Liddle’s syndrome mutations disrupt cAMP-mediated translocation of the epithelial Na+ channel to the cell surface
Peter M. Snyder
Peter M. Snyder
Published January 1, 2000
Citation Information: J Clin Invest. 2000;105(1):45-53. https://doi.org/10.1172/JCI7869.
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Article

Liddle’s syndrome mutations disrupt cAMP-mediated translocation of the epithelial Na+ channel to the cell surface

Abstract

The epithelial Na+ channel (ENaC) plays a critical role in Na+ absorption, and mutations in this channel cause diseases of Na+ homeostasis, including a genetic form of hypertension (Liddle’s syndrome). To investigate cAMP-mediated stimulation of ENaC, α, β, and γENaC were coexpressed in Fischer rat thyroid epithelia to generate apical Na+ channels and transepithelial Na+ current. cAMP agonists stimulated Na+ current by 70%. Following covalent modification of cysteines introduced into ENaC, cAMP increased the rate of appearance of unmodified channels at the cell surface. In addition, cAMP increased the fluorescent labeling of ENaC at the apical cell surface. Inhibition of vesicle trafficking by incubating epithelia at 15°C prevented the cAMP-mediated stimulation of ENaC. These results suggest that cAMP stimulates Na+ absorption in part by increasing translocation of ENaC to the cell surface. Stimulation of ENaC by cAMP was dependent on a sequence (PPPXY) in the COOH terminus of each subunit. This sequence is the target for mutations that cause Liddle’s syndrome, suggesting that cAMP-mediated translocation of ENaC to the cell surface is defective in this genetic form of hypertension.

Authors

Peter M. Snyder

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Figure 4

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Na+ current is inhibited by cAMP after covalent modification of βS520C. ...
Na+ current is inhibited by cAMP after covalent modification of βS520C. (a) Representative time course of current in epithelia expressing wild-type α and γhENaC with βS520C. MTSET (1 mM, filled) and cAMP agonists (open bars) were added to the apical membrane (bars). Epithelia were treated with MTSET, washed, and then treated (left) or not treated (right) with cAMP agonists. ISC stimulated by a second treatment with MTSET (downward arrow) was then determined. (b) Plot of cAMP-induced change in ISC following removal of MTSET (relative to the current change by MTSET; mean ± SEM, n = 5–8) for epithelia expressing either γG536C or βS520C with the other 2 wild-type subunits. (c) Plot of ISC (mean ± SEM, n = 5–6) stimulated by second treatment with MTSET (downward arrow in a) in cells treated or not treated with cAMP agonists, as indicated. *P < 0.003. (d) Model showing ENaC at plasma membrane and in an intracellular pool. MTSET irreversibly stimulates ENaC at the cell surface (black). The predicted response if cAMP increases ENaC translocation to the cell surface is shown.