Ambroxol-Enhanced Frequency and Amplitude of Beating Cilia Controlled by a Voltage-Gated Ca²⁺ Channel, Cav1.2, via pH_i Increase and [Cl^-]_i Decrease in the Lung Airway Epithelial Cells of Mice

Ambroxol (ABX), a frequently prescribed secretolytic agent which enhances the ciliary beat frequency (CBF) and ciliary bend angle (CBA, an index of amplitude) by 30%, activates a voltage-dependent Ca2+ channel (Ca(V)1.2) and a small transient Ca2+ release in the ciliated lung airway epithelial cells (c-LAECs) of mice. The activation of Ca(V)1.2 alone enhanced the CBF and CBA by 20%, mediated by a pH(i) increase(i) and a [Cl-](i) decrease in the c-LAECs. The increase in pH(i), which was induced by the activation of the Na+-HCO3- cotransporter (NBC), enhanced the CBF (by 30%) and CBA (by 15-20%), and a decrease in [Cl-](i), which was induced by the Cl- release via anoctamine 1 (ANO1), enhanced the CBA (by 10-15%). While a Ca2+-free solution or nifedipine (an inhibitor of Ca(V)1.2) inhibited 70% of the CBF and CBA enhancement using ABX, Ca(V)1.2 enhanced most of the CBF and CBA increases using ABX. The activation of the Ca(V)1.2 existing in the cilia stimulates the NBC to increase pH(i) and ANO1 to decrease the [Cl-](i) in the c-LAECs. In conclusion, the pH(i) increase and the [Cl-](i) decrease enhanced the CBF and CBA in the ABX-stimulated c-LAECs.