ATP regulation of ciliary beat frequency in rat tracheal and distal airway epithelium

Ciliary beat frequency (CBF) was measured by video-optical microscopy in rat tracheal and distal airway ciliary cells using a slice preparation. In tracheal ciliary cells ( tracheal slice), ATP or 2-methylthio ATP ( MeSATP) increased CBF, which was inhibited by suramin ( 100 mu M, an inhibitor of purinergic receptor). Ionomycin ( 5 mu M) or thapsigargin ( 2 mu M) increased CBF similarly. Ca2+-free solution or addition of Ni2+ ( 1 mM) decreased CBF gradually by approximately 25% and subsequent stimulation with ATP ( 10 mu M) increased CBF transiently. The purinergic agonist experiments demonstrated that ATP increases CBF in tracheal ciliary cells via both P2X and P2Y receptors. ATP increased the intracellular calcium concentration ([Ca2+](i)) in tracheal ciliary cells. However, in distal airway ciliary cells ( lung slice), ATP did not increase CBF and [Ca2+](i), although a Ca2+- free solution decreased CBF, and ionomycin ( 5 mu M) or thapsigargin ( 2 mu M) increased it. Moreover, acetylcholine ( 100 mu M) did not increase CBF in distal airway ciliary cells, although it increased CBF in tracheal ciliary cells. Terbutaline ( 10 mu M), a selective beta(2)-adrenergic agonist, increased CBF in both tracheal and distal airway ciliary cells. These observations suggest that the Ca2+- mobilization mechanisms via purinergic or muscarinic receptors of the distal airway ciliary cell may be different from those of the tracheal ciliary cell. In conclusion, the CBF increase is differently regulated in the tracheal and distal airway epithelia of the rat.