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-subunit of the
epithelial sodium channel
1 Department of Medicine, University of Pittsburgh, Pittsburgh 15261; 2 Department of Medicine, Maine Medical Center, Portland, Maine 04102; 3 Department of Physiology, Emory University, Atlanta, Georgia 30322; 4 Department of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104; and 5 Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, Alabama 35294
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
-subunit of Xenopus ENaC (
-xENaC)
is detectable as 150- and 180-kDa polypeptides, putative immature and
mature
-subunit heterodimers. The 150- and 180-kDa
-xENaC were present in distinct fractions after
sedimentation of A6 cell lysate through a sucrose density gradient. Two
anti-
-xENaC antibodies directed against distinct domains
demonstrated that only 180-kDa
-xENaC was expressed at
the apical cell surface. The half-life of cell surface-expressed
-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
-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.
epithelial sodium transport; epithelial sodium channels; ion channel; renal epithelium
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