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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.

Author information

1
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.
2
2Department of Chemistry, University of Alberta, Edmonton, AB T6G 2G2 Canada.
3
3Department of Physiology, University of Alberta, Edmonton, AB T6G 2H7 Canada.
4
4Department of Chemistry, The University of Tokyo, Tokyo, 113-0033 Japan.

Abstract

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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