Role of acetylcholine and polyspecific cation transporters in serotonin-induced bronchoconstriction in the mouse.
BACKGROUND
It has been proposed that serotonin (5-HT)-mediated constriction of the murine trachea is largely dependent on acetylcholine (ACh) released from the epithelium. We recently demonstrated that ACh can be released from non-neuronal cells by corticosteroid-sensitive polyspecific organic cation transporters (OCTs), which are also expressed by airway epithelial cells. Hence, the hypothesis emerged that 5-HT evokes bronchoconstriction by inducing release of ACh from epithelial cells via OCTs.


METHODS
We tested this hypothesis by analysing bronchoconstriction in precision-cut murine lung slices using OCT and muscarinic ACh receptor knockout mouse strains. Epithelial ACh content was measured by HPLC, and the tissue distribution of OCT isoforms was determined by immunohistochemistry.


RESULTS
Epithelial ACh content was significantly higher in OCT1/2 double-knockout mice (42 +/- 10 % of the content of the epithelium-denuded trachea, n = 9) than in wild-type mice (16.8 +/- 3.6 %, n = 11). In wild-type mice, 5-HT (1 microM) caused a bronchoconstriction that slightly exceeded that evoked by muscarine (1 microM) in intact bronchi but amounted to only 66% of the response to muscarine after epithelium removal. 5-HT-induced bronchoconstriction was undiminished in M2/M3 muscarinic ACh receptor double-knockout mice which were entirely unresponsive to muscarine. Corticosterone (1 microM) significantly reduced 5-HT-induced bronchoconstriction in wild-type and OCT1/2 double-knockout mice, but not in OCT3 knockout mice. This effect persisted after removal of the bronchial epithelium. Immunohistochemistry localized OCT3 to the bronchial smooth muscle.


CONCLUSIONS
The doubling of airway epithelial ACh content in OCT1/2-/- mice is consistent with the concept that OCT1 and/or 2 mediate ACh release from the respiratory epithelium. This effect, however, does not contribute to 5-HT-induced constriction of murine intrapulmonary bronchi. Instead, this activity involves 1) a non-cholinergic epithelium-dependent component, and 2) direct stimulation of bronchial smooth muscle cells, a response which is partly sensitive to acutely administered corticosterone acting on OCT3. These data provide new insights into the mechanisms involved in 5-HT-induced bronchoconstriction, including novel information about non-genomic, acute effects of corticosteroids on bronchoconstriction.
Kummer
Wolfgang
W
Institute for Anatomy and Cell Biology, Justus-Liebig-University, 35385 Giessen, Germany. wolfgang.kummer@anatomie.med.uni-giessen.de
Wiegand
Silke
S
Akinci
Sibel
S
Wessler
Ignatz
I
Schinkel
Alfred H
AH
Wess
Jürgen
J
Koepsell
Hermann
H
Haberberger
Rainer V
RV
Lips
Katrin S
KS
D000109:Acetylcholine / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D001980:Bronchi / Q000187:drug effects* / Q000378:metabolism; D016084:Bronchoconstriction / Q000502:physiology*; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D009116:Muscarine / Q000494:pharmacology; D027701:Organic Cation Transport Proteins / Q000172:deficiency / Q000378:metabolism / Q000502:physiology*; D027702:Organic Cation Transporter 1 / Q000172:deficiency / Q000378:metabolism / Q000502:physiology*; D000075102:Organic Cation Transporter 2; D043585:Receptor, Muscarinic M2 / Q000172:deficiency; D043587:Receptor, Muscarinic M3 / Q000172:deficiency; D020545:Respiratory Mucosa / Q000378:metabolism / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology*; D014018:Tissue Distribution; D014132:Trachea / Q000378:metabolism
D027701:Organic Cation Transport Proteins; D027702:Organic Cation Transporter 1; D000075102:Organic Cation Transporter 2; D043585:Receptor, Muscarinic M2; D043587:Receptor, Muscarinic M3; C491012:Slc22a2 protein, mouse; D012701:Serotonin; D009116:Muscarine; D000109:Acetylcholine