CAROTID-BODY I-1-IMIDAZOLINE RECEPTORS - BINDING, VISUALIZATION AND MODULATORY FUNCTION

The carotid body is influenced by many neurotransmitter receptors. A n ovel receptor specific for imidazolines has been implicated in cardior espiratory regulation in the brain. To test for both I-1-imidazoline a nd alpha(2)-adrenergic receptors, which also recognize imidazolines, s pecific [I-125]p-iodoclonidine binding to carotid body membranes was c haracterized. The specific alpha(2)-agents epinephrine (100 mu M) or S K&F 86466 (10 mu M) inhibited only a portion of specific [I-125]p-iodo clonidine binding in both cat and rabbit carotid bodies, indicating th e presence of I-1-imidazoline as well as alpha(2)-adrenergic sites. Th e distribution of [I-125]p-iodoclonidine binding sites was visualized autoradiographically. The cat carotid body was intensely labeled by [I -125]p-iodoclonidine, with both I-1-imidazoline and alpha(2)-adrenergi c sites expressed. The relevance of I-1-imidazoline receptors in modul ation of chemosensory discharge was determined in seven cats after alp ha(2)-adrenergic blockade. Clonidine (100 mu g/kg) facilitated chemose nsory activity particularly under hypoxia. We conclude that I-1-imidaz oline receptors are expressed within the carotid body and may potentia te chemosensory discharge, in contrast to the inhibitory action of alp ha(2)-adrenergic receptors. (C) 1998 Elsevier Science B.V. All rights reserved.