Cpt-Camp Activates Human Epithelial Sodium Channels Via Relieving Self-Inhibition
External Na+ self-inhibition is an intrinsic feature of epithelial sodium channels (ENaC). Cpt-cAMP regulates heterologous guinea pig but not rat Î±Î²Î³ ENaC in a ligand-gated manner. We hypothesized that cpt-cAMP may eliminate the self-inhibition of human ENaC thereby open channels. Regulation of self-inhibition by this compound in oocytes was analyzed using the two-electrode voltage clamp and Ussing chamber setups. External cpt-cAMP stimulated human but not rat and murine Î±Î²Î³ ENaC in a dose- and external Na+ concentration-dependent fashion. Intriguingly, cpt-cAMP activated human Î´Î²Î³ more potently than Î±Î²Î³ channels, suggesting that structural diversity in ectoloop between human Î±, Î´, and those ENaC of other species determines the stimulating effects of cpt-cAMP. Cpt-cAMP increased the ratio of stationary and maximal currents. Mutants having abolished self-inhibition (Î² Î”V348 and Î³H233R) almost completely eliminated cpt-cAMP mediated activation of ENaC. On the other hand, mutants both enhancing self-inhibition and elevating cpt-cAMP sensitivity increased the stimulating effects of the compound. This compound, however, could not activate already fully opened channels, e.g., degenerin mutation (Î±Î² S520CÎ³) and the proteolytically cleaved ENaC by plasmin. Cpt-cAMP activated native ENaC to the same extent as that for heterologous ENaC in human lung epithelial cells. Our data demonstrate that cpt-cAMP, a broadly used PKA activator, stimulates human Î±Î²Î³ and Î´Î²Î³ ENaC channels by relieving self-inhibition. Â© 2011 Elsevier B.V. All rights reserved.
Biochimica et Biophysica Acta - Biomembranes
Digital Object Identifier (DOI)
Molina, Raul; Han, Dong Yun; Su, Xue Feng; Zhao, Run Zhen; Zhao, Meimi; Sharp, Gretta M.; Chang, Yongchang; and Ji, Hong Long, "Cpt-Camp Activates Human Epithelial Sodium Channels Via Relieving Self-Inhibition" (2011). Neurobiology. 46.