Enhancement of ciliary beat frequency induced by [Cl − ] i decrease in rat distal airway ciliary cells

Regulation of ciliary beat frequency (CBF) plays a key role in the maintenance of mucociliary clearance, which is a host defense mechanism of lungs. A previous report has shown that cell shrinkage enhances terbutaline (Tb, a β2‐adrenergic agonist)‐stimulated CBF. As an isosmotic cell shrinkage causes a decrease in the intracellular chloride ion concentration ([Cl − ] i ), we examined the effects of an [Cl − ] i decrease on the CBF enhancement. [Material and method] Ciliary cells in the distal airway of rat were isolated by an elastase treatment, and their CBFs were measured using a high speed camera. [Results] The application of Cl − ‐free solution or bumetanide, which decreased the [Cl − ] i , increased CBF and enhanced the Tb‐stimulated CBF. The application of 5‐nitro‐2‐(3‐phenylpropylamino) benzoic acid (NPPB), which increased the [Cl − ] i , decreased CBF, however it did not suppress the Tb‐stimulated CBF. An inhibitor of PKA (H89) decreased CBF to 40% and eliminated the enhancement of CBF induced by the Cl − ‐free solution and the Tb (10 μM). [Conclusion] A decrease in [Cl − ] i enhanced CBF by modulating PKA signalings.