MENADIONE-RESISTANT CHINESE-HAMSTER OVARY CELLS HAVE AN INCREASED CAPACITY FOR GLUTATHIONE SYNTHESIS

A cell line (MRc40) resistant to the model quinone compound, menadione , has been isolated from a parental Chinese hamster ovary cell line (C HO-K1). The known relationship between menadione toxicity and glutathi one (GSH) depletion led us to investigate whether the mechanism of res istance of MRc40 was related to alteration in GSH homeostasis. Intrace llular concentrations of GSH and cysteine (CySH) were twofold and 3.2- fold greater in MRc40 than in CHO-K1. Following exposure to menadione, GSH and CySH were depleted, but subsequent recovery of thiols was mor e rapid and of greater magnitude in MRc40 than in CHO-K1. Twelve hours after exposure to menadione, the concentrations of GSH and CySH were 9.7- and 4.2-fold greater in MRc40 than in CHO-K1. Using nuclear magne tic resonance (NMR) spectroscopy, we observed the in situ removal of m enadione from cell suspensions of CHO-K1 and MRc40. However, only in C HO-K1 did we observe concomitant depletion of NMR-visible GSH. We conc lude that the perturbation of GSH metabolism contributes to the resist ant phenotype and is an important characteristic of menadione-resistan t CHO cells.