A Highly Selective Mitochondria‐Targeting Fluorescent K⁺ Sensor

Abstract

Regulation of intracellular potassium (K+) concentration plays a key role in metabolic processes. So far only a few intracellular K+ sensors have been developed. We report here a highly selective fluorescent K+ sensor, KS6, synthesized for monitoring K+ ion dynamics in mitochondria by coupling triphenylphosphonium, borondipyrromethene (BODIPY), and triazacryptand (TAC). KS6 possesses good response to K+ in the range of 30–500 mM, large dynamic range (Fmax/F0: ~130), high brightness (ϕf: 14.4% at 150 mM of K+) and insensitivity to pH (5.5–9.0) and other metal ions under physiological conditions. Colocalization test of KS6 with MitoTracker Green confirmed its predominant localization in mitochondria of HeLa and U87MG cells. K+ efflux/influx in the mitochondria was observed in HeLa and U87MG cells upon stimulation with ionophores, nigericin or ionomycin. Therefore, KS6 is a highly selective semi-quantitative K+ sensor suitable for the study of mitochondrial potassium.

Discerning the Chemistry in Individual Organelles with Small‐Molecule Fluorescent Probes

“…Forexample,RhodZin-3 (3b,Scheme 2) reported by Gee and co-workers is now commercially available. [54] KS6 displayed anotable fluorescence enhancement (130-fold) in the presence of K + ,a nd has been successfully applied to study mitochondrial potassium flux in live cells. [53] In the absence of Hg 2+ ,the emission of RosHg was efficiently quenched (F < 0.005) by photoinduced electron transfer (PeT) from the electron-rich receptor (amine or sulfur) to the xanthene moiety.A remarkable increase in the fluorescence of RosHg was observed upon binding with Hg 2+ .C onfocal microscopy experiments demonstrated that this probe accumulated in mitochondria and could monitor changes in the Hg 2+ levels in the mitochondria of live cells.V ery recently,t he potent mitochondria-specific K + sensor KS6 (5, Scheme 2) for tracking K + dynamics was reported by Meldrum and co-workers.…”

Metal‐Cation Recognition in Water by a Tetrapyrazinoporphyrazine‐Based Tweezer Receptor

“…Cation binding by various synthetic receptors derived from crown ethers has been of interest in host–guest chemistry since the discovery of crown ethers by Pedersen in 1967 . Suitable supramolecular arrangements of crown ether analogues (such as cryptands,coronands, and lariat ethers) may provide an incredible tool for selective cation recognition. Among them, the tweezer (occasionally also called sandwich or clamshell) arrangement of two crown units has been shown to substantially increase the stability of the complex (i.e., association constant) and improve selectivity towards specific analytes .…”

Tracking intra‐ and inter‐organelle signaling of mitochondria

“…K þ mito dynamics are frequently measured via patch-clamp approaches using isolated mitochondria or mitoblasts [118,126,128,137]. A valuable alternative to investigate subcellular and especially K þ mito dynamics within single living cells is provided by fluorescent indicators [138][139][140]. These indicators represent small chemical dyes, either unspecifically labeling the whole cell or specifically localizing within mitochondria.…”

“…These indicators represent small chemical dyes, either unspecifically labeling the whole cell or specifically localizing within mitochondria. K + binding to the sensors results in an alteration of their fluorescence depending on the K + concentration [138][139][140]. Recently, the first GE indicators suitable for intracellular K + measurements have been developed [111,141].…”