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A long isoform of the epithelial sodium channel alpha subunit forms a highly active channel.

ABSTRACT: A long isoform of the human Epithelial Sodium Channel (ENaC) ? subunit has been identified, but little data exist regarding the properties or regulation of channels formed by ?728. The baseline whole cell conductance of oocytes expressing trimeric ?728?? channels was 898.1±277.2 and 49.59±13.2 µS in low and high sodium solutions, respectively, and was 11 and 2 fold higher than the conductances of ?669?? in same solutions. ?728?? channels were also 2 to 5 fold less sensitive to activation by the serine proteases subtilisin and trypsin than ?669?? in low and high Na+ conditions. The long isoform exhibited lower levels of full length and cleaved protein at the plasma membrane and a rightward shifted sensitivity to inhibition by increases of [Na+]i. Both channels displayed similar single channel conductances of 4 pS, and both were activated to a similar extent by reducing temperature, altogether indicating that activation of baseline conductance of ?728?? was likely mediated by enhanced channel activity or open probability. Expression of ?728 in native kidneys was validated in human urinary exosomes. These data demonstrate that the long isoform of ?ENaC forms the structural basis of a channel with different activity and regulation, which may not be easily distinguishable in native tissue, but may underlie sodium hyperabsorption and salt sensitive differences in humans.

SUBMITTER: Berman JM

PROVIDER: S-EPMC4594420 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature

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A long isoform of the epithelial sodium channel alpha subunit forms a highly active channel.

Berman Jonathan M JM Brand Cristin C Awayda Mouhamed S MS

Channels (Austin, Tex.) 20150203 1

A long isoform of the human Epithelial Sodium Channel (ENaC) α subunit has been identified, but little data exist regarding the properties or regulation of channels formed by α728. The baseline whole cell conductance of oocytes expressing trimeric α728βγ channels was 898.1±277.2 and 49.59±13.2 µS in low and high sodium solutions, respectively, and was 11 and 2 fold higher than the conductances of α669βγ in same solutions. α728βγ channels were also 2 to 5 fold less sensitive to activation by the ...[more]

PMID: 25517724

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Project description:BackgroundThe amiloride-sensitive Epithelial Sodium Channel (ENaC) is critical in maintaining Na+ balance, extracellular fluid volume and long term blood pressure control. ENaC is composed of three main subunits alpha, beta, & gamma. While alpha ENaC is critical for channel functionality, beta & gamma ENaC maximize channel function. To date, there are four alternatively spliced forms of the alpha subunit of ENaC (alpha ENaC-a, -b, -c, & -d) that have been published in rats, in addition to the major alpha ENaC transcript. While alpha ENaC-a, -c & -d transcripts are low abundance transcripts compared to full-length alpha ENaC, alpha ENaC-b is a higher abundance and salt-sensitive transcript compared to full-length alpha ENaC.Presentation of the hypothesisalpha ENaC-b protein, which is preferentially produced in Dahl R rats, to a greater extent on high salt diet, exerts a dominant negative effect on full-length alpha ENaC subunit by physically binding to and trapping full-length alpha ENaC subunit in the endoplasmic reticulum, and finally accelerating full-length alpha ENaC proteolytic degradation in a dose-dependent manner.Testing the hypothesis1) To examine the mRNA and protein abundance of alpha ENaC-b relative to alpha ENaC full-length in kidney, lung, and taste tissues of Dahl rats. 2) To compare the expression (mRNA and protein) of alpha ENaC-b in kidneys of Dahl S and R rats on regular and high salt diet. 3) To examine the putative binding of alpha ENaC-b proteins to full-length alpha ENaC in vitro and to determine the impact of such binding on full-length alpha ENaC expression in vitro.Implications of the hypothesisOur studies will be the first to demonstrate the over-expression of salt-sensitive alpha ENaC-b spliced form in kidney tissues of Dahl R rats at the expense of full-length alpha ENaC. The current proposal will provide highly novel insights into the putative mechanisms leading to ENaC hypoactivity in high-salt-fed Dahl R rats. Finally, findings from the present proposal will uncover a new mechanism by which alternative splicing may control the regulation of ENaC expression/function.

Dataset Information

A long isoform of the epithelial sodium channel alpha subunit forms a highly active channel.

Publications

A long isoform of the epithelial sodium channel alpha subunit forms a highly active channel.

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