Department of Physiology and Neuroscience, University of Southern California Keck School of Medicine, Los Angeles, CA 90089, USA.
Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.
Int J Mol Sci. 2024 Sep 6;25(17):9664. doi: 10.3390/ijms25179664.
Maintaining extracellular potassium (K) within narrow limits, critical for membrane potential and excitability, is accomplished through the internal redistribution of K between extracellular fluid (ECF) and intracellular fluid (ICF) in concert with the regulation of renal K output to balance K intake. Here we present evidence from high-precision analyses of stable K isotopes in rats maintained on a control diet that the tissues and organs involved in the internal redistribution of K differ in their speed of K exchange with ECF and can be grouped into those that exchange K with ECF either rapidly or more slowly ("fast" and "slow" pools). After 10 days of K restriction, a compartmental analysis indicates that the sizes of the ICF K pools decreased but that this decrease in ICF K pools was not homogeneous, rather occurring only in the slow pool (15% decrease, < 0.01), representing skeletal muscles, not in the fast pool. Furthermore, we find that the dietary K restriction is associated with a decline in the rate constants for K effluxes from both the "fast" and "slow" ICF pools ( < 0.05 for both). These results suggest that changes in unidentified transport pathways responsible for K efflux from ICF to ECF play an important role in buffering the internal redistribution of K between ICF and ECF during K restriction. Thus, the present study introduces novel stable isotope approaches to separately characterize heterogenous ICF K pools in vivo and assess K uptake by individual tissues, methods that provide key new tools to elucidate K homeostatic mechanisms in vivo.
维持细胞外钾 (K) 在狭窄范围内，这对膜电位和兴奋性至关重要，是通过 K 在细胞外液 (ECF) 和细胞内液 (ICF) 之间的内部重新分布来实现的，同时调节肾脏 K 输出以平衡 K 摄入。在这里，我们通过对正常饮食喂养的大鼠的稳定 K 同位素进行高精度分析，提供了证据，表明参与 K 内部再分布的组织和器官在与 ECF 交换 K 的速度上存在差异，可以分为与 ECF 快速或更缓慢地交换 K 的“快速”和“慢速”池。在限制 K 摄入 10 天后，一项分区分析表明，ICF K 池的大小减小，但 ICF K 池的这种减小不是均匀的，仅发生在慢速池中（减少 15%， < 0.01），代表骨骼肌，而不是快速池中。此外，我们发现饮食 K 限制与 K 从“快速”和“慢速”ICF 池的外流率常数下降有关（两者均 < 0.05）。这些结果表明，负责 K 从 ICF 到 ECF 外流的未识别转运途径的变化在缓冲 K 限制期间 ICF 和 ECF 之间 K 的内部再分布中起着重要作用。因此，本研究引入了新的稳定同位素方法，分别在体内对异质 ICF K 池进行特征分析，并评估单个组织的 K 摄取，这些方法为阐明体内 K 稳态机制提供了关键的新工具。
