ROLE OF SENSING OF K+ INTAKE IN K+ HOMEOSTASIS

描述（由申请人提供）：细胞外（ECF） K+稳态对正常的心血管和神经肌肉功能至关重要，并通过肾脏和外肾机制维持。我们最近开发了K钳技术，可以定量体内肾脏K+排泄和肾外细胞K+摄取。使用这种技术，我们证明了肾K+排泄和肾外细胞K+摄取在K+剥夺期间被迅速而深刻地抑制。ecfk +保存的这些变化传统上被解释为由于ecfk +水平降低和/或随之而来的醛固酮分泌减少。然而，我们发现，当K+摄入量减少到对照的1/3时，在血浆[K +]或[醛固酮]没有变化的情况下，这种触发ECF K+保护的情况可能发生在大鼠身上。本项目的目的是验证这样一种假设，即门静脉中的K+传感器可以感知K+的摄入，肾脏的K+排泄和肾外细胞的K+摄取都受该信号的调节。为了实现这一目标，我们将与我们机构的Casey Donovan博士合作，采用类似于用于证明大鼠门静脉葡萄糖传感器存在的策略，即“局部灌溉”和门静脉去神经控制技术。我们的初步数据显示，仅一晚（12小时）将K+摄入量减少到正常水平的1/3，就足以引发肾脏K+的显著保存。在拟议的研究中，我们将使用这种隔夜低K+喂养模型来解决以下具体目标。

DESCRIPTION (provided by applicant): Extracellular (ECF) K+ homeostasis is critical for normal cardiovascular and neuromuscular functions and is maintained by renal and extrarenal mechanisms. We recently developed the K clamp technique, which can quantify both renal K+ excretion and extrarenal cellular K+ uptake in vivo. Using this technique, we demonstrated that both renal K+ excretion and extrarenal cellular K+ uptake are rapidly and profoundly suppressed during K+ deprivation. These changes for ECF K+ conservation have been traditionally explained to arise from decreased ECF K+ levels and/or consequent decrease in aldosterone secretion. However, we found that this triggering of ECF K+ conservation can occur in rats in the absence of changes in plasma [K +] or [aldosterone] when K+ intake is reduced to 1/3 of control. The objective of this project is to test the hypothesis that K+ intake is sensed by K+ sensors in the portal vein, and both renal K+ excretion and extrarenal cellular K+ uptake are regulated by this signal. To achieve this goal, we will collaborate with Dr. Casey Donovan at our institution and employ strategies similar to those used to demonstrate the presence of portal vein glucose sensors in rats, i.e., "local irrigation" and portal denervation techniques. Our preliminary data showed that reducing K+ intake to 1/3 of normal for only one night (12 h) was sufficient to trigger marked renal K+ conservation. In the proposed studies we will use this overnight low K+ feeding model to address the following specific aims. Aim 1. Test for the existence of portal (or splanchnic) sensing of Kv intake and its regulation of renal and extrarenal K+ handling. We will test whether the triggering of ECF K+ conservation by overnight low dietary K+ intake is prevented by parallel K+ supplementation via intragastric or intraportal infusion, which would be sensed by the hypothetical portal vein (or splanchnic) sensors, but not by K+ supplementation via systemic infusion. Aim 2. Test for a role of portal sensing of K+ intake in extracellular K+ homeostasis. We propose to test whether portal denervation ablates portal sensing of Kv intake and, if so, whether it impairs the acute and chronic regulation of ECF K+ homeostasis by delaying renal and extrarenal responses to altered K+ intake. Significance: This project will potentially identify an important, previously unknown regulator of ECF K+ homeostasis.