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Genetically encoded ratiometric indicators for potassium ion

By Yi Shen, Sheng-Yi Wu, Vladimir Rancic, Yong Qian, Shin-Ichiro Miyashita, Klaus Ballanyi, Robert E. Campbell, Min Dong

Posted 25 Jan 2018
bioRxiv DOI: 10.1101/254383

Potassium ion (K+) homeostasis and dynamics play critical roles in regulating various biological activities, and the ability to monitor K+ spatial-temporal dynamics is critical to understanding these biological functions. Here we report the design and characterization of a Förster resonance energy transfer (FRET)-based genetically encoded K+ indicator, KIRIN1, constructed by inserting a bacterial cytosolic K+ binding protein (Kbp) between a fluorescent protein (FP) FRET pair, mCerulean3 and cp173Venus. Binding of K+ induces a conformational change in Kbp, resulting in an increase in FRET efficiency. KIRIN1 was able to detect K+ at physiologically relevant concentrations in vitro and is highly selective toward K+ over Na+. We further demonstrated that KIRIN1 allowed real-time imaging of pharmacologically induced depletion of cytosolic K+ in live cells, and KIRIN1 also enabled optical tracing of K+ efflux and reuptake in neurons upon glutamate stimulation in cultured primary neurons. These results demonstrate that KIRIN1 is a valuable tool to detect K+ in vitro and in live cells.

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