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.