Role of BK-alpha/beta 4 in renal secretion

描述（由申请人提供）：高钾血症估计发生在21%的住院患者中。然而，在低钠摄入期间消除大量钾的机制尚不清楚。传统上，它被认为是在远端肾元主细胞中通过钾与钠的直接交换发生的，但当血浆[K]高而钠摄入量少时，钾的分泌必须与钠的重吸收分离。如果不了解介导这一过程的K通道，就无法开发出更好的治疗急性血浆升高患者的方法[K]。我们的长期目标是了解特异性肾离子通道在消除钾中的作用。我们的重点是远端肾元中含有辅助BK-b4 （BK-a/b4）的钙激活的钾通道（BK），这些通道位于分泌碱（IC-b）和分泌酸（IC-a）的插层细胞中。这里的目标是研究BK-a/b4在高K条件下分泌K的作用，这是我们实现长期目标的关键一步。我们报道，当BK-b4敲除小鼠（b4-KO）被置于高钾饮食中7-10天（K适应；KA）时，与野生型相比，它们表现出血浆[K]增加，消除K的能力降低40%。此外，与高钾饮食相关的高流量激活BK-a/b4，导致K的释放和细胞大小的减小。因此，BK-a/b4在肾脏如何处理高钾饮食中起主要作用；然而，BK-a/b4在这种能力中发挥作用的机制尚不清楚。核心假设是，KA小鼠醛固酮升高通过一种不依赖na的机制促进K的分泌，该机制利用了外髓集管（OMCD）中BK-a/b4分泌K和BK-a/b4在IC-a中的K循环。这一假设将通过追求三个具体目标来检验：1。确定醛固酮或高血浆K是否能增强KA小鼠BK-a/b4介导的K分泌。2. 确定BK-a/b4在na非依赖性K分泌中的作用。3. 确定BK-a/b4和KCC4在OMCD K循环和流量增强中的作用。在这些研究中，我们将采用包括肾清除率测量、贴片夹持和WT和b4-KO小鼠的免疫组织化学分析等方法。该方法是创新的，因为我们测试了一种新的na独立的K分泌模型，同时分离了每种潜在的机制。拟议的研究意义重大，因为它有望回答一些长期存在的问题，即在非常少量的钠摄入中消除大量钾的机制。这样的认识可能有助于防止每年因使用醛固酮受体阻滞剂治疗心力衰竭而导致高钾血症诱发的室性心律失常而导致的大量死亡。

DESCRIPTION (provided by applicant): Hyperkalemia is estimated to occur in 21% of hospitalized patients. However, the mechanism for eliminating high quantities of K during low Na intake is not known. Conventionally, it was thought to occur by direct exchange of K for Na in principal cells of the distal nephron, but when plasma [K] is high with little Na intake, K secretion must be uncoupled from Na reabsorption. Without an understanding of the K channels that mediate this process, better therapies for victims with acutely elevated plasma [K] cannot be developed. Our long-term goal is to understand the role of specific renal ion channels to eliminate K. Our focus is the large, Ca-activated K channels (BK) in the distal nephron that contain the accessory BK-b4 (BK-a/b4) in base-secreting (IC-b) and acid-secreting (IC-a) intercalated cells. The objective here, which is a critical step toward our long-goal, is to examine the role of BK-a/b4 in secreting K under high K conditions. We reported that when BK-b4 knock-out mice (b4-KO) are placed on a high K diet for 7-10 days (K adapted; KA), they exhibit increased plasma [K] and a 40% reduction in the capacity to eliminate K compare to wild type. Furthermore, high flow associated with a high K diet activates BK-a/b4, causing a release of K and cell size reduction. Thus, BK-a/b4 play a major role in how the kidney handles a high K diet; however, the mechanism by which BK-a/b4 function in this capacity is not well understood. The central hypothesis is that the elevated aldosterone of KA mice enhances K secretion by a Na-independent mechanism that utilizes K secretion by BK-a/b4 in the IC-b and K recycling by BK-a/b4 in the IC-a of the outer medullary collecting duct (OMCD). This hypothesis will be tested by pursuing three specific aims: 1. Determine whether aldosterone or high plasma K enhances BK-a/b4-mediated K secretion in KA mice. 2. Determine the role of BK-a/b4 in Na-independent K secretion. 3. Determine the roles of BK-a/b4 and KCC4 in the OMCD K recycling and flow enhancement. For these studies, we will employ methods including renal clearance measurements, patch clamping and immunohistochemical analysis of WT and b4-KO mice. The approach is innovative because we test a new model of Na-independent K secretion while isolating each potential mechanism. The proposed research is significant because it is expected to answer some long- standing questions regarding the mechanism for eliminating high quantities of K during very small amounts of Na intake. Such understanding may help prevent the large number of deaths occurring each year from treating heart failure subjects with aldosterone receptor blockers that lead to hyperkalemia-induced ventricular arrhythmias.