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 αβγ 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 αβγ ENaC in a dose- and external Na(+) concentration-dependent fashion. Intriguingly, cpt-cAMP activated human δβγ more potently than αβγ channels, suggesting that structural diversity in ectoloop between human α, δ, 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 (β(ΔV348) and γ(H233R)) 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 (αβ(S520C)γ) 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 αβγ and δβγ ENaC channels by relieving self-inhibition.
PubMed ID: 21419751
PMC ID: PMC3091966
Article link: Biochim Biophys Acta.
Grant support: HL095435 NHLBI NIH HHS , HL87017 NHLBI NIH HHS , R01 HL087017-01 NHLBI NIH HHS , R01 HL087017-02 NHLBI NIH HHS , R03 HL095435-01A1 NHLBI NIH HHS , R01 GM085237-02 NIGMS NIH HHS , R01 GM085237 NIGMS NIH HHS , R01 HL087017 NHLBI NIH HHS , R03 HL095435 NHLBI NIH HHS
Genes referenced: plg