Naunyn-Schmiedeberg's Archives of Pharmacology

, Volume 332, Issue 2, pp 179–183

Evaluation of the binding of the A-1 selective adenosine radioligand, cyclopentyladenosine (CPA), to rat brain tissue

  • Michael Williams
  • Albert Braunwalder
  • Thomas J. Erickson
Rudolf Buchheim Lecture

DOI: 10.1007/BF00511410

Cite this article as:
Williams, M., Braunwalder, A. & Erickson, T.J. Naunyn-Schmiedeberg's Arch. Pharmacol. (1986) 332: 179. doi:10.1007/BF00511410

Summary

The binding of [3H]-Cyclopentyladenosine (CPA), an N6-substituted analog of adenosine, was examined in vitro. CPA bound with high affinity (Kd=0.48 nmol/l) to rat brain membranes. Specific binding, which represented 90–97% of the total counts bound at a ligand concentration of 1 nmol/l, was saturable, reversible and sensitive to protein denaturation. The pharmacology of binding was consistent with the labeling of an A-1 receptor, the R- and S-diastereomers of N6-phenylisopropyladenosine (PIA) showing a sixteenfold difference in their ability to displace CPA. The prototypic A-1 selective adenosine agonist, N6-cyclohexyladenosine (CHA) was twofold less active than CPA in displacing radiolabeled CPA. Comparison of the ability of cold CHA and CPA to displace [3H]-CPA gave rat dissociation constants of 1.88 and 1.80×104 s−1, respectively suggesting that both CHA and CPA bound to the same recognition site. In contrast however, comparison of the binding of [3H]-CPA with that of [3H]-CHA showed distinct differences. The Kd for CHA was approximately twice that of CPA while the apparent Bmax was 60% greater. In comparing the pharmacology of CPA binding with that of CHA, it was found that CHA, S-PIA and the antagonist, PACPX were more active in displacing CHA than CPA. In general however, CPA has a binding profile very similar to that observed with CHA.

Key words

Adenosine receptorsCyclopentyladenosineRadioligand binding

Abbreviations

2-CADO

2 chloroadenosine

CHA

N6cyclohexyladenosine

CPA

N6cyclopentyladenosine

EHNA

Erythro-9-(2-hydroxy-3-nonyl)adenine

IBMX

Isobutylmethylxanthine

NECA

5′ N-ethylcarboxamide adenosine

PACPX

[1,3-dipropyl-8-(2-amino-4-chloro)phenylxanthine]

PIA

N6-Phenylisopropyladenosine

Copyright information

© Springer-Verlag 1986

Authors and Affiliations

  • Michael Williams
    • 1
  • Albert Braunwalder
    • 1
  • Thomas J. Erickson
    • 2
  1. 1.Neuroscience/Cardiovascular Research, Pharmaceuticals DivisionCIBA-GEIGY CorporationSummitUSA
  2. 2.Dupont-NEN ProductsBostonUSA