Ciliary Motility Decreased by a CO/HCO-Free Solution in Ciliated Human Nasal Epithelial Cells Having a pH Elevated by Carbonic Anhydrase IV.

An application of CO/HCO-free solution (Zero-CO) did not increase intracellular pH (pH) in ciliated human nasal epithelial cells (c-hNECs), leading to no increase in frequency (CBF) or amplitude (CBA) of the ciliary beating. This study demonstrated that the pH of c-hNECs expressing carbonic anhydrase IV (CAIV) is high (7.64), while the pH of ciliated human bronchial epithelial cells (c-hBECs) expressing no CAIV is low (7.10). An extremely high pH of c-hNECs caused pH, CBF and CBA to decrease upon Zero-CO application, while a low pH of c-hBECs caused them to increase. An extremely high pH was generated by a high rate of HCO influx via interactions between CAIV and Na/HCO cotransport (NBC) in c-hNECs. An NBC inhibitor (S0859) decreased pH, CBF and CBA and increased CBF and CBA in c-hNECs upon Zero-CO application. In conclusion, the interactions of CAIV and NBC maximize HCO influx to increase pH in c-hNECs. This novel mechanism causes pH to decrease, leading to no increase in CBF and CBA in c-hNECs upon Zero-CO application, and appears to play a crucial role in maintaining pH, CBF and CBA in c-hNECs periodically exposed to air (0.04% CO) with respiration.