Cordyceps militaris extract stimulates Cl− secretion across human bronchial epithelia by both Ca2+- and cAMP-dependent pathways

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Ethnopharmacological relevanceThe caterpillar fungus Cordyceps militaris (CM; Clavicipitaceae) is a well-known traditional Chinese medicine that can be artificially cultivated on a large scale. We have previously demonstrated that its stimulatory action on ion transport in human airway epithelia is similar to Cordyceps sinensis (Clavicipitaceae), which has been traditionally used to treat respiratory diseases. Aim of the studyTo investigate the signal transduction mechanism(s) underlying CM-induced ion transport activity in cultured human bronchial epithelia. Materials and methods16HBE14o-, a human bronchial epithelial cell line, was used to study the regulation of ion transport by the water extract of CM. CM extract was added to the apical or basolateral aspect of the epithelia. In subsequent experiments, different Cl− channel and K+ channel blockers, adenylate cyclase and protein kinase A (PKA) inhibitors, and an intracellular Ca2+ chelator were used to examine the involvement of apical Cl− and basolateral K+ channels in mediating CM-induced Cl− secretion and the underlying signal transduction mechanism(s). PKA activity was also measured in 16HBE14o- cells. ResultsCM stimulated Cl− secretion across 16HBE14o- monolayers in a dose-dependent manner. Cl− secretion could be inhibited by apical application of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl−channel blocker and the calcium-activated Cl− channel (CaCC) blocker. Cl− secretion was sensitive to basolateral application of different K+ channel blockers. Similar inhibitory patterns were obtained in nystatin-permeabilized epithelia. The CM-induced Cl− secretion could be inhibited by adenylate cyclase and PKA inhibitors as well as an intracellular Ca2+ chelator. Data from the PKA assay suggested that CM extract caused a significant increase in PKA activity compared with untreated control epithelia. ConclusionsThese results suggest that CM extract stimulated Cl− secretion across human bronchial epithelia, possibly via apical CFTR and CaCC, and the basolateral K+ channels are involved in driving apical Cl− exit. The underlying signal transduction mechanisms involve both cAMP- and Ca2+-dependent pathways.