Comparison of Fluorescence Probes for Intracellular Sodium Imaging in Prostate Cancer Cell Lines

Sodium (Na) ions are known to regulate many signaling pathways involved in both physiological and pathological conditions. In particular, alterations in intracellular concentrations of Na and corresponding changes in membrane potential are known to be major actors of cancer progression to metastatic phenotype. Though the functionality of Na channels and the corresponding Na currents can be investigated using the patch-clamp technique, the latter is rather invasive and a technically difficult method to study intracellular Na transients compared to Na fluorescence imaging. Despite the fact that Na signaling is considered an important controller of cancer progression, only few data using Na imaging approaches are available so far, suggesting the persisting challenge within the scientific community. In this study, we describe in detail the approach for application of Na imaging technique to measure intracellular Na variations in human prostate cancer cells. Accordingly, we used three Na-specific fluorescent dyes-Na-binding benzofuran isophthalate (SBFI), CoroNa™ Green (Corona) and Asante NaTRIUM Green-2 (ANG-2). These dyes have been assessed for optimal loading conditions, dissociation constant and working range after different calibration methods, and intracellular Na sensitivity, in order to determine which probe can be considered as the most reliable to visualize Na fluctuations in vitro.