[125I]EXP985: A highly potent and specific nonpeptide radioligand antagonist for the AT1 angiotensin receptor

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Abstract

[125I]EXP985 is the first nonpeptide radioligand with high specific activity for the AT1 angiotensin receptor. The biochemical and pharmacological profiles of this ligand were determined using either ligand-receptor binding techniques in rat adrenal cortical microsomes or cellular Ca2+ mobilization in rat smooth muscle cells. Specific binding with 0.1 nM [125I]EXP985 increased slowly with time reaching an equilibrium at 60 min of incubation (22°C). Scatchard analysis of the inhibition / binding data revealed a single class of binding sites having a Kd of 1.49 ± 0.06 nM and a Bmax of 3.6 ± 0.1 pmol/mg protein. These sites were saturable and the ligand-receptor complex dissociated with a t1/2 of 58 min. The binding was inhibited by Ang peptides with the following order of potency and IC50 (nM) : Ang II (3.7) > Ang III (69) > Ang I (3650), and by the nonpeptide AT1 receptor antagonist, losartan, with an IC50 of 3.2 nM, PD123177, an AT2 selective antagonist, showed minimal inhibitory effect. Specific binding of [125I]EXP985 was found on rat aortic smooth cells. Ang II-induced Ca2+ mobilization in these cells was blocked by EXP985 in a noncompetitive manner. These data show that [125I]EXP985 (or its unlabeled) is a potent and highly specific radioligand or noncompetitive antagonist which represents a novel tool to further our understanding of the biochemistry of AT1 receptors.

References (26)

  • A.T. Chiu et al.

    Biochem. Biophys. Res. Commun

    (1989)
  • S. Whitebread et al.

    Biochem. Biophys. Res. Commun

    (1989)
  • A.T. Chiu et al.

    Biochem. Biophys. Res. Commun

    (1990)
  • S. Whitebread et al.

    Biochem. Biophys. Res. Commun

    (1991)
  • A.T. Chiu et al.

    Eur. J. Pharmacol

    (1988)
  • A.T. Chiu et al.

    Biochem. Biophys. Res. Commun

    (1991)
  • P.B.M.W.M. Timmermans et al.

    Trends Pharmacol. Sci

    (1991)
  • N. Iwai et al.

    FEBS Left

    (1992)
  • M.J. Peach et al.

    Adv. Exp. Med

    (1980)
  • M.R. Ujhelyi et al.

    Pharmacotherapy

    (1989)
  • F.M. Bumpus et al.

    Hypertension

    (1991)
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      However, 3H-losartan has considerable non-AT1 receptor binding sites [10]. An attempt was made to radioiodinate the losartan analog, Exp985 [11], but this radioligand abundantly bound to albumin, obscuring AT1 receptor binding. Another nonpeptide AT1 receptor antagonist SK&F 108566 (eprosartan) has been radiolabeled with 3H and used to identify AT1 receptors [12].

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