Regulation of renal Na handling in the collecting duct by local purinergic tone

描述（由申请人提供）：醛固酮敏感性远端肾单位主细胞中上皮Na+通道（ENaC）的活性对肾盐和水处理至关重要，因此对血压调节至关重要。事实上，ENaC功能的获得和丧失导致血压的显著升高和降低。ENaC通过肾素-血管紧张素-醛固酮系统（RAAS）的负反馈调节被充分描述，其中血压的变化最终影响肾脏中的ENaC活性。新出现的证据表明，ENaC也受到局部因素介导的肾脏固有信号传导的反馈控制。然而，与RAAS的外在调节相比，对内在控制的了解较少。嘌呤能信号传导因子是自分泌/旁分泌因子的主要候选者，其对远端肾单位Na+转运很重要。我们的总体想法是，远端肾单位盐和水的处理受到内在系统的影响，以减少近端事件的远端补偿，使排泄能够适当地匹配全身条件。这种内在调节的丧失预计会导致或加剧不适当的肾脏Na+潴留，从而导致高血压。令人惊讶的是，经工程改造以缺乏嘌呤能P2 Y2受体或连接蛋白30半通道（其可能部分地负责远端肾单位中的ATP释放）的小鼠具有与易化的肾Na+潴留相关的高血压。考虑到我们强有力的初步结果，我们测试了我们的中心假设，即通过管腔P2 Y2受体响应远端肾单位中的局部ATP信号传导的ENaC活性的生理性下调通过解决四个具体目标来调节Na+重吸收：第一章确定生理浓度的ATP是否影响哺乳动物远端肾单位中的ENaC活性，并确定细胞信号传导途径和机制，行动; 2）通过受损的旁分泌/自分泌ATP信号传导确定ENaC的功能失调调节的后果; 3）确定连接蛋白30在ENaC的ATP调节中的作用;和4）量化全身盐负荷和通过嘌呤能紧张调节远端肾单位中的ENaC活性之间的关系。我们调查嘌呤调节ENaC使用一个全面的战略相结合的直接测量通道活性与电生理学的分子遗传学方法，明确建立的作用P2 Y2受体和探针Cx 30作为自分泌ATP释放的管道。使用在其正常细胞环境中含有天然ENaC的生理相关组织（新鲜分离的鼠集合管）。此外，该提案的范围是通过动物集合管中的嘌呤能张力和ATP释放（通过Cx 30）对ENaC进行全面的探索调节，以达到作用的分子机制。

DESCRIPTION (provided by applicant): The activity of the epithelial Na+ channel (ENaC) in principal cells of the aldosterone-sensitive distal nephron is central to renal salt and water handling, and thus, regulation of blood pressure. Indeed, gain and loss of ENaC function causes marked increases and decreases in blood pressure. Negative-feedback regulation of ENaC by the renin-angiotensin-aldosterone system (RAAS) is well described where changes in blood pressure ultimately affect ENaC activity in the kidney. Emerging evidence suggests that ENaC is also under feedback control by signaling intrinsic to the kidney mediated by local factors. However, compared to extrinsic regulation by RAAS, less is known about intrinsic control. Purinergic signaling factors are leading candidates as autocrine/paracrine factors important to distal nephron Na+ transport. Our overarching idea is that distal nephron salt and water handling is influenced by intrinsic systems to lessen distal compensation of proximal events enabling excretion to appropriately match systemic conditions. Loss of such intrinsic regulation is expected to cause or exacerbate improper renal Na+ retention and thus, hypertension. It is striking that mice engineered to lack purinergic P2Y2 receptors or connexin 30 hemi-channels, which likely are responsible, in part, for ATP release in the distal nephron, have hypertension associated with facilitated renal Na+ retention. In consideration of our strong preliminary results, we test our central hypothesis that physiological down- regulation of ENaC activity in response to local ATP signaling in the distal nephron through luminal P2Y2 receptors tempers Na+ reabsorption by addressing four specific aims: 1) determine whether physiological concentrations of ATP affect ENaC activity in the mammalian distal nephron and determine the cellular signaling pathway and mechanism of action; 2) determine the consequence of dysfunctional regulation of ENaC by compromised paracrine/autocrine ATP signaling; 3) define the role of connexin 30 in ATP regulation of ENaC; and 4) quantify the relation between systemic salt-loading and regulation of ENaC activity in the distal nephron by purinergic tone. We investigate purinergic regulation of ENaC using a comprehensive strategy combining direct measurements of channel activity with electrophysiology with a molecular genetics approach that unequivocally establishes the role of the P2Y2 receptor and probes Cx30 as a conduit for autocrine ATP release. Physiologically relevant tissue (freshly isolated murine collecting duct) containing native ENaC in its normal cellular environment is used. Moreover, the scope of this proposal is comprehensive probing regulation of ENaC by purinergic tone and ATP release via Cx30 in the collecting duct from the animal to molecular mechanism of action.