Ambroxol-enhanced frequency and amplitude of beating cilia mediated by pHi and [Cl-]i in lung airway epithelial cells of mice

Abstract Ambroxol (ABX), a frequently prescribed secretolytic agent that stimulates Ca 2+ release from acidic stores and Ca 2+ entry through Ca V 1.2, enhanced the ciliary beat frequency (CBF) and ciliary bend angle (CBA, an index of amplitude) by 30% in ciliated lung airway epithelial cells (c-LAECs) of mice. An increase in the intracellular Ca 2+ concentration ([Ca 2+ ] i ) stimulated by ABX triggers two signals in c-LAECs; an increase in pH i (pH pathway) and a decrease in [Cl - ] i (Cl - pathway). The pH pathway, which was activated by the HCO 3 - entry through Na + -HCO 3 - cotransporter (NBC) and inhibited by 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS), enhanced the CBF (by 30%) and CBA (by 15-20%) and the Cl - pathway, which was activated by Cl - secretion through anoctamine 1 (ANO1) and inhibited by Cl - channel blockers (NPPB and T16Ainh), enhanced the CBA (by 10-15%). The enhancement of the CBF and CBA stimulated by ABX was decreased to 50% by a Ca 2+ -free solution or nifedipine (an inhibitor of L-type Ca 2+ channels) and was abolished by BAPTA-AM in c-LAECs, indicating that an increase in [Ca 2+ ] i stimulated by ABX is essential for activating the pH pathway and the Cl - pathway. The enhancement of CBF and CBA enhanced by ABX was mimicked by applying a CO 2 /HCO 3 - -free Cl - -free solution, which increased the pH i and decreased the [Cl - ] i . In conclusion, ABX increased the CBF and CBA by 30% via the pH pathway and the Cl - pathway triggered by the [Ca 2+ ] i increase in c-LAECs of mice.