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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 55 (1990), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Preincubation of D384 cells, derived from the human astrocytoma cell line G-CCM, with dopamine resulted in a time-dependent attenuation of cyclic AMP responsiveness to subsequent dopamine stimulation. This effect was agonist specific because the prostaglandin E1 (PGE,) stimulation of cyclic AMP of similarly treated cells remained unchanged. The attenuation by dopamine was concentration dependent with a maximum observed at 100 μM. A comparison of dopamine concentration-response curves of control and dopamine-preincubated cells revealed no change in the Ka apparent value, but a marked attenuation of the maximal response. Preincubation of cells with dopamine in the presence of D1 but not D2 selective antagonists partially prevented the observed attenuation. Attenuations in dopamine responsiveness were also obtained when D384 cells were preincubated with D1 but not D2 receptor agonists. The level of attenuation attained related to agonist efficiency in stimulating cyclic AMP: SKF38393 〈 3,4-dihydroxynomifensine 〈 fenoldopam 〈 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene = dopamine. However, increasing the efficiency of 3,4-dihydroxynomifensine stimulation of cyclic AMP, using the synergistic effect of adding a low concentration of forskolin, produced no further change in the attenuation of the subsequent response to dopamine. Thus, the D1 dopamine receptors expressed by D384 cells undergo homologous desensitization. Uncoupling of the D1 dopamine receptor appears to be independent of cyclic AMP formation, analogous to a mechanism proposed for the β-adrenergic receptor.
    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: 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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  • 4
    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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  • 5
    ISSN: 1432-1912
    Keywords: B2-Bradykinin receptor ; Intracellular calcium ; Phorbol ester binding ; Cyclic AMP ; D1-dopamine receptor ; Phosphodiesterase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have examined the activation of a phospholipase C signal transduction pathway by a B2-bradykinin receptor in the human astrocytoma cell line D384 and how this influences D1-dopamine receptor stimulated cyclic AMP accumulation. Addition of bradykinin to D384 cells resulted in a concentration-dependent (10−11 − 10−6 M) increase in the accumulation of [3H]inositol phosphates and a similar concentration-dependent transient increase in specific [3H]β-phorbol-12,13-dibutyrate binding which is indicative of translocation of protein kinase C from the cytosol to the membrane. Changes in intracellular Ca2+ of single cells, measured using the fluorescent indicator dye fura-2, indicated that bradykinin produced a rapid, but transient, increase in intracellular calcium. The Ca2+ response was largely independent of extracellular Ca2+ supporting the idea that receptor activation leads to mobilization of Ca2+ from intracellular stores. However, extracellular Ca2+ was required for a response to a rechallenge with bradykinin. The bradykinin B2-receptor agonist kallidin increased cytosolic Ca 2+ in a similar manner to bradykinin. The Ca2+ response to bradykinin could be partially reduced in the presence of the B2-receptor antagonist [d-Arg10-Hyp,d-Phe7,β-(2-Thienyl)-Ala5,8]-bradykinin, whereas the B1-receptor agonists (Des-Arg9]-bradykinin and [Des-Arg10]-kallidin were ineffective. Bradykinin was also found to attenuate dopamine stimulated cyclic AMP accumulation in D384 cells, at similar concentrations previously observed to stimulate the phospholipase C signal transduction pathway, in the presence of the phosphodiesterase inhibitor, rolipram. In contrast, no attenuation was observed in the presence of the phosphodiesterase inhibitor 1-isobutyl 3-methylxanthine, although the level of dopamine stimulated cyclic AMP observed was lower than in the presence of rolipram. Furthermore, the effect of bradykinin could be mimicked by a calcium ionophore, but not a phorbol ester. These data suggest that D384 cells express a B2 bradykinin receptor coupled to polyphosphoinositide-specific phospholipase C. Activation of this receptor results in elevated levels of cytosolic Ca2+ and to a reduction of D1-dopamine receptor stimulated cyclic AMP accumulation.
    Type of Medium: Electronic Resource
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