Role of BK-alpha/beta 4 in renal secretion

描述(由申请人提供)：据估计，21%的住院患者会出现高钾血症。然而，在低钠摄入量时消除大量钾的机制尚不清楚。通常认为是通过远端肾单位主细胞中钾与钠的直接交换而发生的，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解偶联。如果不了解调节这一过程的钾通道，就不能为血浆[K]急剧升高的患者开发更好的治疗方法。我们的长期目标是了解特定的肾脏离子通道对K的清除作用。我们的重点是肾远端大的钙激活的钾通道(BK)，它包含辅助的BK-b4(BK-a/b4)，在碱性分泌(IC-b)和酸性分泌(IC-a)的嵌入细胞中。这里的目标是研究bk-a/b4在高K条件下分泌K的作用，这是我们迈向长期目标的关键一步。我们报道，当BK-B4基因敲除小鼠(B4-KO)处于高K饮食7-10天(K适应；KA)时，它们表现出与野生型相比血浆[K]升高和消除K的能力降低40%。此外，与高K饮食相关的高流量会激活bk-a/b4，导致K的释放和细胞尺寸的减小。因此，bk-a/b4在肾脏如何处理高钾饮食中起着重要作用；然而，bk-a/b4在这一能力中发挥作用的机制尚不清楚。中心假说是，KA小鼠体内升高的醛固酮通过一种钠非依赖性的机制促进钾的分泌，这种机制利用BK-a/b4在IC-b中分泌K，并通过Bk-a/b4在外髓集合管的IC-a中循环K。这一假说将通过追求三个特定的目标来验证：1.确定醛固酮或高K是否促进KA小鼠BK-a/B4介导的K分泌。2.确定bk-a/b4在钠非依赖性钾分泌中的作用。3.确定bk-a/b4和KCC4在有机钾肥循环和增流中的作用。在这些研究中，我们将使用包括肾清除测量、膜片钳和免疫组织化学分析等方法对WT和b4-KO小鼠进行研究。这种方法是创新的，因为我们测试了一种新的钠非依赖性钾分泌模型，同时分离了每种可能的机制。这项拟议的研究具有重要意义，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取过程中消除大量钾的机制。这样的认识可能有助于防止每年发生的大量死亡，因为使用醛固酮受体阻滞剂治疗心力衰竭受试者会导致高钾血症引起的室性心律失常。

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.