title: Cpt-cAMP activates human epithelial sodium channels via relieving self-inhibition.
abstract: 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.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center at Tyler, TX, USA.
authors.forename: Raul
authors.initials: R
authors.lastname: Molina
authors.forename: Dong-Yun
authors.initials: DY
authors.lastname: Han
authors.forename: Xue-Feng
authors.initials: XF
authors.lastname: Su
authors.forename: Run-Zhen
authors.initials: RZ
authors.lastname: Zhao
authors.forename: Meimi
authors.initials: M
authors.lastname: Zhao
authors.forename: Gretta M
authors.initials: GM
authors.lastname: Sharp
authors.forename: Yongchang
authors.initials: Y
authors.lastname: Chang
authors.forename: Hong-Long
authors.initials: HL
authors.lastname: Ji
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000494:pharmacology; D004563:Electrochemistry; D062708:Epithelial Sodium Channel Agonists; D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels / Q000235:genetics; D005260:Female; D006801:Humans; D051379:Mice; D016297:Mutagenesis, Site-Directed; D051381:Rats; D013873:Thionucleotides / Q000494:pharmacology*; D014982:Xenopus laevis
chemical_list: D062708:Epithelial Sodium Channel Agonists; D062686:Epithelial Sodium Channel Blockers; D053503:Epithelial Sodium Channels; D013873:Thionucleotides; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D000242:Cyclic AMP