EVIDENCE FOR 2 TYPES OF NICOTINIC RECEPTORS IN THE CAT CAROTID-BODY CHEMORECEPTOR CELLS

Current concepts on the location and functional significance of nicoti nic receptors in the carotid body rest on alpha-bungarotoxin binding a nd autoradiographic studies. Using an in vitro preparation of the cat carotid body whose catecholamine deposits have been labeled by prior i ncubation with the tritiated natural precursor [H-3]tyrosine, we have found that nicotine induces release of [H-3]catecholamines in a dose-d ependent manner (IC50=9.81 mu M). We also found that mecamylamine (50 mu M) completely abolished the nicotine-induced release, while alpha-b ungarotoxin (100 nM; approximate to 20 times its binding K-d) only red uced the release by 56%. These findings indicate that chemoreceptor ce lls, and perhaps other carotid body structures, contain nicotinic rece ptors that are not sensitive to alpha-bungaroroxin and force a revisio n of the current concepts on cholinergic mechanisms in the carotid bod y chemoreception.