Cell-associated radioiron following exposure of cardiomyocytes to chelators. Primary cardiomyocytes were loaded with 0.36 mM ⁵⁹Fe (prepared from ⁵⁹Fe-chloride Amersham Radiochemical Centre, Amersham, England, and sterile ferric ammonium citrate to provide a concentration of 100 mg/mL elemental iron). Loading was for either 3 hours (right graphs) or 24 hours (left graphs) in medium with no serum and subsequently washed sequentially with cold medium containing serum, medium containing 100 μM DTPA for 30′, and resuspended either in medium with or without 30% fetal calf serum and the indicated concentrations of chelators (labels next to curves indicate chelator concentrations; S denotes presence of serum). After incubation at 37°C for various periods of time, the cells were washed extensively with cold medium and processed for counting radioactivity and protein, as described in “Materials and methods.” Each point represents the mean radioactivity ± SE (n = 3) associated with cells (in cpm) at the indicated time of incubation (h). The dotted lines represent the experimental lines of control (no chelator) with SD of ± 7% obtained identically as those treated with chelator.