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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 50 (1988), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Benzodiazepine-affinity chromatography, on a column of 1012S-Sepharose, resulted in the detection and purification of a binding protein (P36) from the cytosolic fraction of pig cerebral cortex. Purified P36 was enriched over 3,500-fold in a single step and was recovered with an efficiency of 50–60%. Analysis of the purified preparation by sodium dodecyl sulphate-polyacrylamide gel electrophoresis demonstrated a single polypeptide of Mr 36,000. TheStokes radius (3.44 nm) and sedimentation coefficient (4.43S) indicated that purified P36 is a dimeric protein. Analysis of the amino acid composition of P36 revealed a relatively high content of the hydrophobic amino acids, valine and leucine. Immunoblotting of several pig tissue preparations with an antiserum raised against purified P36 demonstrated approximately equal enrichment of P36 in cerebral cortex, cerebellum, and adrenal glands. Lesser enrichment was observed in kidney and liver, whereas a number of other tissues displayed no immunoreactivity. The γ-aminobutyrate/benzodiazepine receptor complex and P36 showed no immunological cross-reactivity. High-affinity binding activity for [3H]Ro 15–4513, [3H]flunitrazepam, or [3H]PK11195 was not detected in preparations of purified P36. However, the ability of the γ-aminobutyrate/benzodiazepine receptor inverse agonists, methyl- and ethyl-#bT-carboline-3-carboxylate, to inhibit the binding of P36 to 1012S-Sepharose at relatively low concentrations indicates that P36 exhibits a degree of binding specificity.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Clones have been isolated from the human astrocytoma cell line G-CCM. Homogenates of clone D384 contain an adenylate cyclase that is stimulated by 3,4-dihydroxyphenylethylamine (dopamine), noradrenaline, and isoprenaline with Ka apparent values of 4, 56, and 2.7 μM, respectively. The Ka apparent value for dopamine was increased by the D-l antagonist cis-flupenthixol, 25 and 100 nM, to 23 and 190 μM, respectively, but was unaffected by propranolol (1 μf. Noradrenaline stimulation of adenylate cyclase was only partially inhibited by either propranolol (10 μM) or cis-flupenthixol (1 μM). Propranolol (10 μM), but not cis-flupenthixol (1 μM), prevented stimulation by isoprenaline. The stimulation of adenylate cyclase by dopamine and noradrenaline remained unchanged in the presence of phentolamine (1 μM) and sulpiride (1 μM). These results suggest that clone D384 contains both D-l dopaminergic and β-adrenergic receptors coupled to adenylate cyclase. Dopamine stimulates D384 adenylate cyclase through D-1 receptors, isoprenaline via β-receptors, and noradrenaline through both receptors.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The effects of steroid hormones on the cyclic AMP responses to stimulation of human astrocytoma cells (D384) by dopamine, prostaglandin E1 (PGE1), and isoprenaline were investigated. Incubation of D384 cells with dexamethasone resulted in a potentiation of the PGE1 and isoprenaline responses and a marked attenuation of the dopamine response. The time courses of the effects of dexamethasone on dopamine and PGE1 responses were similar, requiring long-term (at least 18 h) incubation of cells with the steroid. Concentration-response curves of dexamethasone effects on dopamine and PGE1 responses yielded similar Ka apparent values, suggesting a common mechanism. Cycloheximide, a protein synthesis inhibitor, prevented the effects of dexamethasone. Only steroids with glucocorticoid activity reproduced the dexamethasone effects. Direct stimulation of Gs with 5-guanylylimidodiphosphate and adenylate cyclase with forskolin revealed no significant differences in their activities in dexamethasone-treated and untreated cells. Furthermore, a comparison of the dopamine and PGE1 concentration-response curves obtained from dexamethasone-treated and untreated cells suggested that the affinity of the receptors for their agonists remained unchanged. These results suggest that glucocorticoids may alter protein synthesis and thereby the number of receptors expressed by D384 cells.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The electric organ of Torpedo marmorata contains a membrane-bound, captopril-sensitive metallopepti-dase that resembles mammalian angiotensin converting enzyme (peptidyl dipeptidase A; EC 3.4.15.1). The Torpedo enzyme has now been purified to apparent homogeneity from electric organ by a procedure involving affinity chro-matography using the selective inhibitor lisinopril immobilised to Sepharose via a 28-Å spacer arm. The purified protein, like the mammalian enzyme, acted as a peptidyl dipeptidase in cleaving dipeptides from the C-terminus of a variety ofpeptide substrates, including angiotensin I, brady-kinin, [Met5]enkephalin, [Leu5]enkephalin, and the model substrate hippuryl (benzoylglycyl; BzGly)-His-Leu. The hydrolysis of BzGly-His-Leu was activated by Cl−. Enzyme activity was inhibited by classical angiotensin converting enzyme inhibitors, including captopril, enalaprilat (MK422), and lisinopril (MK521). Torpedo angiotensin converting enzyme, like its mammalian counterpart, was also able to act as an endopeptidase in hydrolysing the amidated neuro-peptide substance P. Hydrolysis of substance P occurred primarily at the Phe8-Gly9 bond with release of the C-terminal tripeptide, Gly-Leu-MetNH2, and this hydrolysis was blocked by selective inhibitors. The Torpedo enzyme was recognised by a polyclonal antibody to pig kidney angiotensin converting enzyme on immunoelectrophoretic (Western) blot analysis. Thus, on the basis of substrate specificity, inhibitor sensitivity, and immunological criteria, the Torpedo enzyme closely resembles mammalian angiotensin converting enzyme. However, the Torpedo enzyme appears somewhat larger (Mr= 190,000) than the pig kidney enzyme (Mr= 180,000) on sodium dodecyl sulphate-poly-acrylamide gel electrophoresis. The endogenous peptide substrate(s) for Torpedo electric organ angiotensin converting enzyme and the physiological role of the enzyme in this tissue remain to be evaluated.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: 3,4-Dihydroxyphenylethylamine (dopamine) and β-adrenergic receptor agonists and antagonists were assessed for their effects on cyclic AMP accumulation in human astrocytoma derived clone D384 cells. Dopamine, SKP 38393, and 2-amino-6,7-dihydroxy-l,2,3,4-tetrahydronaphthalene increased cyclic AMP content with Ka values of 2.0, 0.2, and 1.6 μM. The D1-selective antagonists SCH 23390 (Ki, 1.2 nM) and SKF 83566 (Ki, 0.8 nM) were over 5,000-fold more potent than the D2-selective antagonist domperidone (Ki, 6.7 μM) at inhibiting dopamine stimulation of cyclic AMP formation. SCH 23388 (Ki, 560 nM; the S-enantiomer of SCH 23390) was 400-fold less potent than SCH 23390. Isopren-aline, adrenaline, salbutamol, and noradrenaline increased cyclic AMP content with Ka values of 0.13, 0.12, 0.22, and 7.60 μM. The β2-selective antagonist ICI 118,551 (Ki, 0.8 nM) was almost 8,000-fold more potent than the β,-selective antagonist practolol (Ki, 5.9 μM) at inhibiting isoprenaline stimulated cyclic AMP accumulation. These results demonstrate that D384 cells express D1-dopamine and β2-adren-ergic receptors linked to adenylate cyclase. Furthermore, the dopamine receptor expressed by D384 cells exhibits a pharmacological profile typical of a mammalian striatal D1-re-ceptor and therefore the use of this clone represents another approach to studying central D1-receptors.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 49 (1987), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract Neuronal cells in primary culture from 1-day-old brains of normotensive, Wistar-Kyoto strain (WKY) and spontaneously hypertensive (SH) rats have been utilized to study the expression of α1-adrenergic receptors. Binding of a selective α1 antagonist, [125I]2-[β-(4-hydroxy-3-iodophenyl)-ethylaminomethyl]-tetralone ([125I]HEAT) to neuronal membranes prepared from primary brain cultures of WKY and SH rats was 75–80% specific, rapid, and time-dependent although the binding was 1.5–2 times higher in neuronal membranes from SH rat brain cultures. Kinetic analysis of the association and dissociation data demonstrated no significant differences between rat strains. Competition-inhibition experiments provided IC50 values for various antagonists and agonists in the following order: prazosin 〈 phentolamine 〈 yohimbine 〈 phenylephrine 〈 norepinephrine 〈 propranolol, suggesting that [125I]-HEAT bound selectively to α1-adrenergic receptors. Scatchard analysis of the binding data provided straight lines for both strains of rats, indicating the presence of a homogeneous population of binding sites. It also showed that the increase in the binding in neuronal cells from SH rat brains over those from normotensive WKY controls was a result of an increase in the number of α1-adrenergic receptors. Incubation of neuronal cultures from both strains of rats with phenylephrine, an α1-adrenergic agonist, caused a time- and dose-dependent decrease in the binding of [125I]HEAT. This decrease was due to a decrease in the number of α1-adrenergic receptors. In conclusion, we demonstrated that the expression of α1-adrenergic receptors in neuronal cultures of SH rat brain was increased compared with neuronal cultures from normotensive controls. We suggest that the elevated number of these receptors in neurons from the brains of SH rats is an intrinsic property of these cells and therefore provides an etiological basis for the predisposition of these animals to the hypertensive state.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of medicinal chemistry 11 (1968), S. 618-620 
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of medicinal chemistry 21 (1978), S. 1235-1242 
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1520-4804
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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