Kinetics experiments are particularly useful for examining changes in DNA content, antibody binding, and calcium flux over time.  For example, calcium ions play an important role in cell signaling. The intracellular concentration of calcium ions often show transient changes in response to external stimuli. Several fluorescent dyes can be used to measure bound Ca++ by flow cytometry, including Indo-1 (which requires a UV laser) and a combination such as Fluo-3 and Fura Red, which can be used in instruments limited to excitation at 488 nm. Fluo-3 (with maximal fluorescence at 530 nm) increases its fluorescence with increasing Ca++ concentration. Fura Red (maximal fluorescence at 650 nm) decreases its fluorescence with increasing Ca++ concentration. The ratio of Fluo-3 to Fura Red fluorescence can be used to follow changes in Ca++ concentration over time.