Effects of halothane and enflurane on epithelium-dependent contraction and ion transport of canine tracheal epithelium.

To gain insight into the cellular mechanisms involved in bronchodilation induced by inhalation anesthetics, we investigated whether halothane and enflurane can modulate functions of airway epithelium, such as epithelium-mediated bronchodilation and transepithelial transport. To measure the isometric tension of airways, paired rings of canine bronchi (4-6 mm OD), with and without the epithelium were mounted in Krebs-Ringer solution, gassed with 95% O2 and 5% CO2, and isometric tension was continuously recorded. To determine transepithelial transport, the posterior membranous portion of the trachea was mounted in Ussing-type chambers and the potential difference (PD), short-circuit current (SCC), and transepithelial resistance (R) were determined.Halothane and enflurane increased the contractile responses of the trachea to acetylcholine (ACh) in strips either with or without epithelium. However, this enhancement of the contractile responses by volatile agents was much larger with the epithelium than without. Furthermore, halothane tended to gradually increase and then decrease SCC of the trachea, but these changes were not statistically significant. These results indicate that halothane may modulate contractile response of the isolated trachea to ACh, but has no effect on ion transport by airway epithelium. The responsiveness of the trachea may be regulated independently of ion transport by airway epithelium.