Muscarinic acetylcholine receptor, subtype M3

Class

Long-acting muscarinic antagonist (LAMA)

Pathway

Cholinergic (acetylcholine) bronchoconstriction pathway

Notes

original target text: Muscarinic acetylcholine receptor, subtype M3 (airway smooth muscle/submucosal glands)

The M3 muscarinic acetylcholine receptor is a cell-surface protein found on airway smooth muscle and on the submucosal glands that line the bronchi. It is activated by acetylcholine, a neurotransmitter released from nerve endings of the parasympathetic (vagal) nervous system, which supplies continuous background tone to the airways. When acetylcholine binds M3, it triggers a signaling cascade that contracts the surrounding smooth muscle, narrowing the airway, and stimulates gland cells to secrete mucus. In diseases marked by chronic airflow limitation, particularly chronic obstructive pulmonary disease and asthma, this cholinergic tone contributes substantially to airway narrowing and excess mucus. Long-acting muscarinic antagonists (LAMAs) are small molecules that occupy the M3 receptor without activating it, blocking acetylcholine from binding and thereby relaxing airway smooth muscle and reducing gland secretion. Because these drugs are engineered to remain bound to M3 for an extended period, a single dose can sustain bronchodilation over many hours, supporting infrequent dosing. This mechanism addresses a fundamentally different contributor to airway obstruction than pathways involving inflammation or beta-adrenergic relaxation, making muscarinic blockade a complementary approach in managing chronic respiratory disease where cholinergic drive is a significant factor.