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  • Artikel  (200)
  • Springer  (194)
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  • Artikel  (200)
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  • 1
    Digitale Medien
    Digitale Medien
    Effects of ammonium ions on the depolarization-induced and direct activation of the contractile apparatus in mechanically skinned fast-twitch skeletal muscle fibres of the rat (1996)
    Springer
    Journal of muscle research and cell motility 17 (1996), S. 611-616 
    Details
    ISSN: 1573-2657
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary Mechanically skinned fibre preparations from the extensor digitorum longus muscle of the rat were used to test whether a rise in myoplasmic [NH4 +] in the range 2–10 mm interferes with the mechanism of excitation-contraction coupling in fast-twitch mammalian muscle. Under our conditions (pH 7.10, Mg2+ 1 mm, temperature 23° C), [NH4 +] up to 10 mm had little effect on the Ca+-activated force and on the peak of the t-system depolarization-induced force response. However, the duration of the depolarization-induced force response was decreased significantly at [NH4 +] ≥2 mm. From these data we conclude that the intracellular accumulation of NH4 + is not likely to play a major role in fatigue. Nevertheless, the build up of NH4 + during fatigue, may have a significant inhibitory effect on the force output by decreasing the duration of the t-system depolarization-induced activation of the contractile apparatus.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00154055
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  • 2
    Digitale Medien
    Digitale Medien
    Microfluorometric analyses of glycogen in freshly dissected, single skeletal muscle fibres of the cane toad using a mechanically skinned fibre preparation (1998)
    Springer
    Journal of muscle research and cell motility 19 (1998), S. 631-638 
    Details
    ISSN: 1573-2657
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The main objective of this study was to analyse glycogen in single muscle fibres, using a recently developed microfluorometric method which detects subpicomol amounts of NADPH, glucose and glycogen (as glucosyl units) (detection limit 0.16–0.17pmol in a 25nl sample) without fluorochrome amplification. The fibres were freshly dissected from the twitch region of the iliofibularis muscle of the cane toad (Bufo marinus), and were mechanically skinned under paraffin oil to gain access to the intracellular compartments. The results show that: (1) glycogen concentrations in toad skeletal muscle fibres range between 25.8 and 369mmol glucosyl units/litre fibre volume; (2) there is a large variation in glycogen content between individual fibres from the iliofibularis muscle of one animal; (3) there are seasonal differences in the glycogen content of toad single muscle fibres; (4) the total amount of glycogen in single muscle fibres of the toad does not decrease significantly when storing the tissue, under paraffin oil, at 20–25°C for up to 6h or at 4°C for up to 24h; and (5) 15–26% of fibre glycogen can be washed in an aqueous solution at pH 5–7, within 5min, while 74–85% of fibre glycogen remains associated with the washed skinned fibre, even after 40min exposure of the skinned fibre preparation to the aqueous environment. The retention of most glycogen in the fibre preparation after mechanical removal of the plasma membrane and extensive washing indicates that in toad skeletal muscle fibres the largest proportion of glycogen is tightly bound to intracellular structures. The results also show that the skinned muscle fibre preparation is well suited for microfluorometric glycogen determination, since low molecular weight non-glycogen contributors to the fluorescence signal can be removed from the myoplasmic space prior to the glycogen hydrolysis step.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1023/A:1005377030193
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  • 3
    Digitale Medien
    Digitale Medien
    Theory of the vacuum drying of frozen tissues (1953)
    Springer
    Bulletin of mathematical biology 15 (1953), S. 411-429 
    Details
    ISSN: 1522-9602
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Mathematik
    Notizen: Abstract A general theory of the drying of frozen tissue is developed and applied to the measurement of the drying rate of frozen guinea pig liver. It is shown that for a given temperature of the subliming ice crystals the mininum drying time of a piece of guinea pig liver is greater than the minimum sublimation time of a piece of ice of the same size and shape by a factor of the order of one thousand. This fact has many implications in the design of freeze-dry apparatus which will be developed in a following paper.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02476434
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  • 4
    Digitale Medien
    Digitale Medien
    Aminolaevulinic Acid-induced Photodynamic Therapy in the Treatment of Dysplastic Barrett's Oesophagus and Adenocarcinoma (1999)
    Springer
    Lasers in medical science 14 (1999), S. 278-285 
    Details
    ISSN: 1435-604X
    Schlagwort(e): Keywords: Adenocarcinoma; Aminolaevulinic acid; Barrett's oesophagus; Dysplasia; Photodynamic therapy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Medizin , Physik , Technik allgemein
    Notizen: Abstract . Photodynamic therapy (PDT) may have a role in the prevention of oesophageal cancer. Ten patients with Barrett's oesophagus, three with low-grade dysplasia (LGD), four with high-grade dysplasia (HGD), one with carcinoma in situ and two with invasive carcinoma, were treated with PDT. All received 30 mg/kg aminolaevulinic acid (ALA) followed 4 h later by laser endoscopy. Half were treated with red light (630 nm; 100 mW/cm2 for 1000 s) and half with green light (514 nm; 100 mW/cm2 for 500 s). Columnar epithelial regression was seen in all patients with dysplasia (mean area decrease 44%; range 10–100%), with apparent elimination of dysplasia in all cases. In patients with in situ or invasive carcinoma, no response was seen. ALA-induced PDT, using either red or green light, produces effective ablation of dysplastic Barrett's oesophagus, hence may have a role in the prevention of oesophageal carcinoma, but has little effect on in situ or invasive adenocarcinoma.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s101030050095
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  • 5
    Digitale Medien
    Digitale Medien
    Radiation losses due to discontinuities in asymmetric three-layer optical waveguides (1980)
    Springer
    Optical and quantum electronics 12 (1980), S. 143-158 
    Details
    ISSN: 1572-817X
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract In this paper, the radiation losses caused by film thickness and refractive index discontinuities in asymmetric slab waveguides are examined theoretically. A technique developed by Mahmoud and Beal for dealing with the continuous part of the radiation spectrum is used. Several numerical examples which show the radiation loss for various waveguide configurations are presented and discussed and, where appropriate, comparisons with other related work made. In the case of asymmetric thickness steps, the radiation losses are found to be appreciably higher than those computed for symmetric guides. The radiation losses for guides having the same thickness were found to decrease as the guide thickness increased. Once the TE1 mode become guided, the losses decreased rapidly. However, if the two guides had different thickness then it was found that the losses exhibited a minimum.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00619558
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  • 6
    Digitale Medien
    Digitale Medien
    Alterations in the fraction of oxygen in inspired gas affect rates of renal prostaglandin E2 synthesis in anesthetized dogs (1981)
    Springer
    Cellular and molecular life sciences 37 (1981), S. 1293-1294 
    Details
    ISSN: 1420-9071
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Summary Reductions of oxygen in inspired gas from 20% to 15%, in anesthetized dogs, reduced arterial PO2 and increased the renal efflux of PGE2 but not PGF2a . Renal blood flow, blood pressure, plasma renin activity as well as arterial pH and PCO2 were unaffected. PGs may mediate the renal hemodynamic or excretory consequences of alterations in PO2. In addition, minor variations in PO2 might account, in part, for the variable renal venous PGE2 concentrations reported under basal conditions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01948368
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  • 7
    Digitale Medien
    Digitale Medien
    Mycorrhizae from Denali National Park and Preserve, Alaska (1995)
    Springer
    Mycorrhiza 6 (1995), S. 21-29 
    Details
    ISSN: 1432-1890
    Schlagwort(e): Key words Mycorrhizae ; Arctic-alpine ; Dark septate fungi
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  Roots of 40 taxa of higher plants (Pteridophyta, Spermatophyta) from two alpine study sites in Denali National Park and Preserve in central Alaska were examined for their mycorrhizal colonization. We observed ectomycorrhizae on six species: Betula nana, Salix reticulata, Salix polaris, Salix arctica, Polygonum viviparum, and Dryas octopetala. Seven taxa, Cassiope tetragona, Empetrum nigrum, Ledum palustre subsp. decumbens, Ledum palustre subsp. groenlandicum, Loiseleuria procumbens, Vaccinium uliginosum and Vaccinium vitis–idaea (all Ericales), had ericoid mycorrhizae. One species, Arctostaphylos alpina, formed a typical arbutoid mycorrhiza. Two species (Sibbaldia procumbens and Aconitum delphinifolium) showed well-developed VA mycorrhizae, whereas three species of plants (Lycopodium clavatum, Silene acaulis and Oxytropis scammaniana) had vesicles, but no arbuscules. The roots of 11 other plants (Lycopodium clavatum, Lycopodium selago, Silene acaulis, Gentiana algida, Lupinus arcticus, Oxytropis scammaniana, Pedicularis langsdorffii, Pedicularis capitata, Pedicularis verticillata, Artemisia sp. and Carex bigelowii) had a variety of intracellular colonizations which are referred to as dark septate fungi. No mycorrhizae were found on 12 other plants: Equisetum arvense, Equisetum variegatum, Lycopodium alpinum, Polygonum bistorta, Saxifraga hieracifolia, Saxifraga hirculus, Astragalus alpinus, Pedicularis kanei, Petasites frigidus, Carex podocarpa, Carex microchaeta and Poa arctica. A possible ecological role of dark septate fungi is discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s005720050101
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  • 8
    Digitale Medien
    Digitale Medien
    Elevated concentrations of mercury in mussels (Mytilus californianus) associated with pinniped colonies (1981)
    Springer
    Marine biology 65 (1981), S. 45-48 
    Details
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The geographic distribution of mercury concentrations in the California mussel Mytilus californianus, collected from 1977–1978 at 43 sites along the western coastline of the continental United States is marked by consistently elevated levels at two locations. These two sites, which are relatively isolated from anthropogenic inputs and mercuryrich minerals, both contain large pinniped and marine bird populations. The relatively elevated mercury levels measured in the excrement of a pinniped from one of those locales indicate that the concentrated discharge of mercuryrich waste products from the marine ecosystem's top carnivores is contaminating lower trophic levels.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00397066
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  • 9
    Digitale Medien
    Digitale Medien
    Stable carbon isotope variability in marine macrophytes and its implications for food web studies (1984)
    Springer
    Marine biology 81 (1984), S. 223-230 
    Details
    ISSN: 1432-1793
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract Stable carbon isotope ratios (δ13C) of eelgrass Zostera marina and of kelp Laminaria longicruris showed considerable variation in time and space. The isotopic composition of Z. marina varied seasonally from a mean of-6‰ for leaves formed in June to a mean of-10‰ for leaves formed in February. The maximum range for individual leaves was from-5 to-11.4‰. Once a leaf was fully formed, its isotopic composition appeared not to change. In L. longicruris there was no clear seasonal pattern of variation, but in any given blade there was a spatial pattern of variation, with the thickened central band tending to be least negative and the margins most negative. In one blade the range was from-12 to-20‰. Since this range overlaps values that are found in various other macrophytes and in seston, the value of the stable carbon isotope ratio as a tracer in food webs involving macroalgae is questioned. For Z. marina, in which the values are seasonally predictable, the technique may be useful if interpreted with care. The most probable explanation of variation in the ratios is differential storage of biochemical components of different isotopic compostion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00393216
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  • 10
    Digitale Medien
    Digitale Medien
    Effects of diversity and pattern on relative yields of four michigan first year fallow field plant species (1980)
    Springer
    Oecologia 45 (1980), S. 366-371 
    Details
    ISSN: 1432-1939
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Summary 1. A study was designed to investigate the effects of intra and inter-specific competition on the productivity of single and multi-species stands of plants normally dominant in first year old-field communities of mid-Michigan. The four species used were Amaranthus retroflexus, Chenopodium album, Panicum capillare and Setaria viridis. 2. Specifically, we tested (1) the relationship between diversity and productivity, (2) the effect of arrangement (pattern) of individuals within an array of old-field dominants on yield and (3) the expression of dominance and resultant allocation of yields within mixture arrays of different plant species. In direct contrast to many earlier studies, our experiments were completed in the field under natural conditions. 3. Mean yield of the highest yielding monoculture, Amaranthus, was greater than any of the yields of the mixture plots. 4. Changing the pattern within mixtures had no significant effect on the yields of the mixture plots. Distribution of biomass among the component species followed a geometric pattern similar to that predicted by the niche pre-emption hypothesis (Whittaker, 1965, 1969). Using yield as a criterion, dominance was clearly expressed in the mixture plots. Amaranthus contributed more than 50% of the yield in all of the mixture plots. 5. A relative competitive ability index (RCA) was developed to demonstrate more clearly the intra and interspecific relationships among the species in mixture plots and to “equalize” the inherent weight differential among species. Relative Competitive Ability, from highest to lowest, was Amaranthus, Chenopodium, Setaria and Panicum. 6. The paired species experiment demonstrated that the performance of species in multi-species arrays cannot be predicted from paired competition experiments. 7. In the diversity-yield experiment and the paired-species competitive ability experiment, dicotyledons were clearly superior to monocotyledons.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00540207
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