Protein kinase A-Iα regulates Na,K-ATPase endocytosis in alveolar epithelial cells exposed to high CO₂ concentrations

Elevated concentrations of CO₂ (hypercapnia) lead to alveolar epithelial dysfunction by promoting Na,K-ATPase endocytosis. In the present report, we investigated whether the CO₂/HCO₃^- activated soluble adenylyl cyclase (sAC) regulates this process. We found that hypercapnia increased the production of cyclic adenosine monophosphate (cAMP) and stimulated protein kinase A (PKA) activity via sAC, which was necessary for Na,K-ATPase endocytosis. During hypercapnia, cAMP was mainly produced in specific microdomains in the proximity of the plasma membrane, leading to PKA Type Ia activation. In alveolar epithelial cells exposed to high CO₂ concentrations, PKA Type Iα regulated the time-dependent phosphorylation of the actin cytoskeleton component α-adducin at serine 726. Cells expressing small hairpin RNA for PKAc, dominant-negative PKA Type Iα, small interfering RNA for α-adducin, and α-adducin with serine 726 mutated to alanine prevented Na,K-ATPase endocytosis. In conclusion, we provide evidence for a new mechanism by which hypercapnia via sAC, cAMP, PKA Type Iα, and α-adducin regulates Na, K-ATPase endocytosis in alveolar epithelial cells.