RESUMO
Current concepts on the location and functional significance of nicotinic receptors in the carotid body rest on alpha-bungarotoxin binding and autoradiographic studies. Using an in vitro preparation of the cat carotid body whose catecholamine deposits have been labeled by prior incubation with the tritiated natural precursor [3H]tyrosine, we have found that nicotine induces release of [3H]catecholamines in a dose-dependent manner (IC50 = 9.81 microM). We also found that mecamylamine (50 microM) completely abolished the nicotine-induced release, while alpha-bungarotoxin (100 nM; approximately 20 times its binding Kd) only reduced the release by 56%. These findings indicate that chemoreceptor cells, and perhaps other carotid body structures, contain nicotinic receptors that are not sensitive to alpha-bungarotoxin and force a revision of the current concepts on cholinergic mechanisms in the carotid body chemoreception.
