Airway Smooth Muscle Sensitivity to Methacholine in Precision-Cut Lung Slices (PCLS) from Ovalbumin-induced Asthmatic Mice

Asthma is a chronic inflammatory disease characterized by airway hyperresponsiveness (AHR) and reversible airway obstruction. Methacholine (MCh) is widely used in broncho-provocation test to evaluate airway resistance. For experimental investigation, ovalbumin-induced sensitization is frequently used in rodents (Ova-asthma). However, albeit the inflammatory histology and AHR in vivo, it remains unclear whether the MCh sensitivity of airway smooth muscle isolated from Ova-asthma is persistently changed. In this study, the contractions of airways in precision-cut lung slices (PCLS) from control, Ova-asthma, and IL-13 overexpressed transgenic mice (IL-13TG) were compared by analyzing the airway lumen space (AW). The airway resistance in vivo was measured using plethysmograph. AHR and increased inflammatory cells in BAL fluid were confirmed in Ova-asthma and IL-13TG mice. In the PCLS from all three groups, MCh concentration-dependent narrowing of airway lumen (${\Delta}AW$) was observed. In contrast to the AHR in vivo, the $EC_{50}$ of MCh for ${\Delta}AW$ from Ova-asthma and IL-13TG were not different from control, indicating unchanged sensitivity to MCh. Although the AW recovery upon MCh-washout showed sluggish tendency in Ova-asthma, the change was also statistically insignificant. Membrane depolarization-induced ${\Delta}AW$ by 60 mM $K^+$ (60K-contraction) was larger in IL-13TG than control, whereas 60K-contraction of Ova-asthma was unaffected. Furthermore, serotonin-induced ${\Delta}AW$ of Ova-asthma was smaller than control and IL-13TG. Taken together, the AHR in Ova-asthma and IL-13TG are not reflected in the contractility of isolated airways from PCLS. The AHR of the model animals seems to require intrinsic agonists or inflammatory microenvironment that is washable during tissue preparation.