Category: signaling
Bronchial smooth-muscle tone balances bronchoconstriction against bronchodilation. CONSTRICTORS: vagal acetylcholine → M3 muscarinic → Gq → PLC → IP3/Ca²⁺ → contraction + mucus; cysteinyl-leukotrienes (LTD4) → CysLT1; histamine. DILATORS: β2-adrenoceptor → Gs → adenylate cyclase → cAMP → PKA → relaxation. Therapeutics map onto these: β2 agonists — short-acting salbutamol (rescue), long-acting salmeterol / formoterol / vilanterol (maintenance); antimuscarinics — short-acting ipratropium, long-acting tiotropium (COPD mainstay); methylxanthine theophylline + PDE4 inhibitor roflumilast raise cAMP / cut inflammation; CysLT1 antagonist montelukast; and inhaled corticosteroids (budesonide, fluticasone) suppress the upstream eosinophilic inflammation that drives bronchial hyperreactivity. Cross-links: beta_2, muscarinic, cyslt1, pde4, asthma_th2_eosinophil_inflammation.