High baseline ROMK activity in the mouse late distal convoluted and early connecting tubule probably contributes to aldosterone-independent K+ secretion
High baseline ROMK activity in the mouse late distal convoluted and early connecting tubule probably contributes to aldosterone-independent K+ secretion
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DOI：
10.1152/ajprenal.00252.2021
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发表时间：
2022-01-01
影响因子：
4.2
通讯作者：
Korbmacher，Christoph
中科院分区：
文献类型：
--
作者：
Nesterov，Viatcheslav;Bertog，Marko;Korbmacher，Christoph
肾外髓K+通道（ROMK）与上皮Na+通道（ENaC）共定位于晚远曲小管（DCT 2）、连接小管（CNT）和皮质集合管（CCD）中。ENaC介导的Na+吸收产生ROMK介导的肾小管K+分泌的电驱动力，这对于维持肾脏K+稳态至关重要。ENaC活性在晚期CNT和早期CCD（CNT/CCD）中是醛固酮依赖性的，但在DCT 2和早期CNT（DCT 2/CNT）中是醛固酮非依赖性的。这表明在低血浆醛固酮的基线条件下，ROMK介导的K+分泌主要发生在DCT 2/CNT中。因此，我们假设基线ROMK活性在DCT 2/CNT中比在CNT/CCD中更高。为了验证这一假设，膜片钳实验中进行的DCT 2/CNT和CNT/CCD显微解剖小鼠维持在一个标准的饮食。在单通道记录从外向补丁，我们检测到典型的ROMK通道活动的DCT 2/CNT和CNT/CCD，并证实，ROMK是主要的K+通道在顶膜。测定阿米洛利敏感性和特硫平敏感性全细胞电流以分别评估ENaC和ROMK活性。正如预期的那样，基线阿米洛利敏感电流在DCT 2/CNT中较高（约370 pA），但在CNT/CCD中较低（约60 pA）。重要的是，DCT 2/CNT中的特硫平敏感电流显著高于CNT/CCD中的特硫平敏感电流（10810对10350 pA）。我们的结论是，高ROMK活性的DCT 2/CNT是关键的醛固酮非依赖性肾K+分泌在基线条件下。低K+饮食显著降低了ENaC，但不降低RCT 2/CNT中的ROMK活性。这表明，修改ENaC活性的DCT 2/CNT中起着关键的调节作用，在调整肾脏的K+排泄饮食K+intake.NEW & NOTEWORTHYROMK介导的肾脏K+分泌是必不可少的维持K+平衡，并需要一个管腔负跨上皮电位严重依赖于ENaC活性。使用显微切割的小鼠远端小管，我们证明了基线顶端ROMK活性在DCT 2/CNT中很高。不依赖于醛固酮的基线ENaC活性在DCT 2/CNT中也很高，并被低K+饮食下调，这突出了DCT 2/CNT以不依赖于醛固酮的方式调节K+分泌的重要作用。
The renal outer medullary K+channel (ROMK) is colocalized with the epithelial Na+channel (ENaC) in the late distal convoluted tubule (DCT2), connecting tubule (CNT), and cortical collecting duct (CCD). ENaC-mediated Na+absorption generates the electrical driving force for ROMK-mediated tubular K+secretion, which is critically important for maintaining renal K+homeostasis. ENaC activity is aldosterone dependent in the late CNT and early CCD (CNT/CCD) but aldosterone independent in the DCT2 and early CNT (DCT2/CNT). This suggests that under baseline conditions with low plasma aldosterone, ROMK-mediated K+secretion mainly occurs in the DCT2/CNT. Therefore, we hypothesized that baseline ROMK activity is higher in the DCT2/CNT than in the CNT/CCD. To test this hypothesis, patch-clamp experiments were performed in the DCT2/CNT and CNT/CCD microdissected from mice maintained on a standard diet. In single-channel recordings from outside-out patches, we detected typical ROMK channel activity in both the DCT2/CNT and CNT/CCD and confirmed that ROMK is the predominant K+channel in the apical membrane. Amiloride-sensitive and tertiapin-sensitive whole-cell currents were determined to assess ENaC and ROMK activity, respectively. As expected, baseline amiloride-sensitive current was high in the DCT2/CNT (∼370 pA) but low in the CNT/CCD (∼60 pA). Importantly, tertiapin-sensitive current was significantly higher in the DCT2/CNT than in the CNT/CCD (∼810 vs. ∼350 pA). We conclude that high ROMK activity in the DCT2/CNT is critical for aldosterone-independent renal K+secretion under baseline conditions. A low-K+diet significantly reduced ENaC but not ROMK activity in the DCT2/CNT. This suggests that modifying ENaC activity in the DCT2/CNT plays a key regulatory role in adjusting renal K+excretion to dietary K+intake.NEW & NOTEWORTHYROMK-mediated renal K+secretion is essential for maintaining K+balance and requires a lumen negative transepithelial potential critically dependent on ENaC activity. Using microdissected distal mouse tubules, we demonstrated that baseline apical ROMK activity is high in the DCT2/CNT. Aldosterone-independent baseline ENaC activity is also high in the DCT2/CNT and downregulated by a low-K+diet, which highlights the important role of the DCT2/CNT in regulating K+secretion in an aldosterone-independent manner.