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  • 1
    Electronic Resource
    Electronic Resource
    Correlation of thermally stimulated luminescence with radio frequency surface resistance of high-temperature superconductors (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 1038-1040 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We recently demonstrated that insulating surface impurity phases in high-temperature superconductors can be detected by thermally stimulated luminescence. Moreover, we suggested that the intensity of luminescence is related to the magnitude of the rf surface resistance. In this work we show that a quantitative correlation exists between these two quantities, and that luminescence can be a very useful technique for estimating rf surface resistance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101724
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  • 2
    Electronic Resource
    Electronic Resource
    The Cope rearrangement of 1,5-dimethylsemibullvalene-2,6- and 3,7-dicarbonitriles in the solid state (1989)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 111 (1989), S. 1512-1513 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00186a064
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  • 3
    Electronic Resource
    Electronic Resource
    Cytoplasmic pH of Dunaliella parva and Dunaliella acidophila as monitored by in vivo 31P-NMR spectroscopy and the DMO method (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 74 (1988), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In connection with investigations of the pH-stat mechanism of the unicellular, halotolerant green algae Dunaliella parva and the acid-resistant species D. acidophila, a comparative study on the in vivo measurement of the cytoplasmic pH of Dunaliella cells was carried out, using the so-called dimethyloxazolidine-2,4-dione (DMO) method (distribution of a weak acid between the cells and the medium) and 31P-NMR spectroscopy. As judged by the effects of the external pH, light, anaerobiosis, nitrogen nutrition, permeable weak acids and bases and of ATPase inhibitors, both methods yield reproducible and in principle similar results, although absolute pH values obtained by the NMR method were always slightly higher than those obtained by the DMO method: 1) D. parva is able to maintain a cytoplasmic pH close to 7.0 at external pH 5–8, whereas D. acidophila maintains a neutral pH even at an external pH of 1. 2) The pH-homeostasis requires ATP. 3) During illumination the cytoplasm and the stroma is alkalized. 4) Anaerobiosis induces reversible acidifications of the cells. The physiological importance of these effects is discussed. Advantages of the NMR method for the assessment of the cytoplasmic pH of D. parva are: 1) Better resolution of kinetic effects. 2) Independence of volume determinations. 3) Information about phosphate, phosphomonoester, nucleotide and polyphosphate contents of the cells. However, the ability of 31P-NMR spectroscopy to monitor pH values in different compartments of cells could not be exploited with Dunaliella cells: Although a light-induced alkalization of the cells was observed, differences in the pH of the cytoplasm and the stroma of illuminated cells could not be detected. The disadvantages of the 31P-NMR method are the low sensitivity in comparison to the DMO method and the requirement for an appropriate calibration matrix. Advantages of the DMO method are the high sensitivity and the possibility of measuring many samples in parallel. Disadvantages of the DMO method are the poor resolution of kinetic effects and the need to know the osmotic volume of the cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1988.tb02013.x
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  • 4
    Electronic Resource
    Electronic Resource
    Estimation ofpA2 values at presynaptic α2-autoreceptors in rabbit and rat brain cortex in the absence of autoinhibition (1989)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 340 (1989), S. 639-647 
    Details
    ISSN: 1432-1912
    Keywords: Presynaptic α2-autoreceptors ; Rabbit brain cortex ; Rat brain cortex ; Noradrenaline release ; pA2 value determination
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary An attempt was made to determinepA2 values of antagonists at the presynaptic, release-inhibiting α2-autoreceptorsof rabbit and rat brain cortex under conditions when there was very little released noradrenaline in the autoreceptor biophase and, hence,pA2 values were not distorted by endogenous autoinhibition. Cortex slices were preincubated with3H-noradrenaline and then superfused and stimulated by trains of 4 pulses delivered at 100 Hz or, in a few cases, by trains of 36 pulses at 3 Hz. The α-adrenoceptor agonists clonidine, noradrenaline, and α-methylnoradren-aline concentration-dependently decreased the stimulation-evoked overflow of tritium. The a-adrenoceptor antagonists yohimbine, rauwolscine and idazoxan did not increase the overflow of tritium elicited by 4 pulses/100 Hz in rabbit brain slices and increased it only slightly in rat brain slices. In contrast, the antagonists increased markedly the overflow at 36 pulses/3 Hz. All antagonists caused parallel shifts to the right of the concentration-response curves of clonidine, noradrenaline, and α-methylnoradrenaline.pA2 values were calculated either from linear regression of log [agonist concentration ratio − 1] on log [antagonist concentration] or from sigmoid curve fitting. The slopes of the linear regression lines were close to unity, and thepA2 values calculated by the two methods agreed well. There was no consistent preferential antagonism of any antagonist to any agonist.pA2 values determined with stimulation by 4 pulses/100 Hz were by 0.53–0.80 log units higher than those determined with stimulation by 36 pulses/3 Hz. ThepA2 values (4 pulses/100 Hz) of yohimbine and rauwolscine in rabbit brain slices (approximately 7.9 and 8.2, respectively), were slightly higher than in rat brain slices (approximately 7.6 and 7.7, respectively), whereas thepA2 value of idazoxan in the rabbit. (about 7.1) was lower than itspA2 value in the rat (about 8.0). The experiments confirm thatpA2 values determined under conditions of autoinhibition are too low. Stimulation with short (30 ms) bursts of pulses permits the estimation ofpA2 values at presynaptic a2-autoreceptors without (rabbit) or almost without (rat) the complication of autoinhibition. The values suggest that α2-adrenoceptors in rabbit brain cortex differ slightly from those in rat brain cortex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00717739
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  • 5
    Electronic Resource
    Electronic Resource
    Transmitter release patterns of noradrenergic, dopaminergic and cholinergic axons in rabbit brain slices during short pulse trains, and the operation of presynaptic autoreceptors (1988)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 338 (1988), S. 632-643 
    Details
    ISSN: 1432-1912
    Keywords: Rabbit brain slices ; Noradrenaline release ; Dopamine release ; Acetylcholine release ; Presynaptic autoreceptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Slices of rabbit brain were field-stimulated either by single electrical pulses or by trains of 4 or 8 pulses at 1 or 100 Hz in order to study transmitter release patterns and the autoinhibition of transmitter release. The slices were preincubated with 3H-noradrenaline (cortex), 3H-dopamine (caudate nucleus) or 3H-choline (caudate nucleus). Slices preincubated with 3 H-noradrenaline were superfused with medium containing desipramine 1 gmol/l. The overflow of tritium elicited by single pulses amounted to 0 .19% of the tritium content of the tissue. The overflow elicited by 4 pulses/1 Hz was similar, whereas that elicited by 4 pulses/100 Hz was 5.1-fold higher. Yohimbine 101000 nmol/l increased up to 2.5-fold the overflow evoked by 4 pulses/1 Hz but did not change the overflow evoked by single pulses or 4 pulses/100 Hz. - Slices preincubated with 3 H-dopamine were superfused with medium containing nomifensine 1 μmol/l. The overflow of tritium elicited by single pulses was 0.39% of the tritium content of the tissue. The overflow elicited by 4 pulses/1 Hz was 1.3-fold and the overflow elicited by 4 pulses/100 Hz 1.4-fold higher. Domperidone 1–100 nmol/l and sulpiride 10–1000 nmol/1 increased up to 2.4-fold the overflow evoked by 4 pulses/ 1 Hz but increased only slightly the overflow evoked by single pulses or 4 pulses/100 Hz. - Slices preincubated with 3 H-choline were superfused either with physostigmine-free medium or with medium containing physostigmine 1 μmol/l. In physostigmine-free medium, atropine did not increase the evoked overflow of tritium at any stimulation condition. In physostigmine-containing medium, the overflow elicited by single pulses was 0.18% of the tritium content of the tissue. The overflow elicited by 8 pulses/1 Hz was 2.0-fold and the overflow elicited by 8 pulses/100 Hz 2.2-fold higher. Atropine 2–200 nmol/1 increased up to 2.4-fold the overflow evoked by 8 pulses/1 Hz but increased only slightly the overflow evoked bysingle pulses or 8 pulses/100 Hz. In physostigmine-free medium, sulpiride 10–1000 nmol/1 did not change the single-pulse-evoked overflow of tritium in the absence but increased it in the presence of nomifensine 1 μmol/l. Single pulses elicit a large release of 3H-noradrenaline, 3H-dopamine and 3H-acetylcholine under the conditions of these experiments. Release elicited by single pulses is not subject to autoinhibition except for a small inhibition by spontaneously released transmitter in the case of dopaminergic and cholinergic axons. When 3 or 7 further pulses follow the first one at intervals of 1 s, they elicit much smaller release. At least a great part of the fall is due to autoreceptor mediated inhibition (for 3H-acetylcholine release in the presence of physostigmine only). When 3 or 7 further pulses follow at intervals of 10 ms, they elicit release that is either similar to that evoked by the first pulse (3H-noradrenaline) or much smaller (3H-dopamine, 3H-acetylcholine). However, the fall is not due to stimulation-dependent, auto-receptor-mediated inhibition; autoinhibition does not develop in these short high-frequency trains. Overall, the results are in accord with the autoreceptor theory. They demonstrate the role of autoinhibition in determining the transmitter release patterns of central noradrenergic, dopaminergic and cholinergic neurones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00165627
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  • 6
    Electronic Resource
    Electronic Resource
    The cytoplasmic pH in photosynthesizing cells of the green alga Chlorella fusca, measured by P-31 NMR spectroscopy (1987)
    Springer
    Archives of microbiology 147 (1987), S. 25-29 
    Details
    ISSN: 1432-072X
    Keywords: Chlorella fusca ; Cyclic photophosphorylation ; Cytoplasmic pH ; Green algae ; P-31 NMR spectroscopy ; Photosynthesis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract P-31 NMR investigations were performed with the green alga Chlorella fusca under anaerobic conditions in the dark and in the light. In spectra of cells in the dark the signal of intracellular, nonvacuolar Pi indicates a pH in its chemical environment of 7.0–7.2. Upon illumination this signal looses intensity and shifts to lower field, corresponding to a pH of 7.7. Further downfield no other signal that could be attributed to a Pi-pool in more alkaline environment was detected. By the use of 2-deoxyglucose-6-phosphate as an indicator of cytoplasmic pH, this Pi-signal was assigned to the cytoplasm. The pH increase in the cytoplasm upon transfer of cells from the dark to the light is the same as that previously observed upon transfer of cells from anaerobic to aerobic conditions. In cells performing only cyclic photophosphorylation the cytoplasmic pH is lower than in photosynthesizing cells but still 0.2 pH units higher than in the cells in the dark. The reasons for the missing of a signal of stromal Pi and for the difference in cytoplasmic pH in photosynthesizing cells and those capable only of cyclic photophosphorylation are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00492900
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  • 7
    Electronic Resource
    Electronic Resource
    Respirational activity of Chlorella fusca monitored by in vivo P-31 NMR (1985)
    Springer
    European biophysics journal 13 (1985), S. 89-97 
    Details
    ISSN: 1432-1017
    Keywords: 31P NMR ; respiration ; polyphosphate ; Chlorella ; intracellular pH
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Energy metabolism during dark respiration of the green alga Chlorella fusca was investigated by 31P NMR spectroscopy. The kinetics of the transition from anaerobic to aerobic conditions (and vice versa) was followed with a temporal resolution of 16 s. This transition is accompanied by a shift of the cytoplasmic pH from 6.8 to 7.4, while the vacuolar pH remains constant. Simultaneously, an increase in the concentration of nucleoside-triphosphates and a decrease in the concentration of cytoplasmic orthophosphate take place, as well as the formation of “mobile” polyphosphates. The concentration of ATP and P i reach steady-state levels within 30 s. Upon the reverse transition, from aerobic to anaerobic conditions, steady-state concentrations are obtained only after 3 min.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00256529
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  • 8
    Electronic Resource
    Electronic Resource
    In vivo P-31 NMR measurements of phosphate metabolism in Platymonas subcordiformis as related to external pH (1987)
    Springer
    European biophysics journal 14 (1987), S. 461-470 
    Details
    ISSN: 1432-1017
    Keywords: 31 P-NMR ; respiration ; photosynthesis ; intracellular pH ; polyphosphate ; pH regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract The phosphate metabolism of Platymonas subcordiformis was investigated by 31P-NMR spectroscopy with special attention on the effect of external pH. Glycolyzing cells and cells energized by respiration or photosynthesis gave spectra dependent upon their metabolic state. The transition from deenergized to energized states is accompanied by a shift of cytoplasmic pH from 7.1–7.4, an increase of ATP level and-in well energized cells-the appearance of a new signal tentatively assigned to phosphoarginine. The spectra remain stable over a wide range of external pH. Cytoplasmic pH is well regulated in respiring cells for external pH in the range 5.3–12.3. The typical 0.4 units difference of internal pH in energized as compared to deenergized cells is not affected by external pH in the range 6–12. The intensity of a signal attributed to PEP is markedly increased at high external pH. pH regulation is less efficient below external pH of 6 in deenergized cells. Below pH 3.8 oxidative phosphorylation ceases. Upon raising cytoplasmic pH to 7.4 in deenergized cells polyphosphate chains start to disintegrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00293255
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  • 9
    Electronic Resource
    Electronic Resource
    Distribution of polyphosphates in cell-compartments of Chlorella fusca as measured by 31P-NMR-spectroscopy (1986)
    Springer
    Archives of microbiology 144 (1986), S. 48-54 
    Details
    ISSN: 1432-072X
    Keywords: Chlorella fusca ; Green alga ; 31P-NMR-spectroscopy ; Polyphosphates ; Cellular localization ; Metal-ion complexation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In suspensions of the green alga Chlorella fusca the influence of high pH and high ethylene-diamine-tetraacetic acid concentrations in the external medium, of French-press and perchloric acid extraction of the cells and of alkalization of the intracellular pH on the polyphosphate signal in 31P-nuclear magnetic resonance (31P NMR) spectra was investigated. The results show that part of the polyphosphates of asynchronous Chlorella cells are located outside the cytoplasmic membrane and complexed with divalent metal-ions. These polyphosphates are tightly bound to the cell wall and/or the cytoplasmic membrane and are not susceptible to hydrolyzation by strong acid at room temperature, in contrast to the intracytoplasmic polyphosphates. Upon alkalization of the internal pH of Chlorella cells, polyphosphates, previously not visible in the spectra become detectable by 31P-NMR-spectroscopy. 31P-NMR spectroscopic monitoring of polyphosphates during gradual alkalization of the extra-and intracellular space is proposed as a quick method for the estimation of the cellular polyphosphate content and distribution.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00454955
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  • 10
    Electronic Resource
    Electronic Resource
    P-31 in-vivo NMR investigation on the function of polyphosphates as phosphate-and energysource during the regreening of the green alga Chlorella fusca (1989)
    Springer
    Archives of microbiology 152 (1989), S. 167-171 
    Details
    ISSN: 1432-072X
    Keywords: Chlorella fusca ; Green alga ; Nitrogen starvation ; Polyphosphates ; P-31 in-vivo NMR spectroscopy ; Regreening
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The green alga Chlorella fusca accumulates polyphosphates under conditions of nitrogen starvation while deassembling the photosynthetic apparatus. The polyphosphate content of cells regreening after resupply with nitrate under different culture conditions was investigated by P-31 in-vivo NMR spectroscopy. Neither phosphate deficiency nor anaerobiosis during the first hours of regreening inhibited the recovery of the cells. Polyphosphates were degraded during regeening. Differences in the amount of polyphosphates of phosphate supplied and deficient cells occurred only after more then 8 h. After 16 h phosphate deficient cells had still 75% of the polyphosphate content of phosphate suppled cells. In cells kept under anaerobic conditions polyphosphate degradation was much higher than in oxygen supplied cells. After 8 h they contained less than 50% of the polyphosphate content of oxygen supplied cells. These data suggest that polyphosphates serve as obligatory phosphate source during regreening and may be used as an energy source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00456096
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