Distinct Action of Flavonoids, Myricetin and Quercetin, on Epithelial Cl−Secretion: Useful Tools as Regulators of Cl−Secretion

Epithelial Cl − secretion plays important roles in water secretion preventing bacterial/viral infection and regulation of body fluid. We previously suggested that quercetin would be a useful compound for maintaining epithelial Cl − secretion at a moderate level irrespective of cAMP-induced stimulation. However, we need a compound that stimulates epithelial Cl − secretion even under cAMP-stimulated conditions, since in some cases epithelial Cl − secretion is not large enough even under cAMP-stimulated conditions. We demonstrated that quercetin and myricetin, flavonoids, stimulated epithelial Cl − secretion under basal conditions in epithelial A6 cells. We used forskolin, which activates adenylyl cyclase increasing cytosolic cAMP concentrations, to study the effects of quercetin and myricetin on cAMP-stimulated epithelial Cl − secretion. In the presence of forskolin, quercetin diminished epithelial Cl − secretion to a level similar to that with quercetin alone without forskolin. Conversely, myricetin further stimulated epithelial Cl − secretion even under forskolin-stimulated conditions. This suggests that the action of myricetin is via a cAMP-independent pathway. Therefore, myricetin may be a potentially useful compound to increase epithelial Cl − secretion under cAMP-stimulated conditions. In conclusion, myricetin would be a useful compound for prevention from bacterial/viral infection even under conditions that the amount of water secretion driven by cAMP-stimulated epithelial Cl − secretion is insufficient.