Carotid body I1-imidazoline receptors: binding, visualization and modulatory function.
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.
Ernsberger
P
P
Department of Nutrition, Case Western Reserve School of Medicine, Cleveland, OH 44106-4906, USA. pre@po.cwru.edu
Kou
Y R
YR
Prabhakar
N R
NR
D000316:Adrenergic alpha-Agonists / Q000493:pharmacokinetics / Q000494:pharmacology; D000345:Affinity Labels; D000818:Animals; D001345:Autoradiography; D002344:Carotid Body / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology*; D002415:Cats; D003000:Clonidine / Q000031:analogs & derivatives / Q000493:pharmacokinetics; D006143:Guanabenz / Q000494:pharmacology; D000860:Hypoxia / Q000378:metabolism; D054755:Imidazoline Receptors; D007457:Iodine Radioisotopes; D008566:Membranes / Q000187:drug effects / Q000378:metabolism; D011817:Rabbits; D011869:Radioligand Assay; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000378:metabolism; D011955:Receptors, Drug / Q000378:metabolism*
D000316:Adrenergic alpha-Agonists; D000345:Affinity Labels; D054755:Imidazoline Receptors; D007457:Iodine Radioisotopes; D018341:Receptors, Adrenergic, alpha-2; D011955:Receptors, Drug; C053113:4-iodoclonidine; D006143:Guanabenz; D003000:Clonidine