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  • 1985-1989  (4)
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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 53 (1989), S. 0 
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Two cell cultures, NEP2 and NEM2, isolated from human foetal brain have been maintained through several passages and found to express some properties of astrocytes. Both cell cultures contain adenylate cyclase stimulated by catecholamines with a potency order of isoprenaline 〉 adrenaline 〉 salbutamol 〈 noradrenaline, which is consistent with the presence of β2-adrenergic receptors. This study reports that the β2-adrenergic-selective antagonist ICI 118,551 is ˜ 1,000 times more potent at inhibiting isoprenaline stimulation of cyclic AMP (cAMP) formation in both NEP2 and NEM2 than the β1adrenergic-selective antagonist practolol. This observation confirms the presence of β2-adrenergic receptors in these cell cultures. The formation of cAMP in NEP2 is also stimulated by 5′-(N-ethylcarboxamido)adenosine (NECA) more potently than by either adenosine or N6-(L-phenylisopropyl)adenosine (L-PIA), which suggests that this foetal astrocyte expresses adenosine A2 receptors. Further more, L-PIA and NECA inhibit isoprenaline stimulation of cAMP formation, a result suggesting the presence of adenosine A1 receptors on NEP2. The presence of A1 receptors is confirmed by the observation that the A1-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine reverses the inhibition of isoprenaline stimulation of cAMP formation by L-PIA and NECA. Additional evidence that NEP2 expresses adenosine receptors linked to the adenylate cyclase-inhibitory GTP-binding protein is provided by the finding that pretreatment of these cells with pertussis toxin reverses the adenosine inhibition of cAMP formation stimulated by either isoprenaline or forskolin.
    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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