Naunyn-Schmiedeberg's Archives of Pharmacology

, Volume 340, Issue 6, pp 679–683 | Cite as

2-Chloro-N6-[3H]cyclopentyladenosine ([3HCCPA) —a high affinity agonist radioligand for A1 adenosine receptors

  • Karl-Norbert Klotz
  • Martin J. Lohse
  • Ulrich Schwabe
  • Gloria Cristalli
  • Sauro Vittori
  • Mario Grifantini


The tritiated analogue of 2-chloro-N6-cyclopentyladenosine (CCPA), an adenosine derivative with subnanomolar affinity and a 10000-fold selectivity for A1 adenosine receptors, has been examined as a new agonist radioligand. [3H]CCPA was prepared with a specific radioactivity of 1.58 TBq/mmol (43 Ci/mmol) and bound in a reversible manner to A1 receptors from rat brain membranes with a high affinityKD-value of 0.2 nmol/l. In the presence of GTP aKD-value of 13 nmol/l was determined for the low affinity state for agonist binding. Competition of several adenosine receptor agonists and antagonists for [3H]CCPA binding to rat brain membranes confirmed binding to an A1 receptor. Solubilized A1 receptors bound [3H]CCPA with similar affinity for the high affinity state. At solubilized receptors a reduced association rate was observed in the presence of MgCl2, as has been shown for the agonist [3H]N6-phenylisopropyladenosine ([3H]PIA). [3H]CCPA was also used for detection of A1 receptors in rat cardio myocyte membranes, a tissue with a very low receptor density. A KD-value of 0.4 nmol/l and aBmax-value of 16 fmol/ mg protein was determined in these membranes. In human platelet membranes no specific binding of [3H]CCPA was measured at concentrations up to 400 nmol/l, indicating that A2 receptors did not bind [3H]CCPA. Based on the subnanomolar affinity and the high selectivity for A1 receptors [3H]CCPA proved to be a useful agonist radioligand for characterization of A1 adenosine receptors also in tissues with very low receptor density.

Key words

Adenosine receptors Radioligands Agonists 





















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Copyright information

© Springer-Verlag 1989

Authors and Affiliations

  • Karl-Norbert Klotz
    • 1
  • Martin J. Lohse
    • 1
  • Ulrich Schwabe
    • 1
  • Gloria Cristalli
    • 2
  • Sauro Vittori
    • 2
  • Mario Grifantini
    • 2
  1. 1.Pharmakologisches Institut der Universität HeidelbergHeidelbergGermany
  2. 2.Dipartimento di Scienze ChimicheUniversità di CamerinoCamerinoItaly

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