Membrane Processes Mediating K Secretion

肾脏通过在尿液中排泄大约相同的钾来维持体内钾（K）的平衡 在饮食中摄入的钾量。在大多数情况下，它通过分泌K进入尿液， 远端肾单位和集合管。该机制至少部分涉及K的运动， 细胞通过顶膜上的离子通道进入尿液。连接小管（CNT）， 连接远曲小管和皮质集合管（CCD）的部分是K 分泌物我们已经确定了两个钾通道在顶端膜的大鼠CNT：低电导 (SK，ROMK）通道和高电导（BK，maxi-K）通道。在这里，我们建议审查 在我们最初的发现中，SK通道的滥用并不是通过调节CNT中的这些通道来实现的。 增加CNT，因为它是在CCD时，动物s。我们将测试是否设置点为 监管转移在CNT。或者，我们将研究是否差异与 表达的ROMK同种型。我们还将研究肽对SK通道的调节 激素包括ADH和胰高血糖素。BK通道主要存在于闰细胞中 的CNT。我们将询问这些通道在静止条件下的低开放概率是否可以 增加到足以促进钾的分泌。刺激将包括激素刺激， 增加了膜上的剪切应力。我们还将询问，插入细胞对钾的摄取是否 通过Na/K-ATP酶足以支持显著的K分泌。最后，我们将量化K 分泌在远端肾单位在各种条件下，并询问它是否可以占的， 测量细胞的电生理特性。第二套目标将侧重于以下进程： 通过SK/ROMK通道渗透。我们将检验这样一个假设，即K运动涉及到 通过“细胞质孔”运输，细胞质孔是突出到细胞质中的通道蛋白的一部分 并且是内向整流器K沟道系列所独有的。我们将进一步研究饱和的机制 使用定点诱变的方法来测量通道阻抗。这些研究应阐明 肾脏如何在严格控制下维持血浆K的过程。失去这种控制，例如， 遗传性疾病，如巴特综合征或吉特尔曼综合征，具有严重的后果，包括改变 细胞兴奋性心律失常和肌肉无力

The kidney maintains the balance of potassium (K) in the body by excreting in the urine about the same amount of K that is ingested in the diet. Under most conditions it does this by secreting K into the urine in the distal nephron and collecting duct. The mechanism involves, at least in part, the movement of K from the cells into the urine through ion channels in the apical membrane. The connecting tubule (CNT), a segment joining the distal convoluted tubule and the cortical collecting duct (CCD)is an important site for K secretion. We have indentified two K channels in the apical membrane of the rat CNT:a low conductance (SK, ROMK) channel and a high conductance (BK, maxi-K) channel. Here we propose to examine the regulation of these channels in the CNT.In our initial findings the abudnance of SK channels was not increased in the CNT as it was in the CCD when the animal s. We will test whether the set-point for regulation is shifted in the CNT.Alternatively, we will examine whether the difference is related to the ROMK isoform which is expressed. We will also examine the regulation of the SK channels by peptide hormones including ADH and glucagon. The BK channels were observed primarily in the intercalated cells of the CNT. We will ask whether the low open probability of these channels under resting conditions can be increased sufficiently for them to contribute to K secretion. Stimuli will include hormone stimulation and increased shear stress on the membrane. We will also ask whether K uptake by the intercalated cells through the Na/K-ATPase is adequate to support a significant K secretion. Finally, we will quantify K secretion in the distal nephron under various conditions and ask whether it can be accounted for by the measured electrophysiological properties of the cells. A second set of aims will focus on the process of permeation through SK/ROMK channels. We will test the hypothesis that this K movement involves transport through the "cytoplasmic pore", a part of the channel protein which protrudes into the cytoplasm and is unique to the inward-rectifier K channel family. We will further examine the mechanism of saturation of channel condutance using a site-directed mutagenesis approach. These studies should elucidate the processes of how the kidney maintains plasma K under tight control. Loss of this control, for example in genetic diseases such as Bartter's or Gitelman's syndromes, has serious consequences including altered cell excitability, cardiac arrhythmias and muscle weakness.