Which receptor subtype mediates vasodilation and bronchodilation in smooth muscle?

Which receptor subtype mediates vasodilation and bronchodilation in smooth muscle?

• A. Alpha-1 receptors
• B. Beta-1 receptors
• C. Alpha-2 receptors
• D. Beta-2 receptors

Answer: (D)

Beta-2 receptors mediate relaxation of smooth muscle, so they’re the ones that cause both vasodilation and bronchodilation. When activated, these receptors couple to Gs proteins to raise cAMP, which leads to smooth muscle relaxation by lowering intracellular calcium and reducing myosin light-chain kinase activity. This produces bronchodilation in the airways and vasodilation in certain vascular beds, like those supplying skeletal muscle. Other receptors don’t produce this combination: alpha-1 promotes vasoconstriction, beta-1 mainly affects heart rate and contractility, and alpha-2 inhibits norepinephrine release.

Beta-2 receptors mediate relaxation of smooth muscle, so they’re the ones that cause both vasodilation and bronchodilation. When activated, these receptors couple to Gs proteins to raise cAMP, which leads to smooth muscle relaxation by lowering intracellular calcium and reducing myosin light-chain kinase activity. This produces bronchodilation in the airways and vasodilation in certain vascular beds, like those supplying skeletal muscle. Other receptors don’t produce this combination: alpha-1 promotes vasoconstriction, beta-1 mainly affects heart rate and contractility, and alpha-2 inhibits norepinephrine release.