Enhancement of airway ciliary beating mediated via voltage-gated Ca channels/α7-nicotinic receptors in mice.

Acetylcholine (ACh), which activates muscarinic ACh receptors (mAChRs) and nicotinic ACh receptors (nAChRs), enhances airway ciliary beating by increasing the intracellular Ca concentration ([Ca]). The mechanisms enhancing airway ciliary beating by nAChRs have remained largely unknown, although those by mAChRs are well understood. In this study, we focused on the effects of α7-nAChRs and voltage-gated Ca channels (Cas) on the airway ciliary beating. The activities of ciliary beating were assessed by frequency (CBF, ciliary beat frequency) and amplitude (CBD, ciliary bend distance) measured by high-speed video microscopy. ACh enhanced CBF and CBD by 25% mediated by an [Ca] increase stimulated by mAChRs and α7-nAChRs (a subunit of nAChR) in airway ciliary cells of mice. Experiments using PNU282987 (an agonist of α7-nAChR) and MLA (an inhibitor of α7-nAChR) revealed that CBF and CBD enhanced by α7-nAChR are approximately 50% of those enhanced by ACh. CBF, CBD, and [Ca] enhanced by α7-nAChRs were inhibited by nifedipine, suggesting activation of Cas by α7-nAChRs. Experiments using a high K solution with/without nifedipine (155.5 mM K) showed that the activation of Cas enhances CBF and CBD via an [Ca] increase. Immunofluorescence and immunoblotting studies demonstrated that Cav1.2 and α7-nAChR are expressed in airway cilia. Moreover, IL-13 stimulated MLA-sensitive increases in CBF and CBD in airway ciliary cells, suggesting an autocrine regulation of ciliary beating by Ca1.2/α7-nAChR/ACh. In conclusion, a novel Ca signalling pathway in airway cilia, Ca1.2/α7-nAChR, enhances CBF and CBD and activates mucociliary clearance maintaining healthy airways.