[3H]p-aminoclonidine and [3H]idazoxan label different populations of imidazoline sites on rat kidney

Eur J Pharmacol. 1993 Feb 23;232(1):79-87. doi: 10.1016/0014-2999(93)90731-v.

Abstract

In the presence of RS-15385-197 to preclude binding to alpha 2-adrenoceptors, [3H]p-aminoclonidine labelled a low affinity high capacity site, (Kd = 127.6 +/- 19.7 nM, Bmax 978 +/- 172 fmol/mg protein) whereas [3H]idazoxan labelled a high affinity low capacity site (Kd = 1.66 +/- 0.28 nM, Bmax 45.3 +/- 11.4 fmol/mg protein). Clonidine and p-aminoclonidine showed moderate affinity for the site labelled by [3H]p-aminoclonidine, but low affinity for the site labelled by [3H]idazoxan, whereas idazoxan showed high affinity for [3H]idazoxan and low affinity for [3H]p-aminoclonidine binding. Naphazoline inhibited [3H]idazoxan in a biphasic manner suggesting that [3H]idazoxan may label an heterogeneous population of imidazoline sites. GTP inhibited [3H]idazoxan but not [3H]p-aminoclonidine binding. These results suggest that [3H]idazoxan labelled imidazoline I2 binding sites, whereas [3H]p-aminoclonidine labelled a novel subtype which showed marked differences to the imidazoline I1 binding site reported in bovine and human brainstem.

MeSH terms

  • Adrenergic alpha-Antagonists / pharmacology
  • Animals
  • Binding, Competitive
  • Clonidine / analogs & derivatives*
  • Dioxanes*
  • Guanosine Triphosphate / pharmacology
  • Idazoxan
  • Imidazoles / metabolism*
  • Imidazoline Receptors
  • In Vitro Techniques
  • Isoquinolines / pharmacology
  • Kidney / metabolism*
  • Male
  • Naphazoline / pharmacology
  • Naphthyridines / pharmacology
  • Radioligand Assay
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Drug / metabolism*
  • Tritium

Substances

  • Adrenergic alpha-Antagonists
  • Dioxanes
  • Imidazoles
  • Imidazoline Receptors
  • Isoquinolines
  • Naphthyridines
  • Receptors, Drug
  • Tritium
  • apraclonidine
  • Guanosine Triphosphate
  • Naphazoline
  • Delequamine
  • Clonidine
  • Idazoxan