Total and labile iron in the progressive iron accumulation model A:SH-SY5Y cells were grown for 8 days and then challenged for 2 days with different concentrations of iron (range 1.5–80 μM). B:total iron content determined by mass spectrometry. Increased level of iron in the culture media produced increased levels of intracellular iron. Data is mean ± SD of 4 independent determinations. C: The calcein-sensitive iron pool increased at 80 μM Fe compared with 7 μM Fe. Representative tracings are shown.