ADRB2 and Airway obstruction: Airway diameter is regulated by contraction of ASM and enhanced ASM contraction leads to increased airway resistance, a feature of obstructive airway conditions such as COPD.26,27 Increased cholinergic tone is the main reversible component of airway obstruction in COPD,28–31 therefore, it is of interest to understand the mechanisms underlying cholinergic contractions of ASM and how they are targeted by β-AR agonists.