BACKGROUND: Curaremimetic nondepolarizing muscle relaxants are widely used in clinical practice to prevent muscle contraction either during surgery or during intensive care. Although primarily acting at the neuromuscular junction, these compounds can cause adverse effects, including modification of cardiac rhythm, arterial blood pressure, and in the worst cases, triggering of seizures. In this study, we assessed the interaction of atracurium and its metabolite, laudanosine, with neuronal nicotinic receptors. METHODS: The human neuronal nicotinic receptors alpha4beta2, alpha3beta4, alpha3alpha5beta4, and alpha7 are heterologously expressed in Xenopus laevis oocytes, and the effect of atracurium and its degradation product, laudanosine, were studied on these receptors. RESULTS: Atracurium and laudanosine inhibited in the micromolar range the major brain alpha4beta2 receptor and the ganglionic alpha3beta4 or alpha3beta4alpha5 and the homomeric alpha7 receptors. For all four receptors, inhibition was rapid and readily reversible within less than 1 min. Atracurium blockade was competitive at alpha4beta2 and alpha7 receptors but displayed a noncompetitive blockade at the alpha3beta4 receptors. Inhibition at this receptor subtype was not modified by alpha5. Laudanosine was found to have a dual mode of action; first, it competes with acetylcholine and, second, it blocks the ionic pore by steric hindrance. At low concentrations, these two drugs are able to activate both the alpha4beta2 and the alpha3beta4 receptors. CONCLUSION: Adverse effects observed during atracurium administration may be attributed, at least partly, to an interaction with neuronal nicotinic receptors.