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Commun Biol. 2019 Jan 14;2:18. doi: 10.1038/s42003-018-0269-2. eCollection 2019.

Genetically encoded fluorescent indicators for imaging intracellular potassium ion concentration.

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1Department of Urology, Boston Children's Hospital, Department of Microbiology and Immunobiology, Department of Surgery, Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115 USA.
2Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2 Canada.
3Department of Physiology, University of Alberta, Edmonton, AB T6G 2H7 Canada.
4Department of Chemistry, The University of Tokyo, Tokyo, 113-0033 Japan.


Potassium ion (K+) homeostasis and dynamics play critical roles in biological activities. Here we describe three genetically encoded K+ indicators. KIRIN1 (potassium (K) ion ratiometric indicator) and KIRIN1-GR are Förster resonance energy transfer (FRET)-based indicators with a bacterial K+ binding protein (Kbp) inserting between the fluorescent protein FRET pairs mCerulean3/cp173Venus and Clover/mRuby2, respectively. GINKO1 (green indicator of K+ for optical imaging) is a single fluorescent protein-based K+ indicator constructed by insertion of Kbp into enhanced green fluorescent protein (EGFP). These indicators are suitable for detecting K+ at physiologically relevant concentrations in vitro and in cells. KIRIN1 enabled imaging of cytosolic K+ depletion in live cells and K+ efflux and reuptake in cultured neurons. GINKO1, in conjunction with red fluorescent Ca2+ indicator, enable dual-color imaging of K+ and Ca2+ dynamics in neurons and glial cells. These results demonstrate that KIRIN1 and GINKO1 are useful tools for imaging intracellular K+ dynamics.

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