Subcellular distribution of chelatable iron: a laser scanning microscopic study in isolated hepatocytes and liver endothelial cells

The pool of cellular chelatable iron ('free iron', 'low-molecular-weight ir on', the 'labile iron pool') is usually considered to reside mainly within the cytosol. For the present study we adapted our previously established Ph en Green method, based on quantitative laser scanning microscopy, to examin e the subcellular distribution of chelatable iron in single intact cells fo r the first time. These measurements, performed in isolated rat hepatocytes and rat liver endothelial cells, showed considerable concentrations of che latable iron, not only in the cytosol but also in several other subcellular compartments. In isolated rat hepatocytes we determined a chelatable iron concentration of 5.8 +/- 2.6 muM within the cytosol and of at least 4.8 muM in mitochondria. The hepatocellular nucleus contained chelatable iron at t he surprisingly high concentration of 6.6 +/- 2.9 muM. In rat liver endothe lial cells, the concentration of chelatable iron within all these compartme nts was even higher (cytosol, 7.3 +/- 2.6 muM; nucleus, 11.8 +/- 3.9 muM; m itochondria, 92-12.7 muM); in addition, chelatable iron (approx. 16 +/- 4 m uM) was detected in a small subpopulation of the endosomal/lysosomal appara tus. Hence there is an uneven distribution of subcellular chelatable iron, a fact that is important to consider for (patho)physiological processes and that also has implications for the use of iron chelators to inhibit oxidat ive stress.