263 EX VIVO ANALYSIS OF AIRWAY CONTRACTION AND RELAXATION BY A β-AGONIST

Purpose A fundamental feature of asthma is an enhanced contractile response to stimuli. Given the physiological interplay between airway epithelia and smooth muscle cells, cell culture model systems are of limited utility in defining functionally relevant mechanisms impacting airway contraction and relaxation. We have established a lung explant culture system that retains contractile characteristics of intact airways. Methods Tracheal rings (˜ 4 mm) were isolated from Sprague-Dawley rats. Viability of explants was confirmed by microscopic observation of ciliary beating prior to treatment and by contractile response to 90 mM KCl after treatment. Explants were contracted using 2.5 μM methacholine (MCh) followed by relaxation using 100 μM isoproterenol (Iso) or 1 mM 8-Br-cAMP. Airway responsiveness was assessed by measuring the cross sectional area of the lumen using time-lapse video microscopy. Results Explants from 6 animals were analyzed and the cross sectional area expressed as percent reduction in the area at baseline. Mean (SD) sustained contractility of all explants following MCh was 21(11)% (n = 47). Subsequent addition of Iso and 8-Br-cAMP significantly reversed contraction by 14% (n = 21) and 52% (n = 15), respectively. 8-Br-cAMP induced relaxation was significantly better than that by Iso. Repetitive treatment with Iso at 30-minute intervals following Mch-induced contractility demonstrated tolerance to the relaxing effect of Iso. Conclusion Ex vivo cultures of rat airways can be utilized as a model to study mechanisms for relaxing hyperresponsive airways. This model provides an intact airway system that can be used to study interaction between airway smooth muscle and epithelial cells to better understand airway disease.