Skip to main content
. Author manuscript; available in PMC: 2022 Jul 1.
Published in final edited form as: Pharmacol Ther. 2021 Feb 15;223:107818. doi: 10.1016/j.pharmthera.2021.107818

Figure 2. Mechanisms of relaxation in airway smooth muscle (ASM).

Figure 2

Stimulation of β2-adrenergic and other receptors coupled to Gαs promotes ASM relaxation by activating adenylyl cyclase to generate cyclic adenosine monophosphate (cAMP). cAMP-dependent activation of protein kinase A (PKA) antagonizes Ca2+ signaling through several potential mechanisms. The exchange protein directly activated by cAMP (Epac) inhibits ASM proliferation. Methylxanthines such as theophylline increase cytosolic cAMP levels by inhibiting cAMP-degrading cyclic nucleotide phosphodiesterase (PDE) enzymes.