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3H-(−)-Bupranolol, a new β-adrenoceptor radioligand: Characterization of its binding to kitten heart β-adrenoceptors

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Summary

A technique is described for the synthesis of 3H-(−)-bupranolol (3H-BU) by tritium exchange. The binding of this new radioligand was characterized at 32.5°C on ventricular membrane particles prepared from the hearts of reserpine-pretreated kittens.

  1. 1.

    The dissociation rate constant was determined from the rate at which a saturating concentration (100 μmol/l) of (−)-isoprenaline displaced bound 3H-BU. A k off of 0.3 min−1 was measured.

  2. 2.

    At a concentration of 0.51 nmol/l, 3H-BU quickly associated with heart β-adrenoceptors, yielding a k on of 1.1×109l/mol·min.

  3. 3.

    Saturation binding experiments demonstrated an equilibrium dissociation constant of 0.6 nmol/l and 90–100 fmol binding sites per mg membrane protein. Neither B max nor the affinity were significantly modified by 10 μmol/l phentolamine; nor did 0.1–100 μmol/l phentolamine compete with 3H-BU for membrane binding sites.

  4. 4.

    Unlabeled bupranolol competed in a stereoselective manner with 3H-BU. The best fit to the data produced equilibrium constants of 0.64 nmol/l and 30 nmol/l for (−)-bupranolol and (+)-bupranolol, respectively.

  5. 5.

    Several well-characterized ligands were employed to inhibit the binding of 3H-BU. The resultant affinity estimates agree quantitatively with the expected values.

  6. 6.

    All of the binding data are consistent with a model for a single class of non-interacting sites.

  7. 7.

    3H-BU antagonized in a simple competitive manner the stimulation of the adenylyl cyclase produced by (−)-isoprenaline. A blocking constant of 0.88 nmol/l was found.

  8. 8.

    The estimates of the equilibrium dissociation constant fell between 0.5 and 0.9 nmol/l, in agreement with previous studies on intact tissue preparations. It is concluded that 3H-BU is a useful tool for the study of myocardial β-adrenoceptors.

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Authors and Affiliations

  1. Lehrstuhl für Klinische Physiologie, Physiologisches Institut der Universität Düsseldorf, Universitätsstrasse 1, D-4000, Düsseldorf 1, Federal Republic of Germany

    Tom H. Morris & Alberto J. Kaumann

  2. Abt. Chemie, Sanol Schwarz GmbH, Mittelstrasse 11-13, D-4019, Monheim, Federal Republic of Germany

    Klaus Sandrock

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  1. Tom H. Morris
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  2. Klaus Sandrock
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  3. Alberto J. Kaumann
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Morris, T.H., Sandrock, K. & Kaumann, A.J. 3H-(−)-Bupranolol, a new β-adrenoceptor radioligand: Characterization of its binding to kitten heart β-adrenoceptors. Naunyn-Schmiedeberg's Arch. Pharmacol. 317, 19–25 (1981). https://doi.org/10.1007/BF00506251

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  • DOI: https://doi.org/10.1007/BF00506251

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