Evidence for two types of nicotinic receptors in the cat carotid body chemoreceptor cells

Abstract

Current concepts on the location and functional significance of nicotinic receptors in the carotid body rest on α-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 (IC 50=9.81 μM). We also found that mecamylamine (50 μM) completely abolished the nicotine-induced release, while α-bungarotoxin (100 nM; ≈20 times its binding K d) 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 α-bungarotoxin and force a revision of the current concepts on cholinergic mechanisms in the carotid body chemoreception.