title: Cell surface expression and turnover of the alpha-subunit of the epithelial sodium channel.
abstract: The renal epithelial cell line A6, derived from Xenopus laevis, expresses epithelial Na(+) channels (ENaCs) and serves as a model system to study hormonal regulation and turnover of ENaCs. Our previous studies suggest that the alpha-subunit of Xenopus ENaC (alpha-xENaC) is detectable as 150- and 180-kDa polypeptides, putative immature and mature alpha-subunit heterodimers. The 150- and 180-kDa alpha-xENaC were present in distinct fractions after sedimentation of A6 cell lysate through a sucrose density gradient. Two anti-alpha-xENaC antibodies directed against distinct domains demonstrated that only 180-kDa alpha-xENaC was expressed at the apical cell surface. The half-life of cell surface-expressed alpha-xENaC was 24-30 h, suggesting that once ENaC matures and is expressed at the plasma membrane, its turnover is similar to that reported for mature cystic fibrosis transmembrane conductance regulator. No significant changes in apical surface expression of alpha-xENaC were observed after treatment of A6 cells with aldosterone for 24 h, despite a 5.3-fold increase in short-circuit current. This lack of change in surface expression is consistent with previous observations in A6 cells and suggests that aldosterone regulates ENaC gating and increases channel open probability.
authors.affiliation: Department of Medicine, University of Pittsburgh, Pittsburgh 15261, USA. kleyman@pitt.edu
authors.forename: T R
authors.initials: TR
authors.lastname: Kleyman
authors.forename: J B
authors.initials: JB
authors.lastname: Zuckerman
authors.forename: P
authors.initials: P
authors.lastname: Middleton
authors.forename: K A
authors.initials: KA
authors.lastname: McNulty
authors.forename: B
authors.initials: B
authors.lastname: Hu
authors.forename: X
authors.initials: X
authors.lastname: Su
authors.forename: B
authors.initials: B
authors.lastname: An
authors.forename: D C
authors.initials: DC
authors.lastname: Eaton
authors.forename: P R
authors.initials: PR
authors.lastname: Smith
mesh_terms: D000450:Aldosterone / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D016764:Cell Polarity; D002499:Centrifugation, Density Gradient; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D053503:Epithelial Sodium Channels; D015151:Immunoblotting; D007684:Kidney Tubules / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D011233:Precipitin Tests; D021122:Protein Subunits; D015222:Sodium Channels / Q000378:metabolism*; D013997:Time Factors; D019459:Urothelium / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D053503:Epithelial Sodium Channels; D021122:Protein Subunits; D015222:Sodium Channels; D000450:Aldosterone