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  • 1
    ISSN: 0248-4900
    Keywords: SDS-PAGE ; calcium ions ; crude collagenase ; pronase E
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    ISSN: 0016-6480
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0014-5793
    Keywords: Corticotropin ; High-performance liquid chromatography ; Hypothalamus ; Neuropeptide precursor ; Neurophysin ; Tryptic peptide mapping
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0016-6480
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Video images with 2 μs exposures of the Li+ emission in Li pellet ablation clouds have been obtained in a variety of Tokamak Fusion Test Reactor tokamak discharges. The pellet clouds are viewed from behind the pellet, which is injected from the outside midplane. In this view, the emission forms an elongated cigar shape with the long dimension of the cigar aligned with the local magnetic field. In some cases, two distinct parallel cigars can be seen simultaneously, displaced vertically from one another by ∼5 cm. Measurements using a ten channel array of position sensitive photodiodes show that the mean position of the ablation cloud emission can oscillate vertically by ∼4 cm with periods in the 60–100 μs range, and that these oscillations are highly correlated with "bursts'' in the cloud emission. The tilt of the cloud is also measured as a function of time as the pellet traverses the plasma, and in this way the poloidal field profile is obtained. (The total transit time of the pellet is ∼1 ms.) Magnetohydrodynamic equilibrium reconstructions of q profiles have been determined using these measurements.
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  • 6
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new system for routine digitization of video images is presently operating on the Alcator C-Mod tokamak. The PC-based system features high resolution video capture, storage, and retrieval. The captured images are stored temporarily on the PC, but are eventually written to CD. Video is captured from one of five filtered RS-170 CCD cameras at 30 frames per second (fps) with 640×480 pixel resolution. In addition, the system can digitize the output from a filtered Kodak Ektapro EM Digital Camera which captures images at 1000 fps with 239×192 resolution. Present views of this set of cameras include a wide angle and a tangential view of the plasma, two high resolution views of gas puff capillaries embedded in the plasma facing components, and a view of ablating, high speed Li pellets. The system is being used to study (1) the structure and location of visible emissions (including MARFEs) from the main plasma and divertor, (2) asymmetries in gas puff plumes due to flows in the scrape-off layer (SOL), and (3) the tilt and cigar-shaped spatial structure of the Li pellet ablation cloud. © 1997 American Institute of Physics.
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  • 7
    ISSN: 1432-2013
    Keywords: Frosch ; Na- und Ca-Leitfähigkeit ; Membranströme ; Adrenalin ; Frog Atrial Cells ; Na- and Ca-Permeability ; Voltage Clamp ; Adrenalin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Summary 1. The effects of adrenaline on the inward currents flowing through the cardiac membranes were investigated in trabeculae of frog atria, by voltage clamp experiments. TTX was used as an inhibitor of the fast sodium channel and Mn as an inhibitor of a slow calcium-sodium channel. 2. The fact that adrenaline increases the amplitude of the plateau of the cardiac action potentials has been confirmed. This substance does not appreciably modify the current flowing through the fast channel but considerably increases the inward current which, according to previous investigations, is carried by Ca++ and Na+. For this reason, adrenaline can be considered as an activator of the slow channel. The increase of an inward calcium current by adrenaline can partly explain the positive inotropic effect of the substance. 3. Besides increasing the amplitude of the slow response, adrenaline decreases its threshold. This effect can explain that adrenaline is able to restore impaired conduction due to the action of TTX on fast sodium channel, as other workers observed.
    Notes: Zusammenfassung 1. Die Wirkung von Adrenalin auf die durch die Herzmembranen fließenden Einwärtsströme wurde in “voltage-clamp”-Versuchen an Frosch-Vorhofzellen untersucht. Zur Blockierung des schnellen Natrium-Kanals wurde TTX und für den langsamen Calcium-Natrium-Kanal wurden Mn-Ionen verwendet. 2. Hierbei bestätigte sich, daß Adrenalin die Amplitude des Plateaus des Herzaktionspotentials erhöht. Der im schnellen Kanal fließende Strom wird durch Adrenalin nicht merklich verändert, dagegen wird der Einwärtsstrom stark erhöht, der von Ca- und Na-Ionen transportiert wird, wie vorausgehende Untersuchungen gezeigt haben. Adrenalin kann daher als eine den langsamen Kanal aktivierende Substanz betrachtet werden. Die Erhöhung eines Ca-Einwärtsstromes durch Adrenalin kann zum Teil die positive inotrope Wirkung der Substanz erklären. 3. Adrenalin erhöht die Amplitude der langsamen Depolarisation und erniedrigt gleichzeitig deren Schwelle. Diese Wirkung erklärt die Fähigkeit von Adrenalin, eine durch den Einfluß von TTX auf den schnellen Na-Kanal beeinträchtigte Erregungsleitung wiederherzustellen, wie sie von anderen Forschern beobachtet worden ist.
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  • 8
    ISSN: 1432-2013
    Keywords: Heart Muscle ; Ca−Mg Free Solution ; Plateau of the Action Potential ; Slow Inward Current ; Herzmuskel ; Ca−Mg freier Lösungen ; Aktionspotentialplateau ; Langsamer Einwärtsstrom
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Am durchströmten isolierten Herzen der Ratte ergibt die elektrophysiologische Untersuchung der Eigenschaften der Myokardmembran während des Aktionspotentialplateaus und in Abwesenheit zweiwertiger Ionen folgende Resultate: 1. Die Blockierung der Membranpolarisation am Plateau, in der Nähe vonE=0 mV, beruht nicht auf der Beteiligung eines stoffwechselabhängigen aktiven Kaliumresorptionssystems der Zellen. 2. Die Höhe des Plateaus ist von der Natriumaußenkonzentration abhängig, wobei die Membran sich wie eine Natriumelektrode verhält. 3. Dieses Plateau wird durch Tetrodotoxin wenig oder nicht beeinflußt aber durch Mangan unterdrückt. Die unter den gleichen Versuchsbedingungen am Frosch durchgeführten voltageclamp Versuche zeigen, daβ ein langsamer, für die langdauernden Aktionspotentiale verantwortlicher Natriumeinwärtsstrom vorhanden ist, der durch TTX nicht beeinfluβt, durch Mangan jedoch inhibiert werden kann. Ebenso zeigen die bei der Ratte auftretenden langdauernden Natriumpotentiale, die durch TTX nicht beeinfluβt, durch Mangan jedoch inhibiert werden, daβ ein slow-channel ähnlich dem bereits am Frosch beschriebenen vorhanden ist.
    Notes: Summary In isolated perfused rat heart, electrophysiological analysis of myocard membrane properties in the absence of divalent ions during the plateau of the action potential, shows that: 1. The maintenance of the membrane potential at plateau level (nearE=0 mV) does not depend on the action of an active cellular potassium absorption mechanism dependent on metabolism. 2. The plateau potential depends on the external sodium concentration, the membrane behaves like sodium electrode. 3. The plateau potential is little or not at all modified by tetrodotoxine, but totally abolished by manganese ions. A Voltage clamp of frog atrial muscle shows, under identical conditions, the existence of a slow inward sodium current responsible for long duration responses. This current is not modified by tetrodotoxine, but suppressed by manganese ions. So, under similar experimental conditions (Ca++, Mg++, free solution) the existence of long duration sodium responses in the rat proves the existence of a slow channel identical to that previously described in the frog.
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  • 9
    ISSN: 1432-0878
    Keywords: Leydig cells ; Pekin Duck ; Testosterone ; Seasonal cycle ; Ultrastructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Description / Table of Contents: Résumé L'ultrastructure des cellules de Leydig et des cellules de Sertoli du testicule du Canard Pékin a été étudiée au cours de la phase printanière du cycle sexuel, soit de janvier à juillet. Parallèlement on a effectué chez les mêemes animaux la recherche histochimique de la Δ5-3 β-hydroxystéroïdedeshydrogénase (Δ5-3 β-HSDH) ainsi que le dosage, par chromatographie en phase gazeuse des stéroïdes androgènes dans le plasma veineux périphérique et dans le testicule. Les cellules de Leydig du Canard possèdent les organites cytoplasmiques spécifiques des cellules stéroïdogènes (reticulum lisse, mitochondries à crêtes tubulaires) ainsi que d'autres structures souvent rencontrées dans ce type cellulaire (microfilaments, vacuoles, granules denses). Les cellules de Sertoli contiennent un reticulum agranulaire moins développé que celui des cellules de Leydig et, très rarement, des mitochondries à crêtes tubulaires. Ces divers organites cytoplasmiques subissent un cycle saisonnier. La différenciation du reticulum lisse et des crêtes mitochondriales tubulaires commence en janvier et atteint son optimum en mars. Leur régression s'amorce en avril; d'abord accompagnée de structures dégénératives transitoires; elle conduit à la dispartion totale de ces organites en mait. Aucun indice de nécrose n'est observé dans ces cellules. Histochimiquement, une activité Δ5-3 β-HSDH est présente dans les cellules de Leydig et, à un degré moindre, dans les tubes séminifères. Son intensité varie au cours du cycle. La confrontation de l'étude morphologique avec les résultats des dosages hormonaux montre qu'il existe une bonne corrélation entre le développement puis la régression du reticulum lisse et des crêtes tubulaires des mitochondries ainsi que des critères histochimiques de la Δ5-3 β-HSDH d'une part et l'évolution de la testostérone plasmatique et testiculaire d'autre part. De plus on observe une augmentation du rapport testostérone/Δ4-androstènedione testiculaire parallèlement au développement des organites cytoplasmiques. Ces organites semblent donc bien impliqués dans la synthèse et la sécrétion de la testostérone chez le Canard.
    Notes: Summary Leydig and Sertoli cells of the testis of the Pekin duck were studied ultrastructurally during the spring phase of the sexual cycle, from January to July. Simultaneously, in the same animals, Δ5-3 β-hydroxysteroiddehydrogenase (Δ5-3 β-HSDH) activity was ascertained histochemically and androgenic steroids of the plasma and testes were assayed by gas-liquid chromatography. The Leydig cells of the duck possess cytoplasmic organelles specific to steroidogenic cells (smooth reticulum, tubular mitochondria) as well as other structures often found in this cell type (microfilaments, vacuoles, denses bodies). The Sertoli cells contain an agranular reticulum that is less developed than that of the Leydig cells, and rarely show mitochondria with tubular cristae. These various cytoplasmic organelles undergo a seasonal cycle. The differentiation of the smooth reticulum and the mitochondrial tubular cristae begins in January and reaches a maximum in March. They begin to regress in April, at first with transitory degenerative structures, and then by total disappearance of these organelles by May. No indication of necrosis is observed in the cells. Histochemically Δ5-3 β-HSDH activity is present in the Leydig cells, and to a slightly lesser degree in the seminiferous tubules. The intensity varies during the cycle. The comparison of the results of the morphological study with the hormone assays shows that a good correlation exists with the development and regression of the smooth endoplasmic reticulum and tubular cristae in the mitochondria, as well as the histochemical criteria of the Δ5-3 β-HSDH on one hand, and the levels of plasma and testicular testosterone on the other hand. In addition there is an increase in the ratio of testicular testosterone to Δ4-androstenedione which parallels the development of the cytoplasmic organelles. These organelles thus seem to be implicated in the synthesis and secretion of testosterone in the duck.
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  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3431-3434 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Plasma confined by a magnetic dipole is stabilized, at low beta, by magnetic compressibility. The ideal magnetohydrodynamic (MHD) requirements for stability against interchange and high-n ballooning modes are derived at arbitrary beta for a fusion grade laboratory plasma confined by a levitated dipole. A high beta MHD equilibrium is found numerically with a pressure profile near marginal stability for interchange modes, a peak local beta of β∼10, and volume averaged beta of β¯∼0.5. This equilibrium is demonstrated to be ballooning stable on all field lines. © 1999 American Institute of Physics.
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