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  • 1
    Electronic Resource
    Electronic Resource
    REPLY FROM M.C. GARCIA, M. G. LOPEZ, A. G. GARCIA, AND M. SANCHEZ CRESPO (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 60 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb13436.x
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  • 2
    Electronic Resource
    Electronic Resource
    A Dihydropyridine-Resistant Component in the Rat Adrenal Secretory Response to Splanchnic Nerve Stimulation (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 58 (1992), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: A study of the effects of dihydropyridine Ca2+ channel modulators on the release of catecholamines from perfused rat adrenal glands, evoked by electrical stimulation of their splanchnic nerves, is presented. Electrically mediated secretory responses were compared to chemically mediated responses (exogenous acetylcholine, nicotine, or high K+). Intensities of stimuli were selected to produce quantitatively similar secretory responses (between 100 and 200 ng per stimulus). The main finding of the study is that responses to transmural stimulation (300 pulses at 1 or 10 Hz) and to acetylcholine were inhibited only partially (about 50%) by isradipine, an L-type Ca2+ channel blocker. In contrast, responses to high K+ (17.5 mM for 2 min) were highly sensitive to isradipine (IC50= 8.2 nM). Responses to nicotine were also fully inhibited by this drug. Bay K 8644 (an L-type Ca2+ channel activator) potentiated mildly the secretory responses to electrical stimulation at 10 Hz and to acetylcholine, but increased threefold the responses to K+ and nicotine. It is, therefore, likely that responses mediated by high K+ or nicotinic receptors are triggered by external Ca2+ gaining access to the internal secretory machinery through L-type, dihydropyridine-sensitive voltage-dependent Ca2+ channels. However, in addition to nicotinic receptors, the physiological stimulation of adrenal medulla chromaffin cells through splanchnic nerves has other components, i.e., muscarinic receptor stimulation or the release of cotransmitters such as vasoactive intestinal polypeptide. The poorer sensitivity to dihydropyridines of secretory responses triggered by electrical stimulation of splanchnic nerve terminals or exogenous acetylcholine speaks in favor of alternative Ca2+ pathways, probably some dihydropyri-dine-resistant Ca2+ channels, in modulating the physiological adrenal catecholamine secretory process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1992.tb10956.x
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  • 3
    Electronic Resource
    Electronic Resource
    Characterization of a Dopaminergic Receptor that Modulates Adrenomedullary Catecholamine Release (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 47 (1986), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Nicotine evokes the release of catecholamines from bovine adrenal glands perfused with oxygenated Krebs-bicarbonate solution. Two 2-min pulses of 5 μM nicotine, at 40-min intervals (S1 and S2), gave net catecholamine outputs of 45.2 ± 3.6 and 29.1 ± 3.5 μg/8 min, respectively. Apomorphine (1 or 10 μM) markedly inhibited catecholamine release during S2 to 9.1 ± 2.2 and 0.5 μg/8 min, respectively. Haloperidol (0.5 μM) reversed the inhibitory effects of apomorphine. Haloperidol alone enhanced catecholamine release induced by nicotine to 67.9 ± 7.9 μg/8 min. [3H]Spiperone binds to adrenomedullary membranes with a KD of 0.24 nM and a Bmax of 117 fmol/mg of protein. Whereas spiperone and haloperidol potently displaced such binding, 3,4-dihydroxyphenylethylamine (dopamine) and sulpiride were poorer displacers, and SCH23390, prazosin, phenoxybenzamine, propranolol, BAY-K-8644, and nitrendipine did not displace [3H]spiperone bound. These data strongly suggest that, as in the cat, the bovine adrenal medulla chromaffin cell contains a dopaminergic receptor that modulates the catecholamine secretory process triggered by stimulation of the nicotinic cholinoceptor. Such a receptor seems to be of the D2 type and might be involved in a sympatho-adrenal cooperative mechanism contributing to the maintenance of cardiovascular homeostasis during stressful situations as well as to the pathogenesis of hypertension. If so, selective dopaminergic agonists might prove clinically useful in the treatment of hypertension.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1986.tb04513.x
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  • 4
    Electronic Resource
    Electronic Resource
    Separate Binding and Functional Sites for ω co-Conotoxin and Nitrendipine Suggest Two Types of Calcium Channels in Bovine Chromaffin Cells (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 53 (1989), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Purified adrenomedullary plasma membranes contain two high-affinity binding sites for l25I-ω-conotoxin, with KD values of 7.4 and 364 pM and Bmax values of 237 and 1,222 fmol/mg of protein, respectively. Dissociation kinetics showed a biphasic component and a high stability of the toxin-receptor complex, with a t1/2 of 81.6 h for the slow dissociation component. Unlabeled ω-conotoxin inhibited the binding of the radioiodinated toxin, adjusting to a two-site model with Ki1 of 6.8 and Ki2 of 653 pM. Specific binding was not affected by Ca2+ channel blockers or activators, cho-linoceptor antagonists, adrenoceptor blockers, Na+ channel activators, dopaminoceptor blockers, or Na+/H+ antiport blockers, but divalent cations (Ca2+, Sr2+, and Ba2+) inhibited the toxin binding in a concentration-dependent manner. The binding of the dihydropyridine [3H]nitrendipine defined a single specific binding site with a KD of 490 pM and a Bmaxof 129 fmol/mg of protein. At 0.25 μM, co-conotoxin was notable to block depolarization-evoked Ca2+ uptake into cultured bovine adrenal chromaffin cells depolarized with 59 mMK+for 30 s, whereas under the same conditions, 1 μM nitrendipine inhibited uptake by ∼60%. When cells were hyper-polarized with 1.2 mM K+ for 5 min and then Ca2+ uptake was subsequently measured during additions of 59 mMK+, ω-conotoxin partially inhibited Ca2+ uptake in a concentration-dependent manner. These results suggest that two different types of Ca2+ channels might be present in chromaffin cells. However, the molecular identity of ω-conotoxin binding sites remains to be determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1989.tb07394.x
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  • 5
    Electronic Resource
    Electronic Resource
    Characterization of Two Chromaffin Cell Populations Isolated from Bovine Adrenal Medulla (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 57 (1991), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Cultures of chromaffin cells isolated from the bovine adrenal medulla have been extremely useful for investigating secretory mechanisms, but such cultures used up to the present time represent mixed populations of adrenergic and nor-adrenergic cells. This report describes how, with slight modifications to standard procedures, two separate chromaffin cell populations may be separated from bovine adrenal medullae. These two cell fractions have been characterized by biochemical, immunocytochemical, and morphological techniques as enriched populations of adrenergic or noradrenergic cells, respectively. The adrenergic cell-enriched fraction consists of 〉90% adrenergic cells, whereas the noradrenergic cell-enriched fraction contains 〉60% noradrenergic cells. We also demonstrate that these cells may be cultured with their secretory machinery intact: analysis of secreted catecholamines from nicotine- or high K+ concentration-stimulated cells cultured from each fraction confirms that adrenaline is the major catecholamine secreted by one fraction, whereas noradrenaline is mainly secreted by the other.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1991.tb03761.x
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  • 6
    Electronic Resource
    Electronic Resource
    Dihydropyridine Modulation of the Chromaffin Cell Secretory Response (1987)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 48 (1987), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Prolonged perfusion of cat adrenal glands with Krebs-bicarbonate solutions containing nicotine, musca-rine, or excess K rapidly increased the rate of catecholamine output proportional to the concentrations of secretagogue used. The secretory responses to nicotine or high K reached a peak and declined to almost basal rates of secretion after about 10 min of stimulation. The dihydropyridine Ca channel agonist Bay K 8644 potentiated markedly the secretory responses to 1 μM nicotine and to 17.7 mM K but not to higher concentrations of these secretagogues. The musca-rinic response did not decrease with time and was modestly potentiated by Bay K 8644. Similar curves were obtained with 17.7 mM K plus Bay K 8644 and with 59 mMK alone. CGP28392, another agonist, was about 10 times less potent than Bay K 8644 in potentiating the secretory responses to 17.7 mM K. Bay K 8644 also potentiated the release of I3H]noradrenaline evoked by stimulation of cultured bovine adrenal chromaffin cells with 17.7 mMK or 2μM nicotine but not with higher concentrations of K or nicotine. Dihydropyridine Ca channel antagonists reversed the effects of Bay K 8644 with the following order of potency: niludi-pine ≥ nifedipine = nimodipine ≥ nitrendipine. The secretory rates from intact chromaffin cells treated with the Ca ionophores X537A or A23187, or those evoked by Ca-EGTA buffers from digitonin-permeabilized cells, were not affected by Bay K 8644. These results are compatible with the following conclusions: (1) Bay K 8644 selectively potentiates catecholamine secretory responses mediated through the activation of voltage-sensitive Ca channels; (2) during nicotine or high-K stimulation, Ca gains access to the cell interior through a common permeability pathway, the Ca channel; and (3) dihydropyridine Ca agonists and antagonists act on a common site on the chromaffin cell plasma membrane, perhaps a dihydropyridine receptor near the voltage-dependent Ca channel and regulating it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1987.tb04118.x
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  • 7
    Electronic Resource
    Electronic Resource
    Threading dislocations in silicon layer produced by separation by implanted oxygen process (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 2113-2120 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Threading dislocations in the silicon layer in three different types of the silicon on insulator samples produced by standard and improved separation by implanted oxygen (SIMOX) processes were investigated by synchrotron x-ray topography, scanning electron microscopy (SEM), and optical microscopy. The densities and Burgers vectors of the dislocations were first determined nondestructively by synchrotron x-ray topography. Then the line directions of the same dislocations were determined by SEM after chemical Secco etching. Some of these results were compared with results obtained from optical microscopy of Secco etched samples. The threading dislocations in the Si layer were found to occur mainly in pairs with densities of the order of 105 cm−2 in standard SIMOX samples and of the order of 104 cm−2 in improved SIMOX samples. These dislocations have an edge character. Other features of these dislocations, such as the distances between two dislocations forming a pair, orientations of these pairs, and dislocations that change their line direction, are also discussed. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363104
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  • 8
    Electronic Resource
    Electronic Resource
    Magnetization processes in samples with modulated anisotropy under the action of nonuniform magnetic fields (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 3961-3964 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we study the magnetic behavior of amorphous ferromagnetic ribbons having helical anisotropy with the helix axis perpendicular to the sample surface. It is shown that the magnetization processes under the action of a longitudinal magnetic field can be controlled by the nonuniform field produced by an alternating current, of the same frequency than the exciting field, flowing through the sample. Hysteresis loops with very different susceptibilities and coercive fields have been obtained by varying the amplitude of the current intensity and the phase differences between the exciting magnetic field and the current through the sample. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.359917
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  • 9
    Electronic Resource
    Electronic Resource
    Quantum vortex motion in high-Tc superconductors : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6516-6518 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Magnetic relaxation experiments at low temperatures were performed in different zero-field-cooled (ZFC) and field-cooled (FC) high-Tc superconductors (HTSCs): TlBaCaCuO (2212 and 2223 phases, polycrystalline and thin-film samples), (Hg,Tl)BaCaCuO (1223 phase, polycrystalline material), and (Bi,Pb)SrCaCuO (2212 phase, single crystal). For each system and in the whole temperature range investigated, the relaxation curves obtained after both cooling processes are linear with the logarithm of time. The temperature dependence of the relaxation rate normalized to the first magnetization value, R=||d(M/M0)/d ln(t)||, follows a trend which is common to all systems: R decreases linearly with decreasing temperature down to a value, which is called the crossover temperature, below which it levels off to a T-independent plateau. This behavior gives evidence of a transition in the mechanism responsible for the relaxation process at low temperatures, from thermally activated (linear dependence on T) to quantum vortex motion (T-independent regime). The experimental values for the crossover temperatures and normalized relaxation rates compare fairly well to numerical estimates in the framework of the theories of quantum vortex motion in layered HTSCs. Finally, the transition from one regime into another was studied in two samples of the TlBaCaCuO, 2223 phase, system in order to investigate the influence of dissipation on the quantum process. A clear conclusion on this point could not be drawn from these kinds of measurements. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361930
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  • 10
    Electronic Resource
    Electronic Resource
    Intra-4f-shell transitions at room temperature of Er3+ ions in Ca1−xErxF2+x thin films grown on Si(100) (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1133-1137 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Intra-4f-shell transitions of Er3+ ions in Ca1−xErxF2+x thin films were studied by means of photoluminescence (PL) and cathodoluminescence (CL) measurements at room temperature. The samples, with x varying from 0.01 to 0.2, were epitaxially grown on Si(100) substrates by sublimation of solid solution powders. Using the 488-nm line of an Ar+-ion laser as the excitation source, it is shown that the films present strong PL lines corresponding to the internal transitions between the 4S3/2,4F9/2,4I11/2, and 4I13/2 excited levels and the 4I15/2 fundamental state of Er3+ (4f11) ions. Their centers of gravity were pointed out at λ=533, 650, 980, and 1530 nm, respectively. These electronic transitions were also evidenced by means of the CL technique. Moreover, this technique showed that the luminescence is uniform in all points of the layers. The PL intensities vary considerably as a function of the erbium substitution rate. In the visible range the strongest luminescence was found for x less than 0.01, while for the 1530-nm line (which presents evident potential applications for optical communications) the highest luminescence intensity corresponds to x close to 0.16. The refractive index (n) of the layers also varies with the erbium concentration. For a 1.3-μm incident radiation, n continuously increases from 1.425 to 1.466 when x varies from 0.035 to 0.19. This result shows that these structures can lead to the realization of plane optical waveguides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356497
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