EXTRA-RENAL REGULATION OF POTASSIUM HOMEOSTASIS

描述（改编自申请人的摘要）：细胞外液（ECF） +}必须保持在一个狭窄的范围内。如果ECF +]福尔斯过低 （低钾血症），细胞膜增生，如果ECF +]增加太多 （高钾血症）细胞膜去极化，都破坏正常的电 兴奋性，并可能具有危及生命的心脏效应。肾脏和肌肉 共同维护ECF ]。低钾血症期间，肌肉ICF K为 重新分配以缓冲ECF的下降}。在高钾血症期间， 肌肉ICF，直到肾脏调整可以发生。这些重要的肌肉 特定的自我平衡过程才刚刚开始被理解， 分子水平。有证据支持肌肉钾流失的假设 在低钾血症期间，由于钠离子介导的活性K+内流减少而导致低钾血症。 泵（Na，KATP酶，NKA）抑制，高钾血症期间K+摄取是 由钠泵激活介导。我们的实验室已经确定，在低K+ 饮食中NKA亚基的丰度在同种型和肌肉特异性中被抑制 方式： 60- 95%的下降在a2，而不是1。采用一种新的K+钳技术， 最近表明，在K+限制的早期，在a2下降之前， 胰岛素刺激的K+摄取和胰岛素刺激的 NKA ct 2型泵从内体到质膜的再分布 （下午）。越来越多的证据表明，布美他尼敏感的Na，K，2C 1协同转运蛋白 也是肌肉K+内流的一个组成部分，因此， 钾的体内平衡总体目标是确定分子 在低钾血症期间负责挖掘肌肉K+储存的机制， 在K+恢复后，将过量的血浆+]清除到ICF库中，并 了解这些过程如何在一组临床相关的 范例红细胞中Na，K-ATPase同工型和NKCCI的贡献均高于红细胞中Na，K-ATPase同工型和NKCCI的贡献。 将采用房室分析研究氧化白色糖酵解肌肉 评估以下内容的方法：全身K+吸收，肌肉 钾离子特异性转运、亚细胞分布和活性 转运蛋白，以及K转运蛋白和mRNA的池大小调节 程度.目的1将检验假设，在K+期间K+向ECF的转移 限制是通过减少质膜（PM）表达， NKA α 2和NKCC 1与胰岛素刺激的K+摄取的抗性偶联， 这一过程在伴有慢性肾衰竭的尿毒症中发生改变。目的 2将测试假设，甲状腺激素或地塞米松，两者都是 增加NKA cx 2（可能还有NKCC 1），改变K+的肾外控制 荷尔蒙平衡目的3将检验以下假设： K+恢复期间的ICF（K+限制后）是由正常化介导的。 NKA α 2和NKCC 1两者的表面表达。实现这些目标将 确定负责挖掘和充实的细胞机制， 肌肉K+水库，这将，理想情况下，建议策略，以操纵 肌肉K储存在临床环境中。

DESCRIPTION (Adapted from the Applicant's Abstract): Extracellular fluid (ECF) +} must be maintained within a narrow range. If ECF +] falls too low (hypokalemia), cell membranes hyperpolarize, and if ECF +] increases too much (hyperkalemia) cell membranes depobrize, both disrupt normal electrical excitability and can have life threatening cardiac effects. Kidneys and muscle work in concert to maintain ECF ]. During hypokalemia muscle ICF K is redistributed to buffer the fall in ECF }. During hyperkalemia K+ is pumped into muscle ICF until renal adjustments can occur. These important muscle specific homeostatic processes are only beginning to be understood at the molecular level. Evidence supports the hypothesis that K loss from muscle during hypokalemia results from decreased active K+ influx mediated by sodium pump (Na,KATPase, NKA) inhibition, and that K+ uptake during hyperktilemia is mediated by sodium pump activation. Our lab has established that during low K+ diet abundance of NKA subunits are depressed in an isoform and muscle specific manner: 60-95 percent fall in a2, not a 1. Using a novel K+ clamp technique, we recently showed that early in K+ restriction, prior to fall in a2, there is a severe blunting of both insulin stimulated K+ uptake, and of insulin stimulated redistribution of NKA ct2 type pumps from endosomes to the plasma membrane (PM). Evidence is mounting that the bumetanide sensitive Na,K,2C1 cotransporter also accounts for a component of muscle K+ influx and, thus, could play a role in potassium homeostasis. The overall aims are to determine the molecular mechanisms responsible for tapping muscle K+ stores during hypokalemia, for clearing excess plasma +] into the ICF store after K+ restoration, and to understand how these processes are altered in a set of clinically relevant paradigms. The contribution of both Na,K-ATPase isoforms and NKCCI in both red oxidative white glycolytic muscle will be studied with a compartmental analysis approach in which the following are assessed: whole body K+ uptake, muscle specific K+ transport, subcellular distribution and activity of K+ transporters, and pool size regulation of K transporter protein and mRNA levels. Aim 1 will test the hypothesis that the shift of K+ to ECF during K restriction is mediated by decreased plasma membrane (PM) expression of both NKA a2 and NKCC1 coupled to resistance to insulin stimulated K+ uptake, and that this process is altered in uremia accompanying chronic renal failure. Aim 2 will test the hypothesis that thyroid hormone or dexamethasone, both of which increase NKA cx2 (and perhaps NKCC 1), alter extrarenal control of K+ horneostasis. Aim 3 will test the hypothesis that the uptake of K+ from ECF to ICF during K+ restoration (following K+ restriction) is mediated by normalizing surface expression of both NKA a2 and NKCC1. Accomplishing these aims will identify the cellular mechanisms responsible for tapping and repleting the muscle K+ reservoir, which will, ideally, suggest strategies to manipulate muscle K stores in clinical settings.