Effect of cAMP on ciliary function in rabbit tracheal epithelial cells.

To study the effect of adenosine 3',5'-cyclic monophosphate (cAMP) on respiratory ciliary activity, we measured ciliary beat frequency (CBF) of rabbit tracheal epithelium by a photoelectric method in response to cAMP analogues and agents that can increase endogenous cAMP production. Addition of 8-bromo-cAMP dose dependently enhanced CBF, with the maximal increase and the concentration necessary to produce a half-maximal response (KD) being 31.0 +/- 3.4% (SE) (P less than 0.001) and 3.2 +/- 1.5 x 10(-7) M, respectively. Other structurally dissimilar cAMP analogues dibutyryl cAMP and chlorophenylthio-cAMP likewise caused increases in CBF. The phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine and the adenylate cyclase stimulator forskolin also augmented CBF in a dose-dependent fashion and were accompanied by the increases in intracellular concentrations of cAMP. Ciliary discoordination was not observed in any of the experiments. These results suggest that cAMP may accelerate mucociliary clearance through the activation of ciliary motility and that intracellular cAMP levels appear to be an important determinant for the lung mucociliary transport functions.