Figure 5.

Compartmentalized cAMP-signaling elements on the extracellular and intracellular surfaces of the apical cell membrane. Model depicts how diverse physical stimuli (e.g., hypotonicity and shear stress) regulate CFTR. After release of ATP onto the extracellular surface, Ado is generated by ectonucleotidases (NT). A_2B receptors bind Ado and activate AC present in the apical membrane by means of G_s. Sufficient cAMP is generated locally to activate PKA in a diffusionally restricted apical microdomain, but not in other cellular compartments. AKAP, A-kinase anchoring protein.