Intracellular sodium concentration plays important roles in many cellular processes, but methods to analyze dynamic change of [Na⁺] in organelles of interest are still lacking. To address this problem, controlled localization of fluorescent Na⁺ probes is a key issue. In this work, we developed a protein-coupled Na⁺-sensitive fluorescent probe, HaloNa-1, which covalently labelled a HaloTag protein expressed at specific organelles in living cells. Fluorescence intensity of HaloNa-1 increased by approximately three-fold when complexed with Na⁺, and the dissociation constant was within physiological range. Notably, by conjugating a fluorescent protein to the HaloTag protein and using it as internal standard, one can reduce unwanted variation of probe fluorescence due to different cell volume, HaloTag expression level, etc. With this technique, we could observe elevation of intracellular [Na⁺] after ionophore stimulation with higher reliability than conventional sensors. We believe our probe is potentially useful to understand Na⁺ dynamics inside cells.

细胞内钠浓度在许多细胞过程中起着重要作用，但是仍然缺乏分析感兴趣细胞器中[Na ⁺ ]动态变化的方法。为了解决这个问题，荧光Na ⁺探针的受控定位是一个关键问题。在这项工作中，我们开发了一种蛋白质偶联的Na ⁺敏感荧光探针HaloNa-1，该探针共价标记了在活细胞中特定细胞器上表达的HaloTag蛋白。与Na ⁺复合时，HaloNa-1的荧光强度增加了大约三倍，并且解离常数在生理范围内。值得注意的是，通过将荧光蛋白与HaloTag蛋白缀合并用作内标，可以减少由于不同的细胞体积，HaloTag表达水平等导致的探针荧光的不必要变化。通过这种技术，我们可以观察到细胞内[Na离子载体刺激后，⁺ ]比常规传感器具有更高的可靠性。我们认为我们的探针可能有助于理解细胞内的Na ⁺动力学。