Glutathione redox potential in response to differentiation and enzyme inducers

The reduced glutathione (GSH)/oxidized glutathione (GSSG) redox state is th ought to function in signaling of detoxification gene expression, but also appears to be tightly regulated in cells under normal conditions. Thus it i s not clear that the magnitude of change in response to physiologic stimuli is sufficient for a role in redox signaling under nontoxicologic condition s. The purpose of this study was to determine the change in 2GSH/GSSG redox during signaling of differentiation and increased detoxification enzyme ac tivity in HT29 cells. We measured GSH, GSSG, cell volume, and cell pH, and we used the Nernst equation to determine the changes in redox potential E-h , of the 2GSH/GSSG pool in response to the differentiating agent, sodium bu tyrate, and the detoxification enzyme inducer, benzyl isothiocyanate. Sodiu m butyrate caused a 60-mV oxidation (from -260 to -200 mV), an oxidation su fficient for a 100-fold change in protein dithiols:disulfide ratio. Benzyl isothiocyanate caused a 16-mV oxidation in control cells but a 40-mV oxidat ion (to -160 mV) in differentiated cells. Changes in GSH and mRNA for gluta mate:cysteine ligase did not correlate with E-h; however, correlations were seen between E-h and glutathione S-transferase (GST) and nicotinamide aden ine dinucleotide phosphate (NADPH):quinone reductase activities (N:QR). The se results show that 2GSH/GSSG redox changes in response to physiologic sti muli such as differentiation and enzyme inducers are of a sufficient magnit ude to control the activity of redox-sensitive proteins. This suggests that physiologic modulation of the 2GSH/GSSG redox poise could provide a fundam ental parameter for the control of cell phenotype. (C) 1999 Elsevier Scienc e.