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，因为 低钾血症或高钾血症可能导致危及生命的后果，如心律失常。一个 该领域的最新发展已经牢固地确立了噻嗪敏感的钠-氯共转运体的作用 (NCC)在调节K+动态平衡中的作用，因为NCC与上皮细胞Na+之间的协调作用 通道(ENaC)和ROMK是最大限度地增加高饮食时肾脏K+排泄(EK)所必需的 K+摄入量(HK)，并有效防止低K+摄入量(LK)时K+的浪费。基底外侧 远曲小管(DCT)中的KIR4.1和Kir5.1通道在控制NCC中起着重要作用 表情和活动。我们以前的研究表明，HK诱导了Kir4.1/Kir5.1的抑制 是HK抑制NCC的关键步骤。相反，LK诱导的Kir4.1/Kir5.1刺激 DCT的激活是LK刺激NCC的关键步骤。这是一种机制 DCT中基侧Kir4.1/Kir5.1对NCC活性的调节依赖于氯离子敏感的非赖氨酸激酶 (WNK)。Kir4.1和Kir5.1在调节肾脏K+排泄中的作用已在 小鼠模型：Kir4.1基因缺失抑制NCC活性并导致肾脏K+消耗，而Kir4.1基因缺失 Kir5.1基因缺失增加了NCC活性，降低了肾K+的排泄能力。因此， DCT中的KIR4.1和KIR5.1是钾传感器机制的两个重要成员。虽然 Kir4.1/Kir5.1在调节NCC和肾脏K+排泄方面的作用是确定的，调节 膳食K+摄入量调节Kir4.1和Kir5.1的机制尚不完全清楚。我们现在 建议研究雷帕霉素(MTOR)复合体1(MTORC1)和mTOR机制靶点的作用 复合体2(MTORC2)介导膳食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mTORC1是至关重要的 参与介导LK摄入对DCT和NCC Kir4.1/Kir5.1的刺激；2) MTORC2激活抑制PKC在HK诱导的Kir4.1/Kir5.1的表达 对NCC的抑制。该提案有三个具体目标：1)检验mTORC1调控的假设 DCT和NCC在控制条件(正常K+)下的KIR4.1/Kir5.1，并在决定 基础肾K+排泄；2)检验IGF1-mTORC1激活在肾功能衰竭中起关键作用的假设 介导LK刺激DCT和NCC中Kir4.1/Kir5.1及抑制肾K+的作用 3)验证mTORC2激活介导HK抑制Kir4.1/Kir5.1的假设 通过DCT中的PKC和NCC，从而增强ENaC依赖的肾脏EK。我们的重要意义在于 目的是探讨mTORC1/mTORC2通路在LK或HK对心肌梗死的影响中的新作用。 KIR4.1/Kir5.1、NCC、ENaC和ROMK在DCT和连接小管中。

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.