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  • 1
    Electronic Resource
    Electronic Resource
    Separation of solubilized A2 adenosine receptors of human platelets from non-receptor [3H]NECA binding sites by gel filtration (1988)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 337 (1988), S. 64-68 
    Details
    ISSN: 1432-1912
    Keywords: A2 Adenosine receptor ; Human platelets ; Radioligand binding ; Adenylate cyclase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Human platelet membranes were solubilized with the zwitterionic detergent CHAPS (3-[3-(cholamidopropyl)dimethylammonio]-1-propanesulfonate) and the solubilized extract subjected to gel filtration. Binding of the adenosine receptor agonist [3H]NECA (5′-N-ethylcarboxamidoadeno-sine) was measured to the eluted fractions. Two [3H]NECA binding peaks were eluted, the first of them with the void volume. This first peak represented between 10% and 25% of the [3H]NECA binding activity eluted from the column. It bound [3H]NECA in a reversible, saturable and GTP-dependent manner with an affinity of 46 nmol/1 and a binding capacity of 510 fmol/mg protein. Various adenosine receptor ligands competed for the binding of [3H]NECA to the first peak with a pharmacological profile characteristic for the A2 adenosine receptor as determined from adenylate cyclase experiments. In contrast, most adenosine receptor ligands did not compete for [3H]NECA binding to the second, major peak. These results suggest that a solubilized A2 receptor-GS protein complex of human platelets can be separated from other [3H]NECA binding sites by gel filtration. This allows reliable radioligand binding studies of the A2 adenosine receptor of human platelets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00169478
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    2-Chloro-N6-cyclopentyladenosine: a highly selective agonist at A1 adenosine receptors (1988)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 337 (1988), S. 687-689 
    Details
    ISSN: 1432-1912
    Keywords: Adenosine receptors ; Adenylate cyclase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary 2-Chloro-N6-cyclopentyladenosine (CCPA) was synthesized as a potential high affinity ligand for A1 adenosine receptors. Binding of [3H]PIA to A1 receptors of rat brain membranes was inhibited by CCPA with a K i-value of 0.4 nM, compared to a K i-value of 0.8 nM for the parent compound N6-cyclopentyladenosine (CPA). Binding of [3H]NECA to A2 receptors of rat striatal membranes was inhibited with a K i-value of 3900 nM, demonstrating an almost 10,000-fold A1-selectivity of CCPA. CCPA inhibited the activity of rat fat cell membrane adenylate cyclase, a model for the A1 receptor, with an IC50-value of 33 nM, and it stimulated the adenylate cyclase activity of human platelet membranes with an EC50-value of 3500 nM. The more than 100-fold A1-selectivity compares favourably with a 38-fold selectivity of CPA. Thus, CCPA is an agonist at A1 adenosine receptors with a 4-fold higher selectivity and 2-fold higher affinity than CPA, and a considerably higher selectivity than the standard A1 receptor agonist R-N6-phenylisopropyladenosine (R-PIA). CCPA represents the agonist with the highest selectivity for A1 receptors reported so far.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00175797
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    8-Cyclopentyl-1,3-dipropylxanthine (DPCPX) — a selective high affinity antagonist radioligand for A1 adenosine receptors (1987)
    Springer
    Naunyn-Schmiedeberg's archives of pharmacology 336 (1987), S. 204-210 
    Details
    ISSN: 1432-1912
    Keywords: Adenosine receptors ; Adenylate cyclase ; Phosphodiesterase ; Xanthines ; Radioligands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The properties of 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) as an antagonist ligand for A1 adenosine receptors were examined and compared with other radioligands for this receptor. DPCPX competitively antagonized both the inhibition of adenylate cyclase activity via A1 adenosine receptors and the stimulation via A2 adenosine receptors. The K 1-values of this antagonism were 0.45 nM at the A1 receptor of rat fat cells, and 330 nM at the A2 receptor of human platelets, giving a more than 700-fold A1-selectivity. A similar Al-selectivity was determined in radioligand binding studies. Even at high concentrations, DPCPX did not significantly inhibit the soluble cAMP-phosphodiesterase activity of human platelets. [3H]DPCPX (105 Ci/mmol) bound in a saturable manner with high affinity to A1 receptors in membranes of bovine brain and heart, and rat brain and fat cells (K D-values 50–190 pM). Its nonspecific binding was about 1 % of total at KD, except in bovine myocardial membranes (about 10%). Binding studies with bovine myocardial membranes allowed the analysis of both the high and low agonist affinity states of this receptor in a tissue with low receptor density. The binding properties of [3H]DPCPX appear superior to those of other agonist and antagonist radioligands for the A1 receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00165806
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    Paper (German National Licenses)
    Fulltext
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