Calcium-Flux signal change

Calcium-bound Fura-2 is excited at 340/510 nm and the unbound form at 380/510 nm. Upon calcium-flux, the cytoplasm's calcium concentration increases, causing the fluorescence intensity at 340/510 nm to increase proportionately. In contrast, the 380/510 nm intensity declines in synchronization with the diminishing concentration of unbound dye. By ratioing fluorescence intensities produced by excitation at two wavelengths, artifacts associated with uneven dye distribution and cell number variation are minimized because they effect both measurements equally.