Luminal cholinergic signalling in airway lining fluid: a novel mechanism for activating chloride secretion via Ca²⁺-dependent Cl⁻ and K⁺ channels.
OBJECTIVE
Recent studies detected the expression of proteins involved in cholinergic metabolism in airway epithelial cells, although the function of this non-neuronal cholinergic system is not known in detail. Thus, this study focused on the effect of luminal ACh as a regulator of transepithelial ion transport in epithelial cells.


METHODS
RT-PCR experiments were performed using mouse tracheal epithelial cells for ChAT and organic cation transporter (OCT) transcripts. Components of tracheal airway lining fluid were analysed with desorption electrospray ionization (DESI) MS. Effects of nicotine on mouse tracheal epithelial ion transport were examined with Ussing-chamber experiments.


RESULTS
Transcripts encoding ChAT and OCT1-3 were detected in mouse tracheal epithelial cells. The DESI experiments identified ACh in the airway lining fluid. Luminal ACh induced an immediate, dose-dependent increase in the transepithelial ion current (EC₅₀: 23.3 µM), characterized by a transient peak and sustained plateau current. This response was not affected by the Na⁺-channel inhibitor amiloride. The Cl⁻-channel inhibitor niflumic acid or the K⁺-channel blocker Ba²⁺ attenuated the ACh effect. The calcium ionophore A23187 mimicked the ACh effect. Luminal nicotine or muscarine increased the ion current. Experiments with receptor gene-deficient animals revealed the participation of muscarinic receptor subtypes M₁ and M₃.


CONCLUSIONS
The presence of luminal ACh and activation of transepithelial ion currents by luminal ACh receptors identifies a novel non-neuronal cholinergic pathway in the airway lining fluid. This pathway could represent a novel drug target in the airways.
Institute of Animal Physiology, Justus-Liebig-University Giessen, Giessen, Germany.
Monika I
MI
Hollenhorst
Katrin S
KS
Lips
Miriam
M
Wolff
Jürgen
J
Wess
Stefanie
S
Gerbig
Zoltan
Z
Takats
Wolfgang
W
Kummer
Martin
M
Fronius
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D012634:Bodily Secretions / Q000378:metabolism; D050482:Catecholamine Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D018118:Chloride Channels / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002795:Choline O-Acetyltransferase / Q000235:genetics / Q000378:metabolism*; D018679:Cholinergic Agonists / Q000494:pharmacology; D015870:Gene Expression; D008564:Membrane Potentials / Q000187:drug effects; D049990:Membrane Transport Modulators / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D027701:Organic Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D027702:Organic Cation Transporter 1 / Q000235:genetics / Q000378:metabolism*; D000075102:Organic Cation Transporter 2; D024681:Potassium Channels, Calcium-Activated / Q000037:antagonists & inhibitors / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D043643:Receptor, Muscarinic M1 / Q000235:genetics / Q000378:metabolism; D043587:Receptor, Muscarinic M3 / Q000235:genetics / Q000378:metabolism; D020545:Respiratory Mucosa / Q000187:drug effects / Q000378:metabolism*; D014132:Trachea / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D000099254:Organic Cation Transporter 3
D000109:Acetylcholine; D050482:Catecholamine Plasma Membrane Transport Proteins; D018118:Chloride Channels; D002795:Choline O-Acetyltransferase; D018679:Cholinergic Agonists; D049990:Membrane Transport Modulators; D027701:Organic Cation Transport Proteins; D027702:Organic Cation Transporter 1; D000075102:Organic Cation Transporter 2; D024681:Potassium Channels, Calcium-Activated; D020033:Protein Isoforms; D043643:Receptor, Muscarinic M1; D043587:Receptor, Muscarinic M3; D000099254:Organic Cation Transporter 3; C103766:Slc22a1 protein, mouse; C491012:Slc22a2 protein, mouse