Pharmacology of Airway Control Quiz

See Short-Acting β2 Agonists (SABAs). Option E is correct because short-acting beta2 agonists (SABAs) such as salbutamol and terbutaline stimulate Gs-coupled beta2 receptors on airway smooth muscle. A G-protein-coupled receptor passes its message through a G protein inside the cell, and the Gs type stimulates the enzyme adenylyl cyclase. This raises intracellular cyclic AMP (cAMP), which causes the smooth muscle to relax, so the airways widen and bronchodilation follows. Onset is within minutes and the effect lasts 4 to 6 hours, which suits their use as relievers for symptoms, in acute exacerbations (often by nebuliser) and before exercise. Side effects come mainly from beta2 stimulation in other tissues: tremor from skeletal muscle, palpitations and tachycardia, hypokalaemia (beta2 stimulation drives potassium into cells, which is why nebulised salbutamol is used in hyperkalaemia), hyperglycaemia and, at high doses, lactic acidosis. Frequent SABA use is a marker of poor asthma control. A memory aid: beta2 plus Gs means more cAMP and a relaxed airway.

• Receptor: short-acting beta2 agonists stimulate Gs-coupled beta2 receptors on airway smooth muscle.
• Pathway: Gs activates adenylyl cyclase, which raises cAMP and relaxes the muscle.
• Timing: onset within minutes and effect lasting 4 to 6 hours, so they are relievers.
• Side effects: tremor, tachycardia and hypokalaemia from beta2 stimulation in other tissues.