Regulation of ENaC-mediated sodium transport by glucocorticoids in Reissner's membrane epithelium
Regulation of ENaC-mediated sodium transport by glucocorticoids in Reissner's membrane epithelium
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DOI：
10.1152/ajpcell.00338.2008
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发表时间：
2009-03-01
影响因子：
5.5
通讯作者：
Marcus, Daniel C.
中科院分区：
文献类型：
--
作者：
Kim, Sung Huhn;Kim, Kyunghee X.;Marcus, Daniel C.
Kim SH，Kim KX，Raveendran NN，Wu T，Pondugula SR，Marcus DC. Reissner膜上皮糖皮质激素对ENaC介导的钠转运的调节美国生理学杂志细胞生理学296：C544-C557，2009年。首次发表于2009年1月14日; doi：10.1152/ajpcell.00338.2008。Reissner膜上皮形成了产生和维持耳蜗内淋巴和外淋巴之间的大离子差异的大部分屏障。本文报道了沙鼠内耳Reissner膜通过氨氯地平敏感通道吸收内淋巴液中的Na+，从而维持耳蜗的正常功能。我们使用小鼠Reissner膜1）鉴定参与Na+转运途径的候选基因，2）确定其表达水平是否受合成糖皮质激素地塞米松的调节，3）获得这些基因的生理重要性的功能证据。存在上皮Na+通道（ENaC）的α-、β-和γ-亚基;皮质类固醇受体GR（糖皮质激素受体）和MR（盐皮质激素受体）; GR激动剂调节剂11 β-羟基类固醇脱氢酶（HSD）1型（11 β-HSD 1）; Na+转运控制组分SGK 1、Nedd 4 -2和WNK;以及K+通道和Na+-K+-ATP酶的转录本。未检测到MR激动剂调节剂11 β-HSD 2的表达。地塞米松上调ENaC（类似于6倍和3倍）、KCNK 1（类似于3倍）、11 β-HSD 1（类似于2倍）、SGK 1（类似于2倍）和WNK 4（类似于3倍）的α-和β-亚基的转录物。从Reissner膜的顶端到基底侧的跨上皮电流对阿米洛利（IC 50类似于0.7 μ M）和苯扎米尔（IC 50类似于0.1 μ M）敏感，但对EIPA（IC 50类似于34 μ M）不敏感;阿米洛利阻断的跨上皮电流不会立即被毛喉素/IBMX改变。通过哇巴因、降低的浴Na+浓度（从150至120 mM）和K+通道阻断剂（XE-991、Ba 2+和从pH 7.4至6.5的酸化）降低电流。地塞米松刺激电流和基因表达减少米非司酮，但不螺内酯。这些分子、药理学和功能观察结果与小鼠Reissner膜的Na+吸收一致，其由顶端ENaC和/或其他阿米洛利敏感性通道、基底外侧Na+-K+-ATP酶和K+渗透性通道介导，并受糖皮质激素控制。这些结果提供了一个理解和一个重要的运输功能的Reissner的膜上皮细胞的耳蜗内淋巴的稳态的分子定义。
Kim SH, Kim KX, Raveendran NN, Wu T, Pondugula SR, Marcus DC. Regulation of ENaC-mediated sodium transport by glucocorticoids in Reissner's membrane epithelium. Am J Physiol Cell Physiol 296: C544-C557, 2009. First published January 14, 2009; doi:10.1152/ajpcell.00338.2008.-Reissner's membrane epithelium forms much of the barrier that produces and sustains the large ionic differences between cochlear endolymph and perilymph. We have reported that Reissner's membrane contributes to normal cochlear function by absorbing Na+ from endolymph via amiloride-sensitive channels in gerbil inner ear. We used mouse Reissner's membrane to 1) identify candidate genes involved in the Na+ transport pathway, 2) determine whether their level of expression was regulated by the synthetic glucocorticoid dexamethasone, and 3) obtain functional evidence for the physiological importance of these genes. Transcripts were present for alpha-, beta-, and gamma-subunits of epithelial Na+ channel (ENaC); corticosteroid receptors GR (glucocorticoid receptor) and MR (mineralocorticoid receptor); GR agonist regulator 11 beta-hydroxysteroid dehydrogenase (HSD) type 1 (11 beta-HSD1); Na+ transport control components SGK1, Nedd4-2, and WNKs; and K+ channels and Na+-K+-ATPase. Expression of the MR agonist regulator 11 beta-HSD2 was not detected. Dexamethasone upregulated transcripts for alpha- and beta-subunits of ENaC (similar to 6-and similar to 3-fold), KCNK1 (similar to 3-fold), 11 beta-HSD1 (similar to 2-fold), SGK1 (similar to 2-fold), and WNK4 (similar to 3-fold). Transepithelial currents from the apical to the basolateral side of Reissner's membrane were sensitive to amiloride (IC50 similar to 0.7 mu M) and benzamil (IC50 similar to 0.1 mu M), but not EIPA (IC50 similar to 34 mu M); amiloride-blocked transepithelial current was not immediately changed by forskolin/IBMX. Currents were reduced by ouabain, lowered bath Na+ concentration (from 150 to 120 mM), and K+ channel blockers (XE-991, Ba2+, and acidification from pH 7.4 to 6.5). Dexamethasone-stimulated current and gene expression were reduced by mifepristone, but not spironolactone. These molecular, pharmacological, and functional observations are consistent with Na+ absorption by mouse Reissner's membrane, which is mediated by apical ENaC and/or other amiloride-sensitive channels, basolateral Na+-K+-ATPase, and K+-permeable channels and is under the control of glucocorticoids. These results provide an understanding and a molecular definition of an important transport function of Reissner's membrane epithelium in the homeostasis of cochlear endolymph.