Segmental variability of ENaC subunit expression in rat colon during dietary sodium depletion
Segmental variability of ENaC subunit expression in rat colon during dietary sodium depletion
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DOI：
10.1007/s00424-002-0828-7
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发表时间：
2002-07-01
影响因子：
4.5
通讯作者：
Sandle, GI
中科院分区：
文献类型：
--
作者：
Greig, ER;Baker, EH;Sandle, GI
在大鼠远端结肠，醛固酮对Na+通道（ENaC）α亚基水平的影响不大，但增加β和γ亚基的表达，并刺激产电Na+转运。相比之下，醛固酮不能刺激近端结肠的生电Na+转运的分子基础尚不清楚。因此，我们比较了继发于10天饮食Na+耗竭的醛固酮增多症对大鼠近端和远端结肠ENaC亚基表达的影响。北方分析显示，在对照组和Na+耗竭动物中，整个结肠中α亚基mRNA的水平相当且相似。相比之下，Na+耗竭显著增强远端结肠中β亚基mRNA的表达，但对近端结肠中β亚基mRNA的低表达水平没有影响。通过PCR评价的γ-亚基的表达也仅限于Na+耗竭动物的远端结肠。Western分析表明，两组动物的近端和远端结肠中的α-亚基蛋白水平相似，而β-亚基和γ-亚基蛋白仅或主要在Na+耗竭动物的远端结肠中检测到。免疫细胞化学证实，显着水平的所有三个亚基蛋白质只发生在顶端膜的表面细胞在远端结肠的Na+耗尽的动物。我们的研究结果是一致的，与以往的研究表明，醛固酮刺激产电Na+运输在大鼠远端结肠通过增加β-和γ-亚基mRNA和蛋白质的表达，从而在顶端域的功能异聚体ENaC蛋白的量。他们还表明，醛固酮不能刺激大鼠近端结肠中的生电Na+转运（尽管存在α亚基mRNA和蛋白质），因为其不能增强该区段中的β和γ亚基表达。
In rat distal colon, aldosterone has little effect on Na+ channel (ENaC) alpha-subunit levels but increases the expression of the beta- and gamma-subunits and stimulates electrogenic Na+ transport. By contrast, the molecular basis of aldosterone's inability to stimulate electrogenic Na+ transport in the proximal colon is unclear. We therefore compared the effects of hyperaldosteronism secondary to 10 days dietary Na+ depletion on ENaC subunit expression in rat proximal and distal colon. Northern analyses revealed appreciable and similar levels of a-subunit mRNA throughout the colon in control and Na+-depleted animals. By contrast, Na+ depletion substantially enhanced beta-subunit mRNA expression in the distal colon, but had no effect on the low expression levels of beta-subunit mRNA in the proximal colon. Expression of the gamma-subunit, evaluated by PCR, was also restricted to the distal colon of Na+-depleted animals. Western analyses demonstrated similar levels of a-subunit protein in the proximal and distal colon of both groups of animals, whereas beta-subunit and gamma-subunit proteins were detected solely or predominantly in the distal colon of the Na+-depleted animals. Immunocytochemistry confirmed that significant levels of all three subunit proteins only occurred in the apical membrane of surface cells in the distal colon of Na+-depleted animals. Our findings are consistent with previous studies demonstrating that aldosterone stimulates electrogenic Na+ transport in rat distal colon by increasing the expression of beta- and gamma-subunit mRNA and protein, and thus the amount of functional heteromeric ENaC protein in the apical domain. They also show that aldosterone is incapable of stimulating electrogenic Na+ transport in rat proximal colon (despite the presence of alpha-subunit mRNA and protein) because of its inability to enhance beta- and gamma-subunit expression in this segment.