Acetylcholine

Airway mucociliary transport is an important function for the clearance of inhaled foreign particulates in the respiratory tract. The present study aimed at investigating the regulatory mechanism of acetylcholine (Ach)-induced ciliary beat of the human nasal mucosa in ex vivo. The inferior turbinate mucosa was collected from patients with chronic hypertrophic rhinitis during endoscopic surgery. The mucosa was cut into thin strips, and ciliary movement was observed under a phase-contrast light microscope with a high-speed digital video camera. The sample was alternatively subjected to scanning electron microscopic observation. Cilia on the turbinate epithelium were well preserved at the ultrastructural level. The baseline ciliary beat frequency (CBF) was 6.45？±？0.32 Hz. CBF was significantly increased by stimulation with 100 μM Ach and 100 μM adenosine triphosphate. The Ach-induced CBF increase was completely inhibited by removing extracellular Ca2+. Significant inhibition of the Ach-induced CBF was also observed by the addition of 1 μM atropine, 40 μM 2-aminoethoxydiphenyl borate (inositol trisphosphate [IP3] receptor antagonist), 10 μM carbenoxolone (pannexin-1 blocker), 1 mM probenecid (pannexin-1 blocker), 100 μM pyridoxalphosphate-6-azophenyl-20,40-disulfonic acid (P2X antagonist), and 300 μM flufenamic acid (connexin blocker). Meanwhile, 30 nM bafilomycin A1 (vesicular transport inhibitor) did not inhibit the Ach-induced CBF increase. Conclusions: These results indicate that the regulatory mechanism of the Ach-induced ciliary beat is dependent on extracellular Ca2+ and involves the muscarinic Ach receptor, IP3 receptor, pannexin-1 channel, purinergic P2X receptor, and connexin channel. We proposed a tentative intracellular signaling pathway of the Ach-induced ciliary beat, in which the pannexin-1-P2X unit may play a central role in ciliary beat regulation