The maintenance of K+ and Ca2+ homeostasis is crucial for many cellular functions. Potassium is accumulated in cells at high concentrations, while the cytosolic level of calcium, to ensure its signalling function, is kept at low levels and transiently increases in response to stresses. We examined Ca2+ homeostasis and Ca2+ signalling in Saccharomyces cerevisiae strains lacking plasma-membrane K+ influx (Trk1 and Trk2) or efflux (Tok1, Nha1 and Ena1-5) systems. The lack of K+ exporters slightly increased the cytosolic Ca2+, but did not alter the Ca2+ tolerance or Ca2+-stress response. In contrast, the K+-importers Trk1 and Trk2 play important and distinct roles in the maintenance of Ca2+ homeostasis. The presence of Trk1 was vital mainly for the growth of cells in the presence of high extracellular Ca2+, whilst the lack of Trk2 doubled steady-state intracellular Ca2+ levels. The absence of both K+ importers highly increased the Ca2+ response to osmotic or CaCl2 stresses and altered the balance between Ca2+ flux from external media and intracellular compartments. In addition, we found Trk2 to be important for the tolerance to high KCl and hygromycin B in cells growing on minimal media. All the data describe new interconnections between potassium and calcium homeostasis in S. cerevisiae.

中文翻译：

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K+ 特异性输入蛋白 Trk1 和 Trk2 在酿酒酵母细胞中的 Ca2+ 稳态和信号传导中发挥不同的作用

维持 K+ 和 Ca2+ 稳态对于许多细胞功能至关重要。钾以高浓度在细胞中积累，而细胞溶质中的钙，以确保其信号传导功能，保持在低水平，并在压力下瞬时增加。我们检查了缺乏质膜 K+ 流入（Trk1 和 Trk2）或流出（Tok1、Nha1 和 Ena1-5）系统的酿酒酵母菌株中的 Ca2+ 稳态和 Ca2+ 信号传导。K+ 输出者的缺乏略微增加了细胞溶质 Ca2+，但并未改变 Ca2+ 耐受性或 Ca2+-应激反应。相比之下，K+ 输入蛋白 Trk1 和 Trk2 在维持 Ca2+ 稳态中发挥着重要而独特的作用。Trk1 的存在主要对细胞在高细胞外 Ca2+ 存在下的生长至关重要，而 Trk2 的缺乏使稳态细胞内 Ca2+ 水平加倍。两个 K+ 输入源的缺失极大地增加了 Ca2+ 对渗透或 CaCl2 胁迫的反应，并改变了来自外部介质和细胞内隔室的 Ca2+ 通量之间的平衡。此外，我们发现 Trk2 对于在基本培养基上生长的细胞对高 KCl 和潮霉素 B 的耐受性很重要。所有数据都描述了酿酒酵母中钾和钙稳态之间的新联系。