (e.g., meso-beta-pyrrolic steric crowding and long-range electronic effects) ultimately determine the reactivity. The structural assignments of the porphyrin diols and the keto-analogues were confirmed by extensive (1)H NMR studies; some of the dihydroxychlorins and ketochlorins were found to display unusual features in their (1)H NMR spectra.

Alkylation↗
PubMed2002

Examination of the rat eye at the early stage of development with osmium tetroxide staining.

This communication describes the benefit of osmium tetroxide (OsO4) staining on the examination of the eye during the early stage of organogenesis of rat embryos. The embryos were obtained by laparotomy on embryonic day 12 (ED 12) and were stained with OsO4 for examination of the ocular tissues with a binocular stereo-microscope, light microscope and scanning electron microscope. At the binocular stereo-microscopic level, the invaginated lens placode, lens pit and optic cup were clearly distinguished. The osmium-stained lens placode and the optic cup were light brown and dark brown in color, respectively. Light microscopic examination revealed that OsO4 postfixation could provide superior paraffin-embedded embryonic sections. Scanning electron microscopic examination revealed the lens pit as a round opening between the lateral nasal prominence and maxillary prominence. Thus, a rapid technique by which the ocular tissues of rat embryos can be examined under a binocular stereo-microscope was developed. This OsO4 staining method will provide a useful tool for research on organogenesis and ocular development.

Animals↗
PubMed1999

Characteristic intraepidermal nerve fibre endings of the intervibrissal fur in the mystacial pad of the rat: morphological details revealed by intravital methylene blue staining and the zinc iodide-osmium tetroxide technique.

Light microscopic observations employing intravital methylene blue staining and impregnation by the zinc iodide-osmium tetroxide technique are presented for intraepidermal nerve fibre endings of the intervibrissal fur in the mystacial pad of the rat snout. Both procedures revealed anatomical details of the intraepidermal nerve fibre plexus in epidermal hillocks often located very close to the mouths of hairs. These nerve fibres appeared to resemble those described in previous immunohistochemical studies as cluster or bush endings. The methylene blue preparations demonstrated the existence of an intensely stained enlargement at the site of the branching point of the nerve fibres which seemed to be functionally related to the development of such nerve fibre plexuses. Due to their close association with hairs, these nerve fibre plexuses are most likely to be mechanoreceptive. Additionally, solitary varicose nerve fibres were found loosely distributed within the epidermis. The visualisation of 2 different morphological types of nerve fibre endings extends the validity of the concept of punctate sensibility into the epidermis. Methylene blue staining appeared to be somewhat superior to the zinc iodide-osmium tetroxide technique. Due to their selectivity for intraepidermal nerve fibres, the methods applied here supplement immunohistochemical procedures in a helpful manner.

Animals↗
PubMed1988

Organization of the internal membrane system in the principal cells of the mouse epididymis after osmium impregnation.

The ultrastructure of the principal cells of the mouse epididymis was studied using osmium impregnation techniques which have the advantage that the endoplasmic reticulum (ER) content displays a positive reactivity after glutaraldehyde fixation whereas the Golgi condensing vacuoles are negative. In the proximal part (caput) of the epididymis, the Golgi apparatus formed a large supranuclear area filled with electronluscent secretory vacuoles while, in the medial (corpus) and distal (cauda) parts, dictyosomes were small and sparse with few secretory vacuoles. In all the principal cells of the caput, the supranuclear ER cisternae were heterogeneously impregnated. In the corpus and cauda, the ER appeared as an extensive continuous network of canaliculi and saccules which were fenestrated when surrounding mitochondria. The ER content was homogeneously stained but impregnation intensity varied from cell to cell. In the apex of the caput cells, numerous impregnated or electronluscent vesicles were seen in close apposition to the plasma membrane, while in the corpus and cauda some Golgi vacuoles and extensions of ER canaliculi were observed in the terminal webb region. Thus, in the epididymal caput, osmium impregnation suggested that two distinct secretory pathways were functioning continuously. The first corresponded to the transport of proteins to the cell membrane by the Golgi condensing vacuoles. The second might only affect the small impregnated vesicles of the ER, through which proteins bypassed the Golgi apparatus and were exported towards the lumen. In the corpus and cauda, the network organization of the ER and the association of fenestrated cisternae with mitochondria (also found in absorptive epithelial cells) supported the view of a predominant absorptive function in these epididymal parts.

Animals↗
PubMed1966

Rapid release of the zymogen granule protein by osmium tetroxide and its retention during fixation by glutaraldehyde.

Fixation by osmium tetroxide and glutaraldehyde of zymogen granules isolated from rat parotid and pancreas was investigated. Protein determinations showed that osmium tetroxide caused rapid release of most of the soluble protein of the granule during fixation in buffered isotonic sucrose. Such granules when examined in the electron microscope after shadow casting appeared quite flat, indicating that most of the contents had indeed been removed. Numerous damaged membranes of the granules were also observed. In contrast, zymogen granules fixed by glutaraldehyde and shadow cast essentially retained the spherical shape and the protein contents. The application of the shadow-casting technique in quantitative studies on the protein content of zymogen granules is discussed.

Aldehydes↗
PubMed1968

Ultrastructure of human leukocytes after simultaneous fixation with glutaraldehyde and osmium tetroxide and "postfixation" in uranyl acetate.

Human leukocytes in suspension or in monolayer cultures have been processed for electron microscopy by fixation in a freshly made cold mixture of glutaraldehyde and osmium tetroxide and by "postfixation" in uranyl acetate. Simultaneous exposure to glutaraldehyde and osmium tetroxide eliminates many of the shortcomings seen when either of these agents is used alone as the initial fixative. Specimens are processed to the stage of dehydration as single cell suspensions or as very small clumps to assure rapid penetration of fixatives and efficient washing. The technique is rapid and reproducible. Electron micrographs presented in this report illustrate the ultrastructural features of human white cells prepared by this method.

Acetates↗