Research

Role of acetylcholine and polyspecific cation transporters in serotonin-induced bronchoconstriction in the mouse

Wolfgang Kummer¹ , Silke Wiegand¹ , Sibel Akinci¹ , Ignatz Wessler² , Alfred H Schinkel³ , Jürgen Wess⁴ , Hermann Koepsell⁵ , Rainer V Haberberger^1,6 and Katrin S Lips¹

¹  Institute for Anatomy and Cell Biology, Justus-Liebig-University, 35385 Giessen, Germany

²  Department of Pathology, University of Mainz, Germany

³  Division of Experimental Therapy, The Netherlands Cancer Institute, 1066 CX Amsterdam, The Netherlands

⁴  Laboratory of Bioorganic Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892, USA

⁵  Institute for Anatomy and Cell Biology, Julius-Maximilians-University, 97070 Würzburg, Germany

⁶  Department of Anatomy and Histology, Flinders University, 50001 Adelaide, Australia

author email corresponding author email

Respiratory Research 2006, 7:65doi:10.1186/1465-9921-7-65

Published:	12 April 2006

Abstract

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 μM) caused a bronchoconstriction that slightly exceeded that evoked by muscarine (1 μM) 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 μM) 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.

Conclusion

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.