REGULATION OF RENAL K+ EXCRETION BY GUT FACTOR

描述(由申请人提供)：K+稳态对于正常的心血管和神经肌肉功能至关重要，K+稳态紊乱(例如，高钾血症)可导致危及生命的心血管事件。我们的长期目标是全面了解K+动态平衡机制。细胞外K+稳态是通过肾脏和肾外机制维持的。肾脏有很强的调节K+排泄以匹配K+摄入的能力。我们最近通过不同的途径(即颈静脉、肝门静脉和胃)向大鼠体内注入K+，研究了K+摄入量的感觉。结果表明，当K+与食物一起进入胃时，血浆K+清除量显著增加，提示在饮食K+摄入过程中存在肠道因素，增加了血浆K+清除量。此外，肾K+排泄效率明显增加，提示存在胃-肾K+轴。这些具有挑衅性的发现是有限的，因为不同的K+输注组的血浆K+水平不同，因此，在不同的血浆K+水平下评估了肾脏的K+排泄效率。此外，我们没有评估 肾外细胞K+摄取。我们开发了K+钳技术来定量测定肾脏的K+ 大鼠在不同条件下相匹配的K+水平的排泄和细胞K+摄取。我们建议结合K+钳技术和K+输注实验来跟进我们的新发现：我们将检验存在肠道因素的假设，并确定其潜在的机制。目的1.验证一种假设，即在饮食K+摄入过程中，存在促进肾脏和肾外K+转运的肠道因素。使用K+钳技术，我们将试图确定当K+与食物一起进入胃时，肠道因子被激活，并且它不仅刺激肾K+排泄，而且还刺激肾外细胞K+摄取。我们还将测试其对肾脏K+排泄的影响是否由肾脏中ROMK的激活所介导。目的2.验证肠道因子只有在膳食营养存在的情况下才被激活的假设，包括体液因子的分泌，而不是神经调节。我们将测试肠道因子是否通过同时向肠道内注入K+和葡萄糖来激活，以及其对肾脏K+排泄的影响是否由体液因子(已知或未知)或向肾脏的传出神经通路介导。该项目将潜在地建立一个重要的，以前未知的因素，即肠道因素，在维持K+稳态方面的存在，可以通过随后的R01拨款在细胞或分子水平上进行鉴定和研究。公共卫生相关性这个项目可能会确定存在一个重要的、以前未知的因素(即肠道因素)，该因素在饮食中K+摄入量期间被激活以维持K+稳态。如果随后发现一种新的肠道因子，将极大地提高我们对K+稳态机制的理解。此外，有一种耐人寻味的可能性，即这种因素可能介导了增加饮食K+摄入量对高血压、中风和/或心血管疾病的一些有益影响。

DESCRIPTION (provided by applicant): K+ homeostasis is critical for normal cardiovascular and neuromuscular function, and disturbances in K+ homeostasis (e.g., hyperkalemia) can lead to life-threatening cardiovascular events. Our long-term objective is to fully understand K+ homeostatic mechanisms. Extracellular K+ homeostasis is maintained by renal and extrarenal mechanisms. The kidneys have a remarkable capacity to regulate K+ excretion to match K+ intake. We recently studied the sensing of K+ intake by infusing K+ into rats via various routes (i.e., jugular vein, hepatic portal vein, and stomach). The results demonstrated that, when K+ enters the stomach together with a meal, there was a marked increase in plasma K+ clearance, suggesting the existence of a gut factor that increases plasma K+ clearance during dietary K+ intake. Additionally, there was an apparent increase in renal efficiency of K+ excretion, suggesting that there is a gastric-renal K+ axis. These provocative findings are limited in that plasma K+ level was not the same in the different K+ infusion groups, and, thus, renal efficiency of K+ excretion was assessed at different plasma K+ levels. In addition, we did not assess extrarenal cellular K+ uptake. We developed the K+ clamp technique for quantification of both renal K+ excretion and cellular K+ uptake at matched K+ levels under various conditions in rats. We propose to combine the K+ clamp technique with the K+ infusion experiments to follow up on our novel findings: we will test the hypothesis that there is a gut factor and identify the underlying mechanisms. Aim 1. Test the hypothesis that there is a gut factor that enhances both renal and extrarenal K+ handling during dietary K+ intake. Using the K+ clamp technique, we will attempt to establish that a gut factor is activated when K+ enters the stomach together with a meal and that it stimulates not only renal K+ excretion but also extrarenal cellular K+ uptake. We will also test whether the effect on renal K+ excretion is mediated by ROMK activation in the kidney. Aim 2. Test the hypothesis that the gut factor is activated only in the presence of meal nutrients, involving secretion of humoral factors, but not neural regulation. We will test whether the gut factor is activated by concurrent infusion of K+ and glucose into the gut and whether its effect on renal K+ excretion is mediated by a humoral factor (known or unknown) or an efferent neural pathway to the kidneys. This project will potentially establish the existence of an important, previously unknown factor, i.e., gut factor, in the maintenance of K+ homeostasis, which could be identified and studied at cellular or molecular levels by a subsequent R01 grant. PUBLIC HEALTH RELEVANCE This project will potentially establish the existence of an important, previously unknown factor (i.e., gut factor) that is activated for K+ homeostasis during dietary K+ intake. If a novel gut factor is subsequently identified, it would greatly enhance our understanding of K+ homeostatic mechanisms. In addition, there is an intriguing possibility that such a factor mediates some of the beneficial effects of increased dietary K+ intake on hypertension, stroke, and/or cardiovascular disease.