Transfer of iron from extracellular DFP-iron complexes to nuclei. H9C2 cells loaded with the nuclear iron sensor H-FlDFO were incubated with or without 5μM DFP-Fe complex (DFP:Fe ratio 3:1) and epifluorescent microscopic images were recorded every 5 minutes under settings for fluorescein. Representative fields of initial cell fluorescence at time 0 (A,C) and after incubation for 1 hour in the absence (B) or presence (D) of 5μM DFP-Fe complex. (E) Mean fluorescence values in r.u. plus or minus SD of 5 cells per field, calculated for each time-point image and normalized to the initial fluorescence (f/f₀), representing cells incubated without (None) and with 5μM DFP-Fe complex (DFP-Fe). Arrow indicates time the Fe complex was added. (F) Effect of DFP-Fe chelates (DFP:Fe at ratios of 1:1, 3:1, 5:1, 9:1) on the fluorescence (normalized to initial value, f₀, in r.u.) of 0.5μM H-FlDFO in solution (HBS buffer). The values of fluorescence intensity are means of triplicate samples run in parallel, plus or minus SEM.