Palladium-Mediated Synthesis of a Near-Infrared Fluorescent K⁺ Sensor

Potassium (K⁺) exits electrically excitable cells during normal and pathophysiological activity. Currently, K⁺-sensitive electrodes and electrical measurements are the primary tools to detect K⁺ fluxes. Here, we describe the synthesis of a near-IR, oxazine fluorescent K⁺ sensor (K_NIR-1) with a dissociation constant suited for detecting changes in intracellular and extracellular K⁺ concentrations. K_NIR-1 treatment of cells expressing voltage-gated K⁺ channels enabled the visualization of intracellular K⁺ depletion upon channel opening and restoration of cytoplasmic K⁺ after channel closing