Acute nicotine administration stimulates ciliary activity via α3β4 nAChR in the mouse trachea

Mucociliary clearance, the continuous removal of mucus-trapped particles by cilia-driven directed transport of the airway lining fluid, is the primary innate defense mechanism of the airways. It is potently activated by acetylcholine (ACh) addressing muscarinic receptors with a currently less defined role of nicotinic ACh receptors (nAChR). We here set out to determine their contribution in driving ciliary activity in an explanted mouse trachea preparation utilizing selected agonists and antagonists and nAChR-subunit deficient mice. Nicotine (100 mu M) induced an increase in ciliary beat frequency, accompanied by a sharp, but not long lasting increase in particle transport speed (PTS) on the mucosal surface showing marked desensitization within the next 30 min. Nicotine-induced PTS acceleration was sensitive to the general nAChR inhibitors mecamylamine and d-tubocurarine as well as to the alpha 3 beta 4-nAChR antagonist alpha-conotoxin AulB, but not to other antagonists primarily addressing alpha 3 beta 2-nAChR or alpha 4-, alpha 7- and alpha 9-containing nAChR. Agonists at alpha 3 beta*-nAChR (epibatidine, cytisine), but not cotinine mimicked the effect. Tracheas from mice with genetic deletion of nAChR subunits alpha 5, alpha 7, alpha 9, alpha 10, alpha 9/10, and beta 2 retained full PTS response to nicotine, whereas this was entirely lost in tracheas from mice lacking the beta 4-subunit Collectively, our data show that nicotinic stimulation of alpha 3 beta 4-nAChR acutely increases PTS to the same extent as the established strong activator ATP. In view of the marked desensitization observed in the present setting, the physiological relevance of these receptors in adapting mucociliary clearance to rapidly changing endogenous or environmental stimuli remains open.