Quin-2 and fura-2 measure calcium differently

Several fluorescent probes have been used in the past to monitor and to measure intracellular calcium and calcium fluxes. The most widely used of these probes are those developed by Tsien. We address the markedly different values obtained when comparing Quin-2 (the original probe) with Fura-2 (a second-generation probe). In most cases the values for intracellular calcium have been considered to be interchangeable for the different probes. Using several different hematopoietic cell lines we show that in no case do the two probes yield equivalent values.