Figure 1.

Role of ACh and muscarinic receptors in the lung.

Notes: Data from these studies.¹¹,¹⁷ In large airways, ACh released from cholinergic nerves activates M₃ receptors on ASM, causing bronchoconstriction. In peripheral airways, where cholinergic nerves are absent, inflammatory cells stimulate epithelial cells to release ACh, activating M₃ receptors on ASM and causing bronchoconstriction. M₃ muscarinic receptors are shown as solid blue circles. For simplicity, other types of muscarinic receptor are not shown.

Abbreviations: ACh, acetylcholine; ASM, airway smooth muscle; CNS, central nervous system.