Objective: 

Acetylcholine (ACh) plays an important role as an auto/paracrine mediator besides its function as a neurotransmitter. There is increasing evidence for the presence of a non-neuronal cholinergic system in non-nervous tissues such as respiratory epithelia. The non-neuronal impact of ACh on tracheal epithelium is so far not investigated in detail. Thus the aim of this study was to characterize the influence of ACh on murine tracheal epithelium.

Methods: 

The impact of ACh on transepithelial ion current of freshly isolated tracheae of C57Bl/6 mice was investigated electrophysiologically with Ussing chamber recordings. For characterization of muscarinic receptors, M3^-/^- and M1^-/^- mice were used.

Results: 

Apical application of 100 mM ACh led to a current increase, consisting of a transient peak and a plateau value. Application of the ACh receptor agonists nicotine, DMPP and muscarine showed a contribution of nicotinic receptors located on the apical and the basolateral side of the epithelium and of muscarinic (M3 and M1) receptors. Experiments with the calcium ionophore A23187 revealed a dependency of the ACh-response on intracellular Ca²⁺-signaling. The ACh-effect could be blocked by application of the chloride channel inhibitor niflumic acid and the potassium channel inhibitor BaCl₂.

Conclusion: 

Taken together these data indicate that apically applied ACh acts on mouse tracheal epithelium in an auto/paracrine way, by increasing the intracellular calcium concentration after binding to nicotinic and muscarinic (M3 and M1) receptors. This in turn leads to an activation of an apical chloride and a basolateral potassium secretion and influences transepithelial ion transport.