This measurement is a very rapid event which can be observed on the flow cytometer in real time given appropriate instrumentation. Accurate determination of intracellular calcium concentration can be made if aliquots of Indo-1 loaded cells are placed in solutions of various known calcium concentrations and treated with an ionophore such as Ionomycin. The properties of Indo-1 are well-described in the literature. Observations of the real time alteration in [Ca2+] can be performed using list mode on the flow cytometer.
