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