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

Abstract

The pool of cellular chelatable iron ('free iron', 'low-molecular-weight iron', the 'labile iron pool') is usually considered to reside mainly within the cytosol. For the present study we adapted our previously established Phen Green method, based on quantitative laser scanning microscopy, to examine the subcellular distribution of chelatable iron in single intact cells for the first time. These measurements, performed in isolated rat hepatocytes and rat liver endothelial cells, showed considerable concentrations of chelatable 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 microM within the cytosol and of at least 4.8 microM in mitochondria. The hepatocellular nucleus contained chelatable iron at the surprisingly high concentration of 6.6+/-2.9 microM. In rat liver endothelial cells, the concentration of chelatable iron within all these compartments was even higher (cytosol, 7.3+/-2.6 microM; nucleus, 11.8+/-3.9 microM; mitochondria, 9.2+/-2.7 microM); in addition, chelatable iron (approx. 16+/-4 microM) was detected in a small subpopulation of the endosomal/lysosomal apparatus. 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 oxidative stress.

Perfusion-Perls and -Turnbull methods supplemented by DAB intensification for nonheme iron histochemistry: demonstration of the superior sensitivity of the methods in the liver, spleen, and stomach of the rat

“…In agreement with this view, recent studies based on quenching of the fluorescent transition metal indicator by chelatable iron and dequenching by iron chelators, demonstrated the presence of chelatable Fe (II) in the cytoplasm, nucleus, and mitochondria of isolated hepatocytes of the rat (Petrat et al 2001(Petrat et al , 2002. It is also possible that ubiquitous iron-sulfur proteins have iron in mixed oxidation states (Cotton et al 1999).…”

A New Ratiometric Fluorescent Probe for Detection of Fe2+ with High Sensitivity and Its Intracellular Imaging Applications

“…The optical cellular imaging associated with fluorescent probes has been an efficient approach for detection of Fe 2 + in living cells. However, the Fe 2 + fluorescent probes reported were mostly designed based on a fluorescence-quenching mechanism [12][13][14] and suffered from lower sensitivity. [13,15] Furthermore, fluorescence of Fe 2 + -sensing probes emitted in the UV/Vis region, [12][13][14][15][16] not only might cause biological damage, but also suffered from relatively high background fluorescence.…”

Mitochondria represent another locale for the divalent metal transporter 1 (DMT1)

“…21,22 Indeed, this mode has been suggested to account for iron toxicity due to non-transferrin-bound, DMT1-mediated cell-surface iron uptake by liver 23 and heart 24 under iron overload conditions. 22 Iron may then transit through the mitochondrial chelatable iron pool, 25,26 and subsequently be stored in mitochondrial ferritin 27 or used in heme 28,29 or ironsulfur cluster biosynthesis. 3 Another high-affinity substrate of DMT1 is manganese.…”