Ciliary Motility Decreased by a CO 2 /HCO 3 - -Free Solution in Ciliated Human Nasal Epithelial Cells Having a pH Elevated by Carbonic Anhydrase IV.

An application of CO 2 /HCO 3 - -free solution (Zero-CO 2 ) did not increase intracellular pH (pH i ) 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 i of c-hNECs expressing carbonic anhydrase IV (CAIV) is high (7.64), while the pH i of ciliated human bronchial epithelial cells (c-hBECs) expressing no CAIV is low (7.10). An extremely high pH i of c-hNECs caused pH i , CBF and CBA to decrease upon Zero-CO 2 application, while a low pH i of c-hBECs caused them to increase. An extremely high pH i was generated by a high rate of HCO 3 - influx via interactions between CAIV and Na + /HCO 3 - cotransport (NBC) in c-hNECs. An NBC inhibitor (S0859) decreased pH i , CBF and CBA and increased CBF and CBA in c-hNECs upon Zero-CO 2 application. In conclusion, the interactions of CAIV and NBC maximize HCO 3 - influx to increase pH i in c-hNECs. This novel mechanism causes pH i to decrease, leading to no increase in CBF and CBA in c-hNECs upon Zero-CO 2 application, and appears to play a crucial role in maintaining pH i , CBF and CBA in c-hNECs periodically exposed to air (0.04% CO 2 ) with respiration.