What is the mechanism of action of albuterol?

Albuterol is a selective Beta-2 adrenergic agonist (SABA — short-acting beta agonist). It stimulates β2-receptors on bronchial smooth muscle → increases cAMP → smooth muscle relaxation → bronchodilation. It's used for acute bronchospasm in asthma. A beta-2 ANTAgonist would cause bronchoconstriction. Ipratropium is the muscarinic antagonist bronchodilator.