Absence of airway tone in BALB/c mice

An important determinant of airway function in humans is vagal-mediated cholinergic tone in airway smooth muscle (ASM). This airway tone may be altered in disease states. The use of mouse models for the study of airway diseases, including asthma, pulmonary fibrosis and COPD is well established. However, it is not known whether mice actually possess basal ASM tone or, if it does exist, how this tone changes in disease models. This study was undertaken to determine whether mice have detectable ASM tone in vivo.

Methods: Respiratory system impedance (Zrs) was measured in female adult BALB/c mice using a wave-tube modification of the forced oscillation technique. Zrs was measured during slow (~35 s) inflation-deflation manoeuvres between the transrespiratory pressures of 0 and 20 cmH2O. Baseline lung mechanics and thoracic lung volumes (TGV) were measured before and after each mouse was allocated to one of four treatment groups: ‘saline’ mice received an i.p injection of saline, ‘atropine’ mice received i.p. atropine sulphate, ‘vagotomy’ mice had their left and right cervical vagus nerves isolated by blunt dissection and cut, and ‘sham’ mice had the area of the vagus nerves exposed but the nerves were not cut.

Results:There were no post-treatment changes in TGV, airway resistance, tissue damping, tissue elastance, inertance or tissue hysteresivity in any of the four groups.

Conclusions: The lack of change in lung mechanics post-atropine or postvagotomy in BALB/c mice suggests that, unlike humans and many other species, the airways of mice have no baseline ASM tone.