β2-adrenergic regulation of ciliary beat frequency in rat bronchiolar epithelium: potentiation by isosmotic cell shrinkage

摘要

Single bronchiolar ciliary cells were isolated from rat lungs. The β2-adrenergic regulation of ciliary beat frequency (CBF) was studied using video-optical microscopy. Terbutaline (a β2-adrenergic agonist) increased CBF in a dose-dependent manner, and it also decreased the volume of the ciliary cells. These terbutaline actions were inhibited by a PKA inhibitor (H-89) and mimicked by forskolin, IBMX and DBcAMP. Ion transport inhibitors were used to isosmotically manipulate the volume of the terbutaline-stimulated bronchiolar ciliary cells. Amiloride (1 μm) and bumetanide (20 μm) potentiated cell shrinkage and the CBF increase, and they shifted the terbutaline dose–response curve to the lower-concentration side. Quinidine (500 μm), in contrast, increased cell volume and suppressed the CBF increase. Moreover, a KCl solution containing amiloride (1 μm) and strophanthidin (100 μm) increased cell volume and suppressed the CBF increase, and then the subsequent removal of either amiloride or strophanthidin decreased cell volume and further increased CBF. NPPB (10 μm) or glybenclamide (200 μm) had no effect on the action of terbutaline. Thus, in terbutaline-stimulated ciliary cells, cell shrinkage enhances the CBF increase; in contrast, cell swelling suppresses it. However, the results of direct manupulation of cell volume by applying osmotic stresses (hyperosmotic shrinkage or hyposmotic swelling) were the opposite of the findings of the isosmotic experiments: hyposmotic cell swelling enhanced the CBF increase, while isosmotic swelling suppressed it. These results suggest that isosmotic and non-isosmotic volume changes in terbutaline-stimulated bronchiolar ciliary cells may trigger different signalling pathways. In conclusion, terbutaline increases CBF and decreases the volume of rat bronchiolar ciliary cells via cAMP accumulation under isosmotic conditions, and the isosmotic cell shrinkage enhances the CBF increase by increasing cAMP sensitivity.