Carotid body I1-imidazoline receptors: binding, visualization and modulatory function

Respir Physiol. 1998 Jun;112(3):239-51. doi: 10.1016/s0034-5687(98)00021-8.


The carotid body is influenced by many neurotransmitter receptors. A novel receptor specific for imidazolines has been implicated in cardiorespiratory regulation in the brain. To test for both I1-imidazoline and alpha2-adrenergic receptors, which also recognize imidazolines, specific [125I]p-iodoclonidine binding to carotid body membranes was characterized. The specific alpha2-agents epinephrine (100 microM) or SK&F 86466 (10 microM) inhibited only a portion of specific [125I]p-iodoclonidine binding in both cat and rabbit carotid bodies, indicating the presence of I1-imidazoline as well as alpha2-adrenergic sites. The distribution of [125I]p-iodoclonidine binding sites was visualized autoradiographically. The cat carotid body was intensely labeled by [125I]p-iodoclonidine, with both I1-imidazoline and alpha2-adrenergic sites expressed. The relevance of I1-imidazoline receptors in modulation of chemosensory discharge was determined in seven cats after alpha2-adrenergic blockade. Clonidine (100 microg/kg) facilitated chemosensory activity particularly under hypoxia. We conclude that I1-imidazoline receptors are expressed within the carotid body and may potentiate chemosensory discharge, in contrast to the inhibitory action of alpha2-adrenergic receptors.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adrenergic alpha-Agonists / pharmacokinetics
  • Adrenergic alpha-Agonists / pharmacology
  • Affinity Labels
  • Animals
  • Autoradiography
  • Carotid Body / anatomy & histology
  • Carotid Body / metabolism
  • Carotid Body / physiology*
  • Cats
  • Clonidine / analogs & derivatives
  • Clonidine / pharmacokinetics
  • Guanabenz / pharmacology
  • Hypoxia / metabolism
  • Imidazoline Receptors
  • Iodine Radioisotopes
  • Membranes / drug effects
  • Membranes / metabolism
  • Rabbits
  • Radioligand Assay
  • Receptors, Adrenergic, alpha-2 / drug effects
  • Receptors, Adrenergic, alpha-2 / metabolism
  • Receptors, Drug / metabolism*


  • Adrenergic alpha-Agonists
  • Affinity Labels
  • Imidazoline Receptors
  • Iodine Radioisotopes
  • Receptors, Adrenergic, alpha-2
  • Receptors, Drug
  • 4-iodoclonidine
  • Guanabenz
  • Clonidine