The Japanese herbal medicine, Ryukakusan, enhances mucociliary clearance via TRPV4-mediated tissue-scale ciliary metachronal waves in ciliated Human bronchial/tracheal epithelia

Mucociliary clearance (MCC), which extrudes inhaled small particles from airways, is driven by the beating cilia. Two cellular activities, the ciliary-beat-frequency (CBF) and -distance (CBD, an index of amplitude), facilitate MCC; in addition, an epithelial activity, metachronal waves (MCWs), is suggested to facilitate it. In this study, beating cilia were observed in ciliated normal human bronchial/tracheal epithelial cells (c-NHBE cells) using high-speed video microscopy (HSVM) and the MCWs were detected by kymographs of beating cilia produced from HSVM video images. Ryukakusan (RKS, a Japanese herbal medicine facilitating MCC), which contains platycodon, licorice, apricot kernel and senega, was used for experiments, because it stimulated the MCWs without CBF increase in c-NHBE cells. RKS increased [Ca 2+ ] i by activating TRPV4, leading to increase the MCW-wavelengths (MCW-Ls) and decreased [Cl - ] i by activating Cl - channels, which led to an increase in CBD. Connexin43 activated by TRPV4 transmitted MCWs to adjacent cells, leading to increased MCW-Ls. In RKS-stimulated c-NHBE sheets, increases in the MCW-L and CBD enhanced the microbead transport rate from 245 µm/s to 340 µm/s (p<0.001), while the CBD itself enhanced to 295 µm/s (p<0.001). Thus, the tissue-scale MCWs (long MCW-Ls) enhanced the rates of ciliary microbead transport in c-NHBE sheets, and are an important epithelial function for facilitating MCC in airways. Thus, RKS increasing MCW-Ls and CBD appears to prevent oropharynx epithelia from injury and infections by inhaled particles.