M3 muscarinic acetylcholine receptor

Class

long-acting muscarinic antagonist (LAMA)

Pathway

blocks acetylcholine-mediated bronchial smooth-muscle contraction

The M3 muscarinic acetylcholine receptor is a G protein-coupled receptor expressed on airway smooth muscle, submucosal glands, and other tissues. When acetylcholine, released from parasympathetic nerve endings, binds M3 receptors on bronchial smooth muscle, it triggers contraction and narrows the airway; it also stimulates mucus secretion from submucosal glands. In chronic obstructive pulmonary disease and asthma, this cholinergic tone contributes to persistent airway narrowing and airflow limitation. Long-acting muscarinic antagonists (LAMAs) block acetylcholine from binding M3 receptors, allowing airway smooth muscle to relax and the airway lumen to widen, which improves airflow and reduces symptoms such as breathlessness. Because these agents bind receptors that also exist on other organs, notably the heart, gut, bladder, and eye, dosing and delivery are designed to concentrate the drug locally in the lungs after inhalation, limiting systemic exposure. The clinical value of this mechanism lies in providing sustained bronchodilation across obstructive airway diseases, often as a foundation therapy that can be combined with other bronchodilator classes acting through complementary receptor systems, such as beta-2 adrenergic agonists, to achieve broader relaxation of airway smooth muscle through independent signaling pathways.