Analysis of the Pharmacological and Molecular Heterogeneity of I2-Imidazoline-Binding Proteins using Monoamine Oxidase-Deficient Mouse Models

  1. Anne Remaury1,
  2. Rita Raddatz2,
  3. Catherine Ordener1,
  4. Sandra Savic2,
  5. Jean C. Shih3,
  6. Kevin Chen3,
  7. Isabelle Seif4,
  8. Edward De Maeyer4,
  9. Stephen M. Lanier2 and
  10. Angelo Parini1
  1. 1Institut National de la Sante et de la Recherche Medicale, Pharmacologie Moléculaire et Physiopathologie Rénale, Institut Louis Bugnard, Centre Hospitalier Universitaire Rangeuil, Toulouse, France (A.R., C.O., A.P.); 2Department of Pharmacology, Medical University of South Carolina, Charleston, South Carolina (R.R., S.S., S.M.L.); 3Department of Molecular Pharmacology and Toxicology, School of Pharmacy, and Department of Cell and Neurobiology, School of Medicine, University of Southern California, Los Angeles, California (J.C.S., K.C.); and 4Centre National de la Recherche Scientifique, Unite Mixte de Recherche, Institut Curie, Orsay, France (I.S., E.D.M.)

    Abstract

    The I2 subgroup of imidazoline-binding sites was identified as monoamine oxidases (MAOs), but it is unclear whether there are I2-binding sites located on proteins distinct from MAOs. To address this issue, we characterized I2-binding proteins in liver and brain of wild-type and MAO A- and MAO B-deficient mice. I2-binding sites were identified using [3H]idazoxan and the photoaffinity adduct 2-[3-azido-4-[125I]iodophenoxyl]methylimidazoline ([125I]AZIPI). [3H]Idazoxan labeled binding sites with ligand recognition properties typical of I2sites in both brain and liver of wild-type mice. High-affinity, specific [3H]idazoxan binding were not altered in MAO A knockout (KO) mice. In contrast, [3H]idazoxan binding was completely abolished in both liver and brain of MAO B KO mice. In wild-type mice, [125I]AZIPI photolabeled three proteins with apparent molecular masses of ∼28 (liver), ∼61 (brain), and ∼55 kDa (liver and brain). The photolabeling of each protein was blocked by the imidazoline cirazoline (10 μM). Photolabeling of the ∼61- and ∼55-kDa proteins was not observed in MAO A and B KO mice, respectively. In contrast, photolabeling of the liver ∼28-kDa protein was still observed in MAO-deficient mice, indicating that this protein is unrelated to MAOs. These data indicate that I2 imidazoline-binding sites identified by [3H]idazoxan reside solely on MAO B. The binding sites on MAO A and the liver ∼28-kDa protein may represent additional subtypes of the family of the imidazoline-binding sites.

    Footnotes

    • Send reprint requests to: Angelo Parini, M.D., Ph.D., INSERM U388, Institut Louis Bugnard, CHU Rangueil, 31403 Toulouse Cedex 4, France. E-mail: Parini{at}inserm.rangueil.fr

    • This work was supported by Institut National de la Santéet de la Recherche Médicale, the Région Midi-Pyrénées, the Center National de la Recherche Scientifique, the Curie Institute, the National Institute of Mental Health Grant R37 MH39085 (MERIT Award) and NS35875 (S.M.L.), KO5 MH00796 (Research Scientist Award), RO1 MH37020, and the Welin Professorship, T32-HL-7260 (R.R., S.M.L.) and F32 NS10332 (R.R.). A.R. is the recipient of a grant from I.R.I. Servier (France).

    • Abbreviations:
      I2BS
      I2-imidazoline-binding sites
      MAO
      monoamine oxidase
      [125I]AZIPI
      2-[3-azido-4-[125I]iodophenoxyl]methyl imidazoline
      KO
      knockout
      • Received December 29, 1999.
      • Accepted August 2, 2000.
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    1. Molecular Pharmacology November 1, 2000 vol. 58 no. 5 1085-1090
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