Effect of extracellular ferritin on the LIP. Cellular LIP was measured with the fluorescent tracer calcein. DEC were incubated with 40 nmol/L H-rich holoferritin or apoferritin for 64 hours, beginning at day 6 of phase II or with medium only (control). Cells were loaded with 250 nmol/L calcein AM for 5 minutes at 37°C. Fluorescence was measured before and after chelation with 100 μmol/L SIH. Relative cellular LIP values are demonstrated.