Fig. 2.

Airways of Gaa^−/− mice are hyporesponsive to methacholine (MCh) in vivo. Forced oscillometry measures of respiratory and airway resistance in anesthetized and mechanically ventilated Gaa^−/− and WT mice are shown. Measurements were taken following incremental doses of nebulized MCh from 3.123 to 100 mg/ml. A: overall respiratory resistance (R_rs) in WT (n = 4) and Gaa^−/− (n = 6) mice. Initially, during saline administration no differences in overall resistance were appreciated between WT and Gaa^−/− mice, but with increasing doses, the resistance showed a more robust increase in WT mice compared with Gaa^−/− mice. B: Gaa^−/− mice have a central airway resistance (R_n) that is hyporesponsive to higher doses of MCh in compared with WT mice. C: finally, tissue damping (G), which is reflection of the smallest airways and tissue resistance, was also hyporesponsive to MCh in Gaa^−/− mice. *P ≤ 0.05, pair-wise comparison; #P ≤ 0.05, baseline comparison.