Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “OSMIUM”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 73 records · Page 4Linked to original sources
PubMed1984

Osmium tetroxide: a new probe for site-specific distortions in supercoiled DNAs.

Supercoiled plasmids Col E1 and cDm 506 (a Col E1 derivative carrying the D. melanogaster histone gene repeat) were treated with OsO4 in presence of pyridine and the reaction products were analyzed using different approaches. Gel electrophoresis showed that OsO4 binding to supercoiled DNA induced its relaxation without nicking. The amount of osmium bound to DNA (as determined electrochemically) increased with the extent of DNA relaxation. As a result of osmium modification of supercoiled cDm 506, a single denaturation "bubble" was observed in the electron microscope. Mapping of the osmium binding site by S1 nuclease cleavage followed by restriction enzyme digestion has revealed one major site in the intergenic spacer between the H1 and H3 histone genes of D. melanogaster. This site differs from the site cleaved by S1 nuclease in supercoiled DNA in the absence of osmium.

Animals↗
PubMed1985

Osmium impregnation of the endoplasmic reticulum correlates with the functional status of prostatic secretory cells.

The ultrastructure of prostatic secretory cells was studied with the osmium impregnation technique in order to determine if the ER reactivity, or its absence, and its three-dimensional organization correspond to specific functions possibly hormono-dependent. Thick sections (0.3 micron) of rat ventral prostate were made after a five-day impregnation with osmium tetroxide and examined by standard transmission electron microscopy at 80 kV. Studies were performed in normal adult rats, between the 3rd and 26th day following castration and in castrated rats treated with 5-alpha-dihydrotestosterone. In normal rats the impregnation technique delineated three secretory cell types (dark, greyish and clear), representing various degrees of reactivity in ER cisternae; however, despite this quantitative variation, they had similar morphological characteristics. In a longitudinal section, the ER network appeared to be made of saccules running parallel along the length of the cell and forming whorl-like patterns around the nucleus. Comparison of sections taken at various angles suggests that the ER network is made of concentric parallel saccules extending from the base to the apex of the cell and encircling the nucleus and the Golgi apparatus like a large multilayered cylinder. Whereas in dark cells the Golgi apparatus contained mostly clear vesicles, it was always heavily impregnated in clear cells. Noteworthy, osmium deposits were rarely observed on the nuclear envelope of secretory cells but were always present in basal cells. After castration, secretory cells became progressively cubic and the most conspicuous cytoplasmic change was observed in association with the ER. The Golgi apparatus decreased markedly in volume and became heavily stained with metallic osmium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Rapid primary microwave-osmium fixation. I. Preservation of structure for electron microscopy in seconds.

Microwave irradiation (MWIr) of tissues immersed in aldehydes has been used to preserve fine structure in seconds. The purpose of this study was to extend these findings to include rapid primary osmium fixation in a microwave (MW) device with a high volume exhaust. Blocks of rat heart and liver were trimmed to approximately 4 mm3 and exposed to 0.2 M symcollidine-buffered 2% osmium tetroxide for a period of 6-7 sec during MWIr (final solution temperature approximately 45 degrees C). We also evaluated rapid fixation of tissues exposed to MWIr simultaneously with immersion in dilute Karnovsky's fixative (6-7 sec to approximately 50 degrees C) followed by MWIr of specimens immersed in osmium (7 sec to approximately 45 degrees C). Tissues were stored in 0.1 M sodium cacodylate buffer (pH 7.3, 4 degrees C) up to 2 weeks and were stained en bloc in uranyl acetate, dehydrated in a graded series of alcohols, and embedded in propylene oxide-Epon sequence. Thin sections were stained with lead citrate and examined by transmission electron microscopy. We demonstrate that fine structural preservation of tissue blocks can be achieved by MWIr in aldehyde and/or osmium in seconds.

Animals↗
PubMed1987

Lysine-mediated tissue osmication in combination with a tannin-osmium conductive staining method for non-coated scanning electron microscopy of biological specimens.

Glutaraldehyde fixed rat kidney blocks showed no charging effect when treated with lysine and osmic acid and viewed in a scanning electron microscope using an acceleration voltage of 5-30 kV and a specimen current of 1 X 10(-10) A. The podocyte processes and endothelial micropores of the glomerulus were visible without metal coating. Glutaraldehyde fixed, tannin-osmium impregnated and lysine-osmium treated specimens also showed no charging effect in the scanning electron microscope, yielding instead much clearer scanning images which were comparable to those obtained from gold-coated specimens or from tannin-osmium-thiocarbohydrazide-osmium impregnated specimens (Murakami and Jones, 1980).

Animals↗
PubMedDate not supplied

Application of the thiocarbohydrazide-osmium coating technique to scanning electron microscopy of the inner ear.

The application of the thiocarbohydrazide-osmium coating technique to scanning electron microscopy of the inner ear is described. In this procedure specimens which have been prepared for electron microscopy (fixation in buffered glutaraldehyde or in Karnovsky's fixative followed by post fixation in osmium tetroxide) are twice exposed to solutions of thiocarbohydrazide and osmium tetroxide with water rinses in between each treatment. This method binds osmium to the specimen and so eliminates the need to coat the surface of the material with a layer of heavy metal. Initial observations indicate that this is a convenient and reliable method which is capable of yielding good results.

Animals↗
PubMed1988

Increase in the calcium content of cardiac tissue after postfixation with osmium tetroxide.

The concentration of osmium has been measured by destructive chemical analysis in glutaraldehyde fixed heart tissue postfixed with osmium tetroxide and embedded in epoxy resin. After such treatment, the mean atomic number of the specimen (Z) is close to 10, which permits a quantitative analysis of calcium (Ca) by the continuum method, using Z2/A as a correcting factor (A: atomic weight). Wavelength-dispersive X-ray microanalysis has been used to determine the Ca concentration of frog cardiac tissue fixed in glutaraldehyde and embedded in resin. These measurements have been repeated on tissue postfixed in osmium tetroxide; contrary to expectations, the apparent Ca concentration is much higher in osmium treated than in nontreated tissue. However, this result is observed with OsO4 solutions prepared in glass, not with solutions prepared in plastic. It is shown by energy dispersive X-ray analysis of droplets that OsO4 solutions prepared in glass contain large amounts of calcium, potassium and silicon. Care must be taken in preparing OsO4 fixatives when the fixed tissues are to be subjected to X-ray microanalysis of such elements as Ca or Si.

Animals↗
PubMed1978

[Analysis of the mechanism of the fixation of membrane structures using osmium tetroxide. II. An electron microscopic and x-ray structural study of myelin frozen and lyophilized at low temperature].

Comparative electron microscope and X-ray studies were made on the frog sciatic nerve myelin after freeze-drying technique. The specimens were fixed with OsO4 before and after freeze-drying. In the latter case, osmium was used as a hydrophobic solution (OsO4 in CCl4), or in the high vacuum during osmium sublimation. The results obtained in this study do not fit in the accepted mechanism operating during osmium fixation of membranes. Another mechanism is proposed by the authors, and the problem of osmium localization within the space of the myelin repeated unit is discussed.

Animals↗
PubMed1975

Light dependence of osmium reactivity in mouse photoreceptor cells.

Mouse photoreceptor cells exhibit local accumulations of osmium deposits after prolonged osmic staining at slightly elevated temperatures. Deposits were evident along the membranes of outer segment lamellae, Golgi cisternae and vesicles, nuclear envelopes, and synaptic vesicles. Other membranes within the photoreceptor cells were unreactive. No osmium reactivity was seen in other cells of the retina except for osmiophilic outer segment material which had been phagocytized by the pigment epithelium. In the outer segments, inner segments, and synaptic regions of the photoreceptor cells, the amount of osmium reactivity was increased by light stimulation and decreased following extended dark adaptation. The possible significance of the localized osmium reactivity is discussed.

Animals↗
PubMed1986

High-resolution scanning-electron microscopy of stereocilia using the osmium-thiocarbohydrazide coating technique.

Further observations on the detailed morphology of stereocilia have been made using high-resolution scanning-electron microscopy of osmium-thiocarbohydrazide-coated guinea pig cochleae. Three types of cross-link have been observed between stereocilia. Side-to-side and row-to-row linkages are composed of a filamentous network whilst upward-pointing links are a fine single strand, often with a terminal widening. The stereocilia have rough surfaces. These features are observed on both inner and outer hair cells despite reported sensitivity to long periods of osmium fixation. We suggest that osmium sensitivity may be altered by the buffering conditions used during preparation. The observations on osmium-coated material correspond more closely with those made using transmission-electron microscopy than those made using other scanning-electron microscopical preparation techniques, since gold-coating artefacts are absent and the degree of specimen collapse is less. This has enabled us to observe fine details of the links and their attachments which have not been reported previously in SEM.

Animals↗
PubMed1976

Osmium (VI) complexes of the 3', 5'-dinucleoside monophosphates, ApU and UpA.

The dinucleoside monophosphates, ApU and UpA, react with potassium osmate (VI) and 2,2'-bipyridyl to form the corresponding oxo-osmium (VI) bipyridyl sugar ester in which the osmate group is bonded to the terminal 2',3'-glycol. Osmium (VIII) tetroxide and 2,2'-bipyridyl react with the dinucleosides to form the corresponding oxo-osmium (VI) bipyridyl heterocyclic esters which result from addition of the tetroxide to the 5,6-double bond of the uracil residue. Although capable of transesterification reactions, these heterocyclic esters are exceptionally stable toward exchange reactions in solution. No apparent exchange was observed after 1 month. This reaction thus seems promising for single-site osmium labeling in polynucleotides.

Adenine Nucleotides↗
PubMed2005

Isotopic signature and impact of car catalysts on the anthropogenic osmium budget.

Higher osmium concentrations and lower 187Os/188Os ratios in sediments from urban areas have been linked to anthropogenic osmium sources. Automobile catalytic converters that use platinum group metals (PGM) are a potential source for this Os pollution. We present the first direct Os concentrations and isotopic measurements of catalytic converters for major automobile brands to test the assumption that car catalysts release Os with a distinct signature in the environment. The analysis of four new catalytic converters yields similar low 187Os/188Os ratios (0.1-0.2), suggesting a similar source for the PGM. The Os concentrations measured are in the ppt range (6-228 ppt). From our results, the osmium contribution of the car catalysts to the environment through attrition (wearing and grinding down of the catalyst by friction) is predicted to be low, <0.2 pg Os/m2/year in highly urbanized environment. We show that Os loss from catalysts as volatile OsO4 is important at car catalyst operating temperatures. Moreover, we estimate that car catalysts may be responsible for up to approximately 120 pg Os/m2 deposited per year in urban areas and that part of it may be exported to sedimentary sinks. Car catalytic converters are thus an important anthropogenic osmium source in densely populated areas. The NIST car catalyst standard (SRM-2557, made from recycled used catalysts) yields higher concentrations (up to 721 ppt Os) and a more radiogenic isotopic composition (approximately 0.38), perhaps indicative of Os contamination during its preparation.

Automobiles↗
PubMed1967

Oxidation of pyrimidine nucleosides and nucleotides by osmium tetroxide.

1. Pyrimidine nucleosides such as thymidine, uridine or cytidine are oxidized readily at 0 degrees by osmium tetroxide in ammonium chloride buffer. There is virtually no oxidation in bicarbonate buffer of similar pH. Oxidation of 1-methyluracil yields 5,6-dihydro-4,5,6-trihydroxy-1-methyl-2-pyrimidone. 2. Osmium tetroxide and ammonia react reversibly in aqueous solution to form a yellow 1:1 complex, probably OsO(3)NH. A second molecule of ammonia must be involved in the oxidation of UMP since the rate of this reaction is approximately proportional to the square of the concentration of unprotonated ammonia. 3. 4-Thiouridine reacts with osmium tetroxide much more rapidly than does uridine. The changes of absorption spectra are different in sodium bicarbonate buffer and in ammonium chloride buffer. They occur faster in the latter buffer and, under suitable conditions, cytidine is a major product. 4. Polyuridylic acid is oxidized readily by ammoniacal osmium tetroxide, but its oxidation is inhibited by polyadenylic acid. Pyrimidines of yeast amino acid-transfer RNA are oxidized more slowly than the corresponding mononucleosides, especially the thymine residues. Appreciable oxidation can occur without change of sedimentation coefficient.

Chromatography↗
PubMed2002

High-resolution scanning electron microscopy of immunogold-labelled cells by the use of thin plasma coating of osmium.

The feasibility of plasma coating of a thin osmium layer for high-resolution immuno-scanning electron microscopy of cell surfaces was tested, using Drosophila embryonic motor neurones as a model system. The neuro-muscular preparations were fixed with formaldehyde and labelled with a neurone-specific antibody and 10 or 5 nm colloidal gold-conjugated secondary antibodies. The specimens were post-fixed with osmium tetroxide and freeze-dried. Then they were coated with a 1-2 nm thick layer of osmium using a hollow cathode plasma coater. The thin and continuous coating of amorphous osmium gave good signals of gold particles and fine surface structures of neurites in backscattered electron images simultaneously. This method makes it possible to visualize the antigen distribution and the three-dimensionally complex surface structures of cellular processes with a resolution of several nanometres.

Animals↗
PubMed2001

Traumatic osmium tetroxide inoculation.

Osmium tetroxide is a highly oxidizing, corrosive compound commonly found in electron microscopy laboratories. Although osmium tetroxide is known to cause rapid damage to organic tissue, its cutaneous effects have not been well studied. We report a case of traumatic inoculation from a broken vial of 4% osmium tetroxide. Electron microscopy and energy dispersive x-ray spectroscopy confirmed the presence of osmium in the tissue specimen. The lesion was treated by simple excision.

Accidents↗
PubMed1963

Contrast between osmium-fixed and permanganate-fixed toad spinal ganglia.

Chains of vesicles are prominent near the plasma membranes of both the neurons and satellite cells of osmium-fixed toad spinal ganglia. In permanganate-fixed specimens, however, such vesicles are absent, and in their place are continuous invaginations of the plasma membranes of these cells. The discrepancy suggests that the serried vesicles seen in osmium-fixed preparations arise through disintegration of plasma membrane invaginations, and do not represent active pinocytosis, as has been suggested previously. A second difference between ganglia fixed by these two methods is that rows of small, disconnected cytoplasmic globules occur in the sheaths of permanganate-fixed ganglia, but not in osmium-fixed samples. It is suggested that these globules arise from the breakdown of thin sheets of satellite cell cytoplasm which occur as continuous lamellae in osmium-fixed specimens. Possible mechanisms of these membrane reorganizations, and the relevance of these findings to other tissues, are discussed.

Cell Membrane↗
PubMed1974

Pattern of osmium deposition in the parietal cells of the stomach.

Parietal cells of the stomach of the hamster show extensive amounts of dense material in a variety of organelles after prolonged exposure to a solution of osmium tetroxide. Conspicuous amounts of reduced osmium compounds are evident within the granular endoplasmic reticulum, perinuclear cisterna, and vesicular elements of the Golgi complex. Dense material is also apparent within cristae of the mitochondria, the surface coat of the microvilli of the intracellular canaliculus, and vesicular elements of the multivesicular bodies. Multivesicular bodies, containing numerous small osmiophilic elements, are often seen surrounding and/or in close contact with mitochondria. The proximity of the multivesicular bodies to the mitochondria appears to be related to an autophagic process involving degradation of mitochondria. The distribution and intensity of the precipitates within the organelles of the parietal cells vary in different regions of the gastric glands. The findings of this study emphasize that cell structures other than the Golgi complex may contain large concentrations of reduced osmium compounds after prolonged exposure to a solution of osmium tetroxide.

Animals↗
PubMed1998

Scanning electron microscopic observation of the epidermal basement membrane with osmium conductive metal coating.

Osmium conductive metal coating was performed for the scanning electron microscopic observation of the epidermal basement membrane. An extremely thin osmium coating induced the equivalent electrical conductivity as that of a thick platinum coating. As a result, by this coating, the resolution was only nominally reduced. The meshwork structure of the lamina densa and the three-dimensional morphology of the anchoring fibrils were observed in detail. Scanning electron microscopic observation of the osmium-coated specimen coincided with that of the transmission electron microscopic observations. It was evident that the osmium conductive metal coating is much more advantageous than the other coatings for obtaining high resolution images on the observations of the fine structures, such as the epidermal basement membrane.

Animals↗
PubMed1995

Osmium tetroxide and ruthenium tetroxide are complementary reagents for the preparation of epidermal samples for transmission electron microscopy.

Ruthenium tetroxide and osmium tetroxide were compared as post-fixatives in the preparation of human epidermis for transmission electron microscopic examination. Both reagents revealed characteristic lamellar granules within the granular layer and extruded lamellar granule contents in the upper granular layer. The transformation of the granule contents into multilamellar sheets at the interface between the granular and cornified layers and the persistence of these sheets through all levels of the stratum corneum were demonstrated only with ruthenium tetroxide fixation. Therefore, the reactivity of osmium tetroxide with isolated epidermal lipids was examined. The failure of osmium tetroxide to reveal membrane structures in the stratum corneum can be explained by its inability to react with many of the lipid components of these membranes, rather than to selective removal of lipids during tissue processing, as was formerly believed. Ruthenium tetroxide, a stronger oxidizing agent than osmium tetroxide, overcomes this problem but has other severe limitations as a post-fixative.

Fixatives↗