Regulation of Kir4.1/Kir5.1 and renal potassium excretion

维持K+稳态对心脏、骨骼肌和神经元的功能至关重要， 低钾血症或高钾血症可导致危及生命后果，例如心律失常。一 该领域的最新进展已经确定了噻嗪敏感性钠-氯共转运蛋白的作用 (NCC)由于NCC、上皮细胞Na+、Na+和Na+之间的协同作用， 在高饮食期间，ENaC和ROMK对于最大限度地增强肾脏K+排泄（EK）是必不可少的。 K+摄入量（HK）和有效防止低膳食K+摄入量（LK）时K+浪费。基底外侧 远曲小管（DCT）的Kir4.1和Kir5.1通道在NCC的调控中起重要作用 表达和活动。我们以前的研究表明HK可抑制Kir4.1/Kir5.1 是HK诱导的NCC抑制的重要步骤。相反，LK诱导的Kir4.1/Kir5.1刺激 DCT的重建是LK刺激NCC的重要步骤。的机制 DCT中的基底外侧Kir4.1/Kir5.1依赖于Cl-敏感的无赖氨酸激酶调节NCC活性 （WNK）。Kir4.1和Kir5.1在肾脏K+排泄调节中的作用已在以下研究中得到证实： 小鼠模型：Kir4.1的缺失抑制NCC活性并导致肾K+消耗，而Kir4.1的缺失抑制NCC活性并导致肾K+消耗。 在HK摄入期间，Kir5.1的缺失增加NCC活性并降低肾脏K+排泄能力。因此，在本发明中， DCT中的Kir4.1和Kir5.1是“钾敏感”机制的两个重要成员。虽然 Kir4.1/Kir5.1在调节NCC和肾脏K+排泄中的作用已被充分确定， 膳食K+摄入调节Kir4.1和Kir5.1的机制尚未完全清楚。我们现在 我建议研究雷帕霉素（mTOR）复合物1（mTORc 1）和mTOR的机制靶点的作用， 复合物2（mTORc 2）介导了膳食K+摄入对DCT Kir4.1/Kir5.1的影响。我们 假设1）部分通过胰岛素样生长因子1（IGF-1）激活mTORc 1， 参与介导LK摄入诱导的DCT和NCC的Kir4.1/Kir5.1刺激; 2） mTORc 2的激活通过PKC抑制HK过程中的Kir4.1/Kir5.1，并参与HK摄入诱导的 抑制NCC。该提案有三个具体目的：1）测试mTORc 1调节的假设 Kir4.1/Kir5.1，并在确定正常K+条件下DCT和NCC的 基线肾K+排泄; 2）为了验证IGF 1-mTORc 1激活在肾K+排泄中起关键作用的假设， 介导LC诱导的DCT和NCC中Kir4.1/Kir5.1的刺激和抑制肾K+ 3）检验mTORc 2的激活介导HK诱导的Kir4.1/Kir5.1抑制的假设 通过DCT中的PKC和NCC，从而增强ENaC依赖性肾EK。我们的重要性 我们的建议是探索mTORc 1/mTORc 2通路在介导LK或HK对 Kir4.1/Kir5.1、NCC、ENaC和ROMK在DCT和连接小管中的表达。

Maintaining K+ homeostasis is essential for the function of heart, skeletal muscles and neurons because hypokalemia or hyperkalemia could cause life-threatening consequence such as cardiac arrhythmia. A recent development in the field has firmly established the role of thiazide-sensitive Na-Cl cotransporter (NCC) in the regulation of K+ homeostasis because the coordinated action among NCC, epithelial Na+ channel (ENaC) and ROMK is essential for maximally enhancing renal K+ excretion (EK) during high dietary K+ intake (HK) and for effectively preventing K+ wasting during low dietary K+ intake (LK). The basolateral Kir4.1 and Kir5.1 channels in the distal convoluted tubule (DCT) play an important role in controlling NCC expression and activity. Our previous studies have demonstrated that HK induced inhibition of Kir4.1/Kir5.1 is an essential step for HK-induced inhibition of NCC. Conversely, LK-induced stimulation of Kir4.1/Kir5.1 of the DCT is an essential step for LK-induced stimulation of NCC. The mechanism by which the basolateral Kir4.1/Kir5.1 in the DCT regulates NCC activity depends on Cl--sensitive with-no-lysine kinase (WNK). The role of Kir4.1 and Kir5.1 in the regulation of renal K+ excretion has been demonstrated in the mouse models: The deletion of Kir4.1 inhibits NCC activity and causes renal K+ wasting, whereas the deletion of Kir5.1 increases NCC activity and reduces renal K+ excretion ability during HK intake. Thus, Kir4.1 and Kir5.1 in the DCT serve as two important members of “potassium-sensor” mechanism. Although the role of Kir4.1/Kir5.1 in regulating NCC and renal K+ excretion is well established, the regulatory mechanism by which dietary K+ intake modulates Kir4.1 and Kir5.1 is not completely understood. We now propose to examine the role of mechanistic target of rapamycin (mTOR) complex 1 (mTORc1) and mTOR complex 2 (mTORc2) in mediating the effect of dietary K+ intake on Kir4.1/Kir5.1 of the DCT. We hypothesize 1) Activation of mTORc1, partially via insulin-like-growth factor 1 (IGF-1), is critically involved in mediating LK-intake-induced stimulation of Kir4.1/Kir5.1 of the DCT and NCC; 2) Activation of mTORc2 inhibits Kir4.1/Kir5.1 by PKC during HK and is involved in HK-intake-induced inhibition of NCC. The proposal has three specific Aims: 1)To test the hypothesis that mTORc1 regulates Kir4.1/Kir5.1 of DCT and NCC under control conditions (normal K+) and plays a role in determining the baseline renal K+ excretion; 2) To test the hypothesis that activation of IGF1-mTORc1 plays a key role in mediating LK-induced stimulation of Kir4.1/Kir5.1 in the DCT and NCC and in suppressing renal K+ excretion; 3) Test the hypothesis that Activation of mTORc2 mediates HK-induced inhibition of Kir4.1/Kir5.1 via PKC and NCC in the DCT thereby enhancing ENaC-dependent renal EK. The significance of our proposal is to explore the novel role of mTORc1/mTORc2 pathways in mediating effects of LK or HK on Kir4.1/Kir5.1, NCC, ENaC and ROMK in the DCT and connecting tubule.