Intracellular chelation of iron with various chelators as monitored by fluorescence of J774 cells laden with CALG and CALB and quenched with externally added iron (online measurements). J774 cells labeled with either CALG (A) or CALB (B), loaded into the cytosol via their AM precursors as described in “Materials and methods,” were exposed to either FAS 20 μM or FeHQ 10 μM for up to 10 minutes and subsequently to DTPA 100 μM for 2 to 5 minutes (to bind extracellular iron and stop further iron ingress) and to either none or the indicated concentration of chelator (in μM). At the end of the experiment, as indicated, all samples were also treated with 100 μM SIH. All incubations and perfusions were carried out at 37°C. The fluorescence measurements were carried out in a fluorescence plate reader with readings taken every minute. All experimental systems were run in triplicate, and the fluorescence intensity values were averaged and normalized to the initial fluorescence (insets). The half-time values of fluorescence recovery (t_1/2) for ICL obtained in FeHQ-loaded and FAS-loaded cells are given in panels A and B as a function of concentration (in μM) (gray areas), and those corresponding to DFP treatment are given in panel B superimposed on those of ICL treatment. (C) ICL670 comparative ability to chelate cytosolic labile iron pools in different cells (online measurements). The ability of ICL670 to access J774, H9C2, and HepG2 cells and chelate cytosolic iron was and is given in terms of half times (t_1/2) (minute) of CALB fluorescence recovery.