Effects of cobalt on haem proteins of erythropoietin‐producing HepG2 cells in multicellular spheroid culture

The hypoxia‐induced increase of spectrophotometrically measured light absorption at 560 nm, considered as reduced cytochrome b , in HepG2 cells is diminished after exposure to cobalt chloride (50 or 100 μM) for 18–36h. The redox state of cytochrome c and cytochrome aa 3 , however, remains stable, indicating a particular affinity of cytochrome b for cobalt. Erythropoietin production of HepG2 cells increases after application of cobalt chloride, whereas H 2 O 2 production, as measured by the dihydrorhodamine technique, decreases. It is concluded that cobalt stimulates a signal cascade with cytochrome b as receptor and H 2 O 2 as second messenger for regulating erythropoietin production.