Changes in intra- and extracellular potassium ion (K + ) concentrations control many important cellular processes and related biological functions. However, our current understanding of the spatiotemporal patterns of physiological and pathological K + changes is severely limited by the lack of practicable detection methods. We developed K + -sensitive genetically encoded, Förster resonance energy transfer-(FRET) based probes, called GEPIIs, which enable quantitative real-time imaging of K + dynamics. GEPIIs as purified biosensors are suitable to directly and precisely quantify K + levels in different body fluids and cell growth media. GEPIIs expressed in cells enable time-lapse and real-time recordings of global and local intracellular K + signals. Hitherto unknown Ca 2+ -triggered, organelle-specific K + changes were detected in pancreatic beta cells. Recombinant GEPIIs also enabled visualization of extracellular K + fluctuations in vivo with 2-photon microscopy. Therefore, GEPIIs are relevant for diverse K + assays and open new avenues for live-cell K + imaging.
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Bischof et al. (2017) studied this question.