Fluorescence Imaging of Extracellular Potassium Ion Using Potassium Sensing Oligonucleotide

Area of Science:

• Biochemistry
• Molecular Biology
• Analytical Chemistry

Background:

• Accurate monitoring of potassium ion (K+) concentrations is crucial for understanding cellular processes.
• Existing methods for K+ detection can be limited in real-time cellular imaging applications.

Purpose of the Study:

• To develop and evaluate potassium-sensing oligonucleotide (PSO) derivatives for fluorescent detection of K+.
• To enable real-time imaging of intracellular and extracellular K+ concentrations, particularly on cell surfaces.

Main Methods:

• Synthesis of PSO derivatives, conjugating quadruplex structure-forming oligonucleotides with FRET-capable peptides.
• Evaluation of PSO performance, including K+ selectivity, binding affinity (Kd), and cellular localization strategies.
• Utilizing Förster Resonance Energy Transfer (FRET) chromophore pairs (FAM and TAMRA) for fluorescence detection.

Main Results:

• Developed PSO 1 demonstrated selective and reciprocal fluorescence changes in response to K+ concentrations.
• PSO derivatives exhibited high K+ selectivity, even in the presence of excess sodium ions (Na+), with Kd values in the 5-30 mM range.
• Successful cell surface localization of PSO derivatives was achieved using biotinylated concanavalin A or sulfo-NHS-biotin via streptavidin.

Conclusions:

• PSO technology provides a sensitive and selective method for fluorescent K+ detection in aqueous media.
• Modified PSOs are suitable for real-time imaging of cytoplasmic and extracellular K+ concentrations.
• PSO derivatives localized to the cell surface enabled successful fluorescence imaging of extracellular K+ during induced apoptosis.