Submitted on July 20, 2005
Accepted on March 1, 2006
A novel bronchial ring bioassay for the evaluation of small airway smooth muscle function in mice
John Q Liu1, Dennis Yang1, and Rodney J. Folz1*
1 Medicine, Duke University Medical Center, Durham, North Carolina, United States
* To whom correspondence should be addressed. E-mail: rodney.folz{at}duke.edu.
Advances in our understanding of murine airway physiology have been hindered by the lack of suitable, ex vivo, small airway bioassay systems. In this study, we introduce a novel small murine airway bioassay system that permits the physiologic and pharmacologic study of intrapulmonary bronchial smooth muscle via a bronchial ring preparation utilizing bronchial ring (BR) segments as small as 200 µm in diameter. Using this ex vivo BR bioassay, we characterized small airway smooth muscle contraction and relaxation in the presence and absence of bronchial epithelium. In control BRs, the application of mechanical stretch is followed by spontaneous bronchial smooth muscle relaxation. BRs pre-treated with methacholine (MCh) partially attenuate this stretch-induced relaxation by as much as 42% compared to control. MCh elicited a dose-dependent bronchial constriction with a maximal tension (Emax) of 8.7 ± 0.2 mN at an EC50 of 0.33 ± 0.02 µM. In the presence of nifedipine, ryanodine, 2-APB and SKF-96365, Emax to MCh was significantly reduced. In epithelium denuded BRs, MCh-induced contraction was significantly enhanced to 11.4 ± 1.0 mN with an EC50 of 0.16 ± 0.04 µM (p<0.01). Substance P relaxed MCh pre-contracted BR by 62.1%; however, this bronchial relaxation effect was completely lost in epithelium-denuded BRs. Papaverine virtually abolished MCh-induced constriction in both epithelium-intact and epithelium-denuded bronchial smooth muscle. In conclusion, this study introduces a novel murine small airway BR bioassay that allows for the physiologic study of smooth muscle airway contractile responses that may aid in our understanding of the pathophysiology of asthma.
