Regulation of Sodium Transport in the Kidney

描述（由申请人提供）：血压（BP）持续波动，而RBF和GFR由于肾内调节（包括抑制PT重吸收）而没有波动。这改变了NaCI对黄斑致密的递送和肾素的释放，有助于压力性尿钠，从而影响血压设定点。我们之前已经确定，PT Na+重吸收的减少是由转运能力强的Na+/H+交换物（NHE3）从PT微绒毛中缩回介导的，该反应在自发性高血压大鼠（SHR）中被慢性激活，而在肾损伤（RI）高血压中则相反，SNS激活将NHE3移动到微绒毛中，可能通过抵消BP介导的PT Na+运输抑制而导致高血压。这一进展为解决不同急性和慢性高血压模型中控制NHE3再分配的分子机制奠定了基础：NHE3的来源和目的地，NHE3相关蛋白和NHE3活性/转运体在途中是否有变化，以及控制再分配的信号。目的1验证了急性高血压期间NHE3从绒毛缩回涉及根尖表面膜内两步过程的假设(1)从绒毛到微绒毛间隙，(2)然后到微绒毛间包被凹坑，这与NHE3相互作用蛋白、膜结构域性质、Na+/H+交换活性/转运体的变化有关。目的2验证了以下假设：在慢性高血压期间，NHE3在顶域的分布持续变化，可能是代偿性的（如SHR），也可能是促进性的（如慢性RI模型），两者都与NHE3相关蛋白、结构域特性和活性/转运体的明显慢性变化有关。该Aim还验证了当BP归一化时这些变化被逆转/归一化的假设。目的3验证了以下假设：NHE3缩回的第1步依赖于一氧化氮的肾内释放，Ang II的降低对第2步很重要；在由SNS激活驱动的急性RI期间，NHE3从IMC和ICP区域招募到微绒毛，而不是通过调节的胞吐作用。完成这些目标将揭示NHE3（主要的高容量肾Na+转运体）是如何在体内正常范围内的血压急性变化中调节的，以及当遗传或损伤诱导的SNS激活导致血压长期升高时它是如何调节的。

DESCRIPTION (provided by applicant): Blood pressure (BP) continuously fluctuates while RBF and GFR do not due to intra-renal adjustments including inhibition of PT reabsorption. This alters NaCI delivery to the macula densa and renin release and contributes to pressure natriuresis, thus, influences BP set point. We have previously established that the decrease in PT Na+ reabsorption is mediated by a retraction of transport competent Na+/H+ exchangers (NHE3) from the PT microvilli, that the response is chronically activated in the Spontaneously Hypertensive Rat (SHR), and that the converse is evident in Renal Injury (RI) hypertension where SNS activation moves NHE3 into the microvilli, potentially contributing to hypertension by counteracting BP mediated inhibition of PT Na+ transport. This progress sets the groundwork for addressing the molecular mechanisms governing NHE3 redistribution in distinct models of acute and chronic hypertension: the source and destination of NHE3, whether there are changes in NHE3 associated proteins and NHE3 activity/transporter en route, and the signals governing redistribution. Aim 1 tests the hypotheses that NHE3 retraction from the villi during acute hypertension involves a two step process within the apical surface membrane (1) from villi to intermicrovillar cleft, (2) then to intermicrovillar coated pits associated with a change in NHE3 interacting proteins, membrane domain properties, Na+/H+ exchanger activity/transporter, and coincident movement of myosin VI. Aim 2 tests the hypotheses that during chronic hypertension there are persistent shifts in NHE3 distribution within the apical domain that can be either compensatory, as in the SHR, or contributory, as in the chronic RI model both associated with distinct chronic changes in NHE3 associated proteins, domain properties and activity/transporter. This Aim also tests the hypothesis that these changes are reversed/normalized when BP is normalized. Aim 3 tests the hypotheses that Step 1 of NHE3 retraction is dependent on the intrarenal release of nitric oxide that a decrease in Ang II is important for Step 2, and that during acute RI driven by SNS activation NHE3 is recruited from the IMC and ICP regions to the microvilli, rather than by regulated exocytosis. Accomplishing these Aims will reveal how NHE3, the major high capacity renal Na+ transporter, is regulated in vivo by an acute change in blood pressure in the normal range and how it is regulated when BP is chronically elevated by genetics or injury induced SNS activation.