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  • 11
    Electronic Resource
    Electronic Resource
    A General Sampling Theorem Associated with Differential Operators (1999)
    Springer
    Journal of computational analysis and applications 1 (1999), S. 147-161 
    Details
    ISSN: 1572-9206
    Keywords: Kramer's sampling theorem ; symmetric and self-adjoint operators ; compact resolvents ; Hilbert–Schmidt operators ; Lagrange-type interpolatory series
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract In this paper we prove a general sampling theorem associated with differential operators with compact resolvent. Thus, we are able to recover, through a Lagrange-type interpolatory series, functions defined by means of a linear integral transform. The kernel of this transform is related with the resolvent of the differential operator. Most of the well-known sampling theorems associated with differential operators are shown to be nothing but limit cases of this result.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022625625116
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  • 12
    Electronic Resource
    Electronic Resource
    Analysis of radiation-grafted membranes for fuel cell electrolytes (1992)
    Springer
    Journal of applied electrochemistry 22 (1992), S. 204-214 
    Details
    ISSN: 1572-8838
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology
    Notes: Abstract One of the primary obstacles to be overcome for the development of economical fuel cells is the high cost of the membrane electrolyte. The currently favoured polymer electrolytes consist of poly(tetrafluoroethylene) backbone structures and poly(perfluorosulphonic acid) side chains. In an effort to find lower cost membranes, some radiation-grafted copolymer membranes were investigated. All the membranes contained poly(styrenesulphonic acid) side chains. Three different backbone polymer structures were studied: low-density poly(styrene), poly(tetrafluoroethylene)/poly(perfluoropropylene), and poly(tetrafluoroethylene). The results indicate that the membrane consisting of a poly(tetrafluoroethylene)/poly(styrenesulphonic acid) copolymer is a promising candidate as a fuel-cell electrolyte.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01030179
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  • 13
    Electronic Resource
    Electronic Resource
    Dopamine beta-hydroxylase in human synovial fluid (1977)
    Springer
    Cellular and molecular life sciences 33 (1977), S. 650-652 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Dopamine beta-hydroxylase (DBH) activity has been found in synovial fluid obtained from human knees. The enzyme activity was about 5% of the activity found in the serum of the same control patients. DBH activity in synovial fluid of patients suffering osteoarthritis was 3 times higher.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01946554
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  • 14
    Electronic Resource
    Electronic Resource
    Activation of chromaffin cell Ca 2+ channels by novel dihydropyridine (reply) (1985)
    [s.l.] : Nature Publishing Group
    Nature 313 (1985), S. 504-504 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] GARCIA ET AL. REPLY-We appreciate the interest of Dr H. Glossmann in our letter1 and thank him for his comments. Our paper was intended to show that the novel dihydropyridine BAY-K-8644 (methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4 - (2 - trifluoromethylphenyl) - pyridine-5-carboxylate) activates ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/313504a0
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  • 15
    Electronic Resource
    Electronic Resource
    Effects of the cardiotonic drug ARL-115 on the release of noradrenaline from the cat atrium, the binding of 3H-ouabain to plasma membranes and the movements of calcium in mitochondria (1982)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 320 (1982), S. 255-259 
    Details
    ISSN: 1432-1912
    Keywords: Noradrenaline release ; ARL-115 ; Ouabain binding ; Mitochondrial calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The cardiotonic pyridine derivative ARL-115 increased the spontaneous and electrically-evoked release of 3H-noradrenaline from the cat right atrium superfused with oxygenated Krebs-bicarbonate solution at 37°C. On the contrary, ouabain inhibited the evoked release while it also enhanced the spontaneous release of the transmitter. Vanadate did not affect either spontaneous or evoked release. Tetraethylammonium chloride (TEA) and 4-aminopyridine (4-AP) greatly potentiated 3H-noradrenaline release induced by electrical stimulation; when applied in addition to each agent, ARL-115 failed to further increase the secretory response. 3H-ouabain specific binding to partially purified bovine adrenal medulla plasma membranes was very efficiently antagonized by cold ouabain, but not by vanadate or ARL-115, even at concentrations as high as 10−3 mol/l. 45Ca uptake into isolated bovine adrenal medulla mitochondria was prevented by dinitrophenol (DNP) but unchanged in the presence of ARL-115. 45Ca release from preloaded mitochondria was, again, markedly increased by DNP, but not affected by ARL-115. The results suggest that ARL-115 enhances the release of noradrenaline from cardiac sympathetic nerves by a TEA- and 4-AP-like action. In this manner, ARL-115 would inactivate the K+ current in the nerve terminals, thereby prolonging the duration of the action potential, allowing the Ca2+ channels to remain open longer and more Ca2+ to enter the terminal. ARL-115 is not acting like digitalis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00510137
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  • 16
    Electronic Resource
    Electronic Resource
    Human adrenal chromaffin cell calcium channels: drastic current facilitation in cell clusters, but not in isolated cells (1998)
    Springer
    Pflügers Archiv 436 (1998), S. 696-704 
    Details
    ISSN: 1432-2013
    Keywords: Key words Calcium channels ; Human ; Modulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Human adrenal medullary chromaffin cells were prepared and cultured from a cystic tumoral adrenal gland whose medullary tissue was unaffected. Adrenaline-containing and noradrenaline-containing cells were identified using a confocal fluorescence microscope and antibodies against dopamine beta-hydroxylase (DBH) and phenylethanolamine N-methyltransferase (PNMT). Current/voltage (I/V) curves performed with the voltage-clamped cells bathed in 10 mM Ba2+ (holding potential, V h=–80 mV) revealed the presence of only high-threshold voltage-dependent Ca2+ channels; T-type Ca2+ channels were not seen. By using supramaximal concentrations of selective Ca2+ channel blockers, the whole-cell I Ba could be fractionated into various subcomponents. Thus, I Ba had a 25% fraction sensitive to 1 µM nifedipine (L-type channels), 21% sensitive to 1 µM ω-conotoxin GVIA (N-type channels), and 60% sensitive to 2 µM ω-agatoxin IVA (P/Q-type channels). The activation of I Ba was considerably slowed down, and the peak current was inhibited upon superfusion with 10 µM ATP. The slow activation and peak current blockade were reversed by strong depolarizing pre-pulses to +100 mV (facilitation). A drastic facilitation of I Ba was also observed in voltage-clamped human chromaffin cell surrounded by other unclamped cells; in contrast, in voltage-clamped cells not immersed in a cell cluster, facilitation was scarce. So, facilitation of Ca2+ channels in a voltage-clamped cell seems to depend upon the exocytotic activity of neighbouring unclamped cells, which is markedly increased by Ba2+. It is concluded that human adrenal chromaffin cells mostly express P/Q-types of voltage-dependent Ca2+ channels (60%). L-Type channels and N-type channels are also expressed, but to a considerably minor extent (around 20% each). This dominance of P/Q-type channels in human chromaffin cells clearly contrasts with the relative proportion of each channel type expressed by chromaffin cells of five other animal species studied previously, where the P/Q-type channels accounted for 5–50%. The results also provide strong support for the hypothesis that Ca2+ channels of human chromaffin cells are regulated in an autocrine/paracrine fashion by materials co-secreted with the catecholamines, i.e. ATP and opiates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050691
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  • 17
    Electronic Resource
    Electronic Resource
    Re-evaluation of the P/Q Ca2+ channel components of Ba2+ currents in bovine chromaffin cells superfused with solutions containing low and high Ba2+ concentrations (1996)
    Springer
    Pflügers Archiv 432 (1996), S. 1030-1038 
    Details
    ISSN: 1432-2013
    Keywords: Key words Calcium channels ; Chromaffin cells ; ω-Agatoxin IVA ; ω-Conotoxin ; GVIA ; ω-Conotoxin MVIIC ; Furnidipine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  This study was undertaken to reassess the set of voltage-dependent Ca2+ channel subtypes expressed by bovine adrenal chromaffin cells maintained in primary cultures. Previous views on the pharmacology of such channels had to be revised in the light of the novel data which arose from the use in this study of low and high micromolar concentrations of ω-agatoxin IVA, and low (2 mM) and high (10 mM) concentrations of the charge carrier Ba2+. Whole-cell Ba2+ currents (IBa) through Ca2+ channels were elicited in voltage-clamped chromaffin cells, with a holding potential of –80 mV and depolarising pulses to 0 mV. Mean peak I Ba was 425 pA in 2 mM Ba2+ (59 cells) and 787 pA in 10 mM Ba2+ (42 cells). In 2 mM Ba2+, ω-conotoxin MVIIC (3 μM) inhibited I Ba by 79%; in 10 mM Ba2+, the blockade developed much more slowly and reached only 44%. A low concentration of ω-agatoxin IVA (20 nM) inhibited I Ba by 9%; 2 μM inhibited I Ba by 60%. This blockade was similar in low and high Ba2+ concentrations. After giving furnidipine (3 μM) and ω-conotoxin GVIA (1 μM), 2 μM ω-agatoxin IVA inhibited the remaining current (about 40–45%); this blockade was independent of the Ba2+ concentration. The current could be fully blocked by the cocktail furnidipine/ω-conotoxin GVIA/high ω-agatoxin IVA, both in low and high Ba2+ concentrations. The large Q-type channel component of I Ba is blocked by micromolar concentrations of ω-agatoxin IVA and ω-conotoxin MVIIC. While solutions with a high Ba2+ concentration strongly delayed the development of blockade by ω-conotoxin MVIIC, the blockade by high concentrations of ω-agatoxin IVA was equally effective in solutions with a low or a high Ba2+ concentration. Hence, the use of appropriate Ba2+ and toxin concentrations in this study reveals that P-type Ca2+ channels are poorly expressed in bovine chromaffin cells; in contrast, a robust component of the current depends on Q-type Ca2+ channels. An R-type residual current is not present in these cells.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050231
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  • 18
    Electronic Resource
    Electronic Resource
    Analogies and differences between ω-conotoxins MVIIC and MVIID: binding sites and functions in bovine chromaffin cells (1997)
    Springer
    Pflügers Archiv 435 (1997), S. 55-64 
    Details
    ISSN: 1432-2013
    Keywords: Key words Calcium channels ; Q channels ; Chromaffin cells ; ω-Conotoxin MVIIC ; ω-Conotoxin MVIID ; 45Ca2+ uptake ; Catecholamine release
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The characteristics of the binding sites for the Conus magus toxins ω-conotoxin MVIIC and ω-conotoxin MVIID, as well as their effects on K+-evoked 45Ca2+ entry and whole-cell Ba2+ currents (I Ba), and K+-evoked catecholamine secretion have been studied in bovine adrenal chromaffin cells. Binding of [125I] ω-conotoxin GVIA to bovine adrenal medullary membranes was displaced by ω-conotoxins GVIA, MVIIC and MVIID with IC50 values of around 0.1, 4 and 100 nM, respectively. The reverse was true for the binding of [125I] ω-conotoxin MVIIC, which was displaced by ω-conotoxins MVIIC, MVIID and GVIA with IC50 values of around 30, 80 and 1.200 nM, respectively. The sites recognized by ω-conotoxins MVIIC and MVIID in bovine brain exhibited higher affinities (IC50 values of around 1 nM). Both ω-conotoxin MVIIC and MVIID blocked I Ba by 70–80%; the higher the [Ba2+]o of the extracellular solution the lower the blockade induced by ω-conotoxin MVIIC. This was not the case for ω-conotoxin MVIID; high Ba2+ (10 mM) slowed down the development of blockade but the maximum blockade achieved was similar to that obtained in 2 mM Ba2+. A further difference between the two toxins concerns their reversibility; washout of ω-conotoxin MVIIC did not reverse the blockade of I Ba while in the case of ω-conotoxin MVIID a partial, quick recovery of current was produced. This component was irreversibly blocked by ω-conotoxin GVIA, suggesting that it is associated with N-type Ca2+ channels. Blockade of K+-evoked 45Ca2+ entry produced results which paralleled those obtained by measuring I Ba. Thus, 1 μM of each of ω-conotoxin GVIA and MVIIA inhibited Ca2+ uptake by 25%, while 1 μM of each of ω-conotoxin MVIIC and MVIID caused a 70% blockade. K+-evoked catecholamine secretory responses were not reduced by ω-conotoxin GVIA (1 μM). In contrast, at 1 μM both ω-conotoxin MVIIC and MVIID reduced the exocytotic response by 70%. These data strengthen the previously established conclusion that Q-type Ca2+ channels that contribute to the regulation of secretion and are sensitive to ω-conotoxins MVIIC and MVIID are present in bovine chromaffin cells. These channels, however, seem to possess binding sites for ω-conotoxins MVIIC and MVIID whose characteristics differ considerably from those described to occur in the brain; they might represent a subset of Q-type Ca2+ channels or an entirely new subtype of voltage-dependent high-threshold Ca2+ channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050483
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  • 19
    Electronic Resource
    Electronic Resource
    Q-type Ca2+ channels are located closer to secretory sites than L-type channels: functional evidence in chromaffin cells (1998)
    Springer
    Pflügers Archiv 435 (1998), S. 472-478 
    Details
    ISSN: 1432-2013
    Keywords: Key words Ca2+ channels ; Exocytosis ; Chromaffin cells ; Catecholamine release ; ω-toxins ; Furnidipine ; Lubeluzole
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  This study uses a new strategy to investigate the hypothesis that, of the various Ca2+ channels expressed by a neurosecretory cell, a given channel subtype is coupled more tightly to the exocytotic apparatus than others. The approach is based on the prediction that the degree of inhibition of the secretory response by various Ca2+ channel blockers will differ at low (0.5 mM) and high (5 mM) extracellular Ca2+ concentrations ([Ca2+]o). So, at low [Ca2+]o the K+-evoked catecholamine release from superfused bovine chromaffin cells was depressed 60–70% by 2 μM ω-agatoxin IVA (P/Q-type Ca2+ channel blockade), by 3 μM ω-conotoxin MVIIC (N/P/Q-type Ca2+ channel blockade), or by 3 μM lubeluzole (N/P/Q-type Ca2+ channel blockade); in high [Ca2+]o these blockers inhibited the responses by only 20–35%. At 1–3 μM ω-conotoxin GVIA (N-type Ca2+ channel blockade) or 3 μM furnidipine (L-type Ca2+ channel blockade), secretion was inhibited by 30 and 50%, respectively; such inhibitory effects were similar in low or high [Ca2+]o. Combined furnidipine plus ω-conotoxin MVIIC, ω-agatoxin IVA or ω-conotoxin GVIA exhibited additive blocking effects at both Ca2+ concentrations. The results suggest that Q-type Ca2+ channels are coupled more tightly to exocytotic active sites, as compared to L-type channels. This hypothesis if founded in the fact that external Ca2+ that enters the cell through a Ca2+ channel located near to chromaffin vesicles will saturate the K+ secretory response at both [Ca2+]o, i.e. 0.5 mM and 5 mM. In contrast, Ca2+ ions entering through more distant channels will be sequestered by intracellular buffers and, thus, will not saturate the secretory machinery at lower [Ca2+]o.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050541
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  • 20
    Electronic Resource
    Electronic Resource
    Autocrine/paracrine modulation of calcium channels in bovine chromaffin cells (1998)
    Springer
    Pflügers Archiv 437 (1998), S. 104-113 
    Details
    ISSN: 1432-2013
    Keywords: Key words Calcium channels ; Modulation ; Presynaptic receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Applying 10-s pulses of 10 mM Ba2+ to resting or K+-depolarized (70 mM) bovine adrenal chromaffin cells superfused with a nominal 0Ca2+ solution produced a large catecholamine secretory peak. In contrast, pulses of 10 mM Sr2+ or Ca2+ did not induce secretion from polarized resting cells, and induced smaller and narrower secretory peaks from depolarized cells; the areas of the secretory peaks from depolarized cells were 1.87, 3.06 and 27.4 nA s, respectively, for Ca2+, Sr2+ and Ba2+. Ca2+ channel currents in isolated cells or in cells surrounded by other unpatched cells (cell cluster) were studied with either the continuous-flow or the flow-stop method. When applied to an isolated cell, flow-stop reduced the amplitude of I Ca by 19%, I Sr by 31%, and I Ba by 53%, compared with the current amplitude measured under continuous-flow conditions. This decrease in current amplitude was accompanied by a pronounced slowing down of current activation and could be largely relieved by applying strong depolarizing prepulses (facilitation). Under continuous-flow conditions, 10 µM exogenous ATP reduced (about 50%) I Ca, I Sr and I Ba similarly. On the other hand, the use of Na+ as a charge carrier through Ca2+ channels, or intracellular dialysis with 1 mM BAPTA prevented the modulation of current by flow-stop. In cell clusters, activating secretion from unpatched cells, by either 10 mM Ba2+, 100 µM acetylcholine or 70 mM K+, caused a pronounced slowing down of current activation, as well as a decrease of its magnitude in the voltage-clamped cell immersed in the cluster. Such modulation of isolated cells was not observed. These data are compatible with the idea that the secretory activity of adrenal medullary chromaffin cells ”in situ” controls the activity of their Ca2+ channels through autocrine/paracrine mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004240050754
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