Functional expression of a pseudohypoaldosteronism type I mutated epithelial Na+ channel lacking the pore-forming region of its α subunit
Olivier Bonny, … , Jean-Daniel Horisberger, Bernard C. Rossier
Olivier Bonny, … , Jean-Daniel Horisberger, Bernard C. Rossier
Published October 1, 1999
Citation Information: J Clin Invest. 1999;104(7):967-974. https://doi.org/10.1172/JCI6821.
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Article

Functional expression of a pseudohypoaldosteronism type I mutated epithelial Na+ channel lacking the pore-forming region of its α subunit

Abstract

The autosomal recessive form of type I pseudohypoaldosteronism (PHA-I) is an inherited salt-losing syndrome resulting from diminution-of-function mutations in the 3 subunits of the epithelial Na+ channel (ENaC). A PHA-I stop mutation (αR508stop) of the ENaC α subunit is predicted to lack the second transmembrane domain and the intracellular COOH-terminus, regions of the protein involved in pore function. Nonetheless, we observed a measurable Na+ current in Xenopus laevis oocytes that coexpress the β and γ subunits with the truncated α subunit. The mutant α was coassembled with β and γ subunits and was present at the cell surface at a lower density, consistent with the lower Na+ current seen in oocytes with the truncated α subunit. The single-channel Na+ conductance for the mutant channel was only slightly decreased, and the appearance of the macroscopic currents was delayed by 48 hours with respect to wild-type. Our data suggest novel roles for the α subunit in the assembly and targeting of an active channel to the cell surface, and suggest that channel pores consisting of only the β and γ subunits can provide significant residual activity. This activity may be sufficient to explain the absence of a severe pulmonary phenotype in patients with PHA-I.

Authors

Olivier Bonny, Ahmed Chraibi, Jan Loffing, Nicole Fowler Jaeger, Stefan Gründer, Jean-Daniel Horisberger, Bernard C. Rossier

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Figure 1

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α ENaC subunit truncations reported in recessive PHA-I. Primary structur...
α ENaC subunit truncations reported in recessive PHA-I. Primary structure of wild-type (WT) and predicted deletions of α subunits are illustrated. M1 and M2 denote first and second transmembrane domains; P denotes the pre-M2 domain of the second transmembrane domain. CRB1 and CRB2 stand for cysteine-rich boxes 1 and 2. Both deletion mutations reported for patients with PHA-I (human αR508stop and human αI68fr) predict an interruption of the α subunit before the M2 and the M1 membrane-spanning domains, respectively.