EFFECTS OF COBALT ON HEME-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 cel ls is diminished after exposure to cobalt chloride (50 or 100 mu M) fo r 18-36 h. The redox state of cytochrome c and cytochrome aa,, however , remains stable, indicating a particular affinity of cytochrome b for cobalt. Erythropoietin production of HepG2 cells increases after appl ication of cobalt chloride, whereas H2O2 production, as measured by th e dihydrorhodamine technique, decreases. It is concluded that cobalt s timulates a signal cascade with cytochrome b as receptor and H2O2 as s econd messenger for regulating erythropoietin production.