Urine exosomes from healthy and hypertensive pregnancies display elevated level of α-subunit and cleaved α- and γ-subunits of the epithelial sodium channel—ENaC

P170 The mineralocorticoid hormone, aldosterone increases renal tubule Na absorption via increases in the protein abundances of the α-subunit of the epithelial sodium channel (ENaC) and the 70 kDa form of the γ- subunit of ENaC (JCI 104:R19-R23). This study assesses the affect of dietary salt restriction on the regulation of the epithelial sodium channel (ENaC) in the lung and distal colon, in addition to kidney, using semiquantitative immunoblotting. Rats were placed initially on either a control Na intake (0.02 meq/day), or a low Na intake (0.2 meq/day) for 10 days. The low salt treated rats demonstrated an increase in plasma aldosterone levels at day 10 (control = 0.78 + 0.32 nM; Na restricted = 3.50 + 1.30 nM). In kidney homogenates, there were marked increases in the band density of the α-subunit of ENaC (286 % of control) and the 70 kDa form of γ-subunit of ENaC (262 % of control), but no increase in the abundance of the β-subunit of ENaC. In lung homogenates, there was no significant change in the band densities of the α, β, or γ subunits of ENaC. In distal colon, there was an increase in the band density of the β-subunit of ENaC (311 % of control) and an increase in both the 85 kDa (2355% of control) and 70 kDa (843 % of control) form of the γ subunit of ENaC in response to dietary Na restriction. However, there was no significant difference in the band density of the α-subunit of ENaC. These findings demonstrate tissue specific regulation of the three subunits of ENaC in response to dietary salt restriction.

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5′ Heterogeneity in epithelial sodium channel α-subunit mRNA leads to distinct NH2-terminal variant proteins

AJP Cell Physiology ◽

10.1152/ajpcell.1998.274.5.c1312 ◽

1998 ◽

Vol 274 (5) ◽

pp. C1312-C1323 ◽

Cited By ~ 43

Author(s):

Christie P. Thomas ◽

Scott Auerbach ◽

John B. Stokes ◽

Kenneth A. Volk

Keyword(s):

Sodium Channel ◽

Xenopus Oocytes ◽

Epithelial Sodium Channel ◽

Open Reading Frame ◽

Splice Sites ◽

Α Subunit ◽

Exon 2 ◽

Reading Frame ◽

Subunit Mrna ◽

Epithelial Sodium Channel Enac

The amiloride-sensitive epithelial sodium channel (ENaC) is composed of three subunits: α, β, and γ. The human α-ENaC subunit is expressed as at least two transcripts (N. Voilley, E. Lingueglia, G. Champigny, M. G. Mattei, R. Waldmann, M. Lazdunski, and P. Barbry. Proc. Natl. Acad. Sci. USA91: 247–251, 1994). To determine the origin of these transcripts, we characterized the 5′ end of the α-ENaC gene. Four transcripts that differ at their first exon were identified. Exon 1A splices to exon 2 to form the 5′ end of α-ENaC1, whereas exon 1B arises separately and continues into exon 2 to form α-ENaC2. Other variant mRNAs, α-ENaC3 and α-ENaC4, are formed by activating 5′ splice sites within exon 1B. Although α-ENaC3 and -4 did not change the open reading frame for α-ENaC, α-ENaC2 contains upstream ATGs that add 59 amino acids to the previous (α-ENaC1) protein. To address the significance of these isoforms, both proteins were expressed in Xenopus oocytes. The cRNA for each α-ENaC transcript when combined with β- and γ-ENaC cRNA reconstituted a low-conductance ion channel with amiloride-sensitive currents of similar characteristics. We have thus identified variant α-ENaC mRNAs that lead to functional ENaC peptides.

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