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  • 1
    Electronic Resource
    Electronic Resource
    Regulation of Guanosine Triphosphate Cyclohydrolase and Tetrahydrobiopterin Levels and the Role of the Cofactor in Tyrosine Hydroxylation in Primary Cultures of Adrenomedullary Chromaffin Cells (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 46 (1986), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Selective modification of the tetrahydrobiopterin levels in cultured chromaffin cells were followed by changes in the rate of tyrosine hydroxylation. Addition of sepiapterin, an intermediate on the salvage pathway for tetrahydrobiopterin synthesis, rapidly increased intracellular levels of tetrahydrobiopterin and elevated the rate of tyrosine hydroxylation in the intact cell. Tyrosine hydroxylation was also enhanced when tetrahydrobiopterin was directly added to the incubation medium of intact cells. When the cultured chromaffin cells were treated for 72 h with N-acetylserotonin, an inhibitor of sepiapterin reductase, tetrahydrobiopterin content and the rate of tyrosine hydroxylation were decreased. Addition of sepiapterin or N-acetylserotonin had no consistent effect on total extractable tyrosine hydroxylase activity or on catecholamine content in the cultured chromaffin cells. Three-day treatment of chromaffin cell cultures with compounds that increase levels of cyclic AMP (forskolin, cholera toxin, theophylline, dibutyryl- and 8-bromo cyclic AMP) increased total extractable tyrosine hydroxylase activity and GTP-cyclohydrolase, the rate-limiting enzyme in the biosynthesis of tetrahydrobiopterin. Tetrahydrobiopterin levels and intact cell tyrosine hydroxylation were markedly increased after 8-bromo cyclic AMP. The increase in GTP-cyclohydrolase and tetrahydrobiopterin induced by 8-bromo cyclic AMP was blocked by the protein synthesis inhibitor cycloheximide. Agents that deplete cellular catecholamines (reserpine, tetrabenazine, and brocresine) increased both total tyrosine hydroxylase and GTP-cyclohydrolase activities, although treating the cultures with reserpine or tetrabenazine resulted in no change in cellular levels of cyclic AMP. Brocresine and tetrabenazine increased tetrahydrobiopterin levels, but the addition of reserpine to the cultures decreased catecholamine and tetrahydrobiopterin content and resulted in a decreased rate of intact cell tyrosine hydroxylation in spite of the increased activity of the total extractable enzyme. These data indicate that in cultured chromaffin cells GTP-cyclohydrolase activity like tyrosine hydroxylase activity is regulated by both cyclic AMP-dependent and cyclic AMP-independent mechanisms and that the intracellular level of tetrahydrobiopterin is one of the many factors that control the rate of tyrosine hydroxylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1986.tb00637.x
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  • 2
    Electronic Resource
    Electronic Resource
    THE ACETYLCHOLINE RECEPTOR OF THE ADRENAL MEDULLA (1977)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 28 (1977), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract— The acetylcholine receptor of the bovine adrenal medulla was studied by specific binding of [1251]α-bungarotoxin to membrane fractions and by perfusion of the isolated gland. The subcellular distribution of the acetylcholine receptor paralleled the distribution of the plasma membrane markers, acetylcholinesterase and calciumstimulated ATPase. The dissociation constant for the binding of α-bungarotoxin to a purified plasma membrane fraction was calculated from Scatchard plots to be 1.6 nM, with a concentration of 190 fmol of binding sites/mg of membrane protein. Correcting for recovery, this corresponds to 0.9 pmol acetylcholine receptor/g adrenal medulla. In decreasing order of effectiveness, d-tubocurarine, nicotine, acetylcholine, carbamylcholine, acetate plus choline, decamethonium, atropine and hexamethonium inhibited binding of α-bungarotoxin.Perfusion experiments showed the acetylcholine receptor to be entirely nicotinic. Stimulation by nicotine was inhibited by atropine and decamethonium, as well as by hexamethonium. Calculated dissociation constants for these antagonist-receptor interactions were in the range of 1 to 3 × 10−5 m. α-Bungarotoxin failed to inhibit nicotine-stimulated catecholamine release in the perfused adrenal, most likely because of its limited diffusion into the gland.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1977.tb10615.x
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  • 3
    Electronic Resource
    Electronic Resource
    ISOLATION AND CHARACTERIZATION OF PLASMA MEMBRANES FROM THE ADRENAL MEDULLA (1976)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 27 (1976), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract– The isolation of a plasma membrane fraction from the bovine adrenal medulla and its characterization are described. The plasma membranes are enriched 13-fold in AChE, a plasma membrane marker, and represent 0.7% of the homogenate membrane protein. The yield of these membranes is typically 10-12% by the criterion of the percentage of total membrane bound AChE in the homogenate. The membranes were characterized as to their polypeptide, phospholipid and cholesterol content and compared with chromaffin vesicle, mitochondrial and microsomal membranes by these parameters.Two enzymatic components of the plasma membranes, ATPase and adenylate cyclase, were also studied. Calcium ATPase activity is 2.5-fold higher than magnesium ATPase activity, appears to be the result of a single enzyme, and is a genuine component of the plasma membranes. The magnesium stimulated activity appears to have at least two enzymatic components, one of which may be identical to the calcium ATPase.Adenylate cyclase is a plasma membrane component, but may not be uniquely localized there, as it is rather unstable throughout the fractionation procedure. It is stimulated by GTP (0.7-fold at 10−5M), GPP(NH)P (4.8-fold at 10−5M) and sodium fluoride (4.6-fold at 10−2M). It is refractory to stimulation by all other compounds tested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1976.tb02606.x
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  • 4
    Electronic Resource
    Electronic Resource
    Toxicity of Chlorine and Other Chlorinated Compounds to Some Australian Aquatic Organisms (1996)
    Springer
    Bulletin of environmental contamination and toxicology 56 (1996), S. 971 -976 
    Details
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s001289900140
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  • 5
    Electronic Resource
    Electronic Resource
    MODELLING OF P-I-N PHOTODIODES UNDER HIGH ILLUMINATION CONDITIONS (1997)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 10 (1997), S. 139-151 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Numerical Methods and Modeling
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The response of a p-i-n photodetector made from gallium arsenide to both steady-state and transient illumination has been modelled. Both an ensemble Monte-Carlo model and a drift-diffusion model were used, the latter with the choice of two different mobility models. The effects of high intensity steady-state illumination on the field and carrier distributions in the photodetector were calculated, and a comparative study of the models made. The transient response to pulsed illumination has also been calculated and the different results obtained from the models explained. The effect of high illumination on the response speed of the detector has been demonstrated. In addition, an expression for obtaining the photocurrent from the Monte-Carlo simulation, with much reduced statistical noise over the conventional estimate, has been derived and successfully tested. © 1997 John Wiley & Sons, Ltd.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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