Nitric oxide-dependent ethanol stimulation of ciliary motility is linked to cAMP-dependent protein kinase (PKA) activation in bovine bronchial epithelium

Background: The first line of protection in the lung from the outside envir onment is provided by the mucociliary apparatus, which continually clears t he airways of inhaled microorganisms, dust, and debris. Because alcohol is known to impair airway host defenses, we have examined the effects of ethan ol on mucociliary function. In earlier studies, we found that ethanol rapid ly and transiently stimulates ciliary motility through a nitric oxide-depen dent mechanism. Because many agonists stimulate ciliary motility through ac tivation of cyclic nucleotide-dependent protein kinases, we hypothesized th at ethanol stimulates ciliary motility by activating protein kinases. Methods: Protein kinase activity and ciliary beat frequency (CBF) were assa yed in primary cultures of bovine bronchial epithelial cells after exposure to ethanol. Results: Ethanol markedly activated cyclic adenosine monophosphate (cAMP)-d ependent protein kinase [protein kinase A (PKA)I at biologically relevant c oncentrations (20-100 mM), with activation detectable after 15 min and pers isting up to 4 kr. Ethanol's PKA activation was blocked by nitric oxide syn thase inhibitors, indicating a nitric oxide-dependent pathway, and was also specifically blocked by PKA. inhibitors. Ethanol did not directly activate cyclic guanosine monophosphate (cGMP)-dependent protein kinase [protein ki nase G (PKG)] in bovine bronchial epithelial cells, but inhibitors of PKG a ttenuated PKA activation, suggesting a link between PKA activation and PKG activation during ethanol exposure. CBF increased in parallel to PKA activa tion, suggesting tight coupling between stimulated CBF and PKA activation. Conclusion: We conclude that ethanol stimulates CBF through activating PKA in bovine bronchial epithelial cells and we suggest a cooperative mechanism involving PKA and nitric oxide.