A Highly Selective Mitochondria-Targeting Fluorescent K+ Sensor

Regulation of intracellular potassium (K+) concentration plays a key role in metabolic processes. So far, only a few intracellular K+ sensors have been developed. The highly selective fluorescent K+ sensor KS6 for monitoring K+ ion dynamics in mitochondria was produced by coupling triphenylphosphonium, borondipyrromethene (BODIPY), and triazacryptand (TAC). KS6 shows a good response to K+ in the range 30-500 mM, a large dynamic range (F-max/F-0 approximate to 130), high brightness (phi(f) = 14.4% at 150 mm of K+), and insensitivity to both pH in the range 5.5-9.0 and other metal ions under physiological conditions. Colocalization tests of KS6 with MitoTracker Green confirmed its predominant localization in the mitochondria of HeLa and U87MG cells. K+ efflux/influx in the mitochondria was observed upon stimulation with ionophores, nigericin, or ionomycin. KS6 is thus a highly selective semiquantitative K+ sensor suitable for the study of mitochondrial potassium flux in live cells.