Physiologic role of BK channel in distal nephron

描述（由申请人提供）：远端肾元（包括连接小管（CNT）和皮质收集管（CCD））的血流刺激K分泌是由位于顶膜的Ca2+和拉伸激活的BK通道介导的；BK通道也在肾脏对膳食钾摄入量的适应中起关键作用。在酸碱运输嵌入细胞中，BK通道的密度大于吸收Na的CNT/主细胞。然而，功能测量表明，插入细胞可能没有一种机制来负载含有钾的细胞，以维持高的钾分泌到尿液中。本应用的目的是确定插入细胞和/或主细胞中的BK通道是否介导血流刺激的净K分泌，从而调节全身K（和Na）稳态。为此，我们提出了三个特定目的（Specific Aims, SAs）：(1)使用选择性BK通道阻滞剂，确认从WT分离的微灌注cd和我们将在ssa2和ssa3中使用floxed slo1生成的小鼠品系中流动刺激的净K分泌是由BK通道介导的；(2)通过构建靶向缺失远端肾元插入细胞中BK通道1亚基的小鼠模型，确定嵌入细胞中BK通道1亚基在体内调节远端肾元K分泌中的作用；(3)通过构建仅在远端肾元内主要细胞中靶向缺失BK通道1亚基的小鼠模型，确定主细胞中BK通道1亚基在体内调节远端肾元K分泌中的作用。在一定程度上，远端钾分泌的大小决定了钠的吸收，而BK通道亚基全缺失的动物存在血压改变，远端肾元中细胞特异性缺失BK通道对钠和钾的清除和血压的影响（遥测）也将被评估。这些研究的结果将确定BK通道在调节肾K（和Na）排泄和维持正常血压中的重要性，并有望揭示高血压和K排泄障碍的发展和/或维持的机制。

DESCRIPTION (provided by applicant): Flow-stimulated K secretion in the distal nephron, including the connecting tubule (CNT) and cortical collecting duct (CCD), is mediated by a Ca2+ and stretch-activated BK channel located in the apical membrane; the BK channel is also critically involved in the renal adaptation to dietary K intake. The density of BK channels in acid-base transporting intercalated cells exceeds that in Na absorbing CNT/principal cells. However, functional measurements suggest that intercalated cells may not have a mechanism to load cells with K to sustain high rates of K secretion into the urinary fluid. The goal of this application is to determine whether BK channels in intercalated and/or principal cells mediate flow-stimulated net K secretion and thereby regulate total body K (and Na) homeostasis. To this end, we propose three Specific Aims (SAs): (1) to confirm, using a selective BK channel blocker, that flow-stimulated net K secretion in microperfused CDs isolated from WT and a mouse strain we will generate with floxed slo1, proposed to be used in SAs 2 and 3, is mediated by the BK channel; (2) to define the role of the 1 subunit of the BK channel in intercalated cells in the in vivo regulation of K secretion in the distal nephron by generating a mouse model with targeted deletion of the 1 subunit of the BK channel solely in intercalated cells within the distal nephron; and (3) to define the role of the 1 subunit of the BK channel in principal cells in the in vivo regulation of K secretion in the distal nephron by generating a mouse model with targeted deletion of the 1 subunit of the BK channel solely in principal cells within the distal nephron. To the extent that the magnitude of distal K secretion determines, in part, Na absorption, and animals with global deletion of BK channel subunits present with alterations in blood pressure, the impact of cell-specific deletion of the BK channel in the distal nephron on Na and K clearances and blood pressure (telemetry) will also be evaluated. The results of proposed studies will define the importance of BK channels in the regulation of renal K (and Na) excretion and maintenance of normal blood pressure, and promises to uncover mechanisms involved in the development and/or maintenance of hypertension and disorders of K excretion. PUBLIC HEALTH RELEVANCE: The proposed studies are designed to determine the physiologic role of BK potassium channels in the distal nephron of the kidney. The studies will define the importance of these channels in the regulation of kidney sodium and potassium excretion and maintenance of normal blood pressure. This work has the potential to uncover mechanisms involved in the development and/or maintenance of hypertension and disorders of potassium excretion.