Submitted on March 19, 2007
Accepted on June 12, 2007
Control of extracellular cysteine/cystine redox state by HT29 cells is independent of cellular glutathione
Corinna L. Anderson1, Smita S. Iyer2, Thomas R Ziegler3, and Dean P. Jones3*
1 Graduate Program of Nutrition and Health Science, Emory University, Atlanta, Georgia, United States
2 Graduate Program of Nutrition and Health Science, Emory University, Atlanta, Georgia, United States; Department of Medicine, Emory University, Atlanta, Georgia, United States
3 Department of Medicine, Emory University, Atlanta, Georgia, United States
* To whom correspondence should be addressed. E-mail: dpjones{at}emory.edu.
Human cell lines regulate the redox state (Eh) of the cysteine/cystine (Cys/CySS) couple in culture media to approximately -80 mV, a value similar to the average Eh for Cys/CySS in human plasma. The mechanisms involved in regulation of extracellular Eh Cys/CySS are not known, but GSH is released from tissues at rates proportional to tissue GSH concentration, and this released GSH could react with CySS to contribute to maintenance of this balance. The present study was to determine whether depletion of cellular GSH altered regulation of extracellular Cys/CySS redox state. Decrease of GSH in HT29 cells by inhibiting synthesis with buthionine sulfoximine showed no effect on the rate of reduction of extracellular CySS to achieve a stable Eh for Cys/CySS in the culture media. Limiting Cys and CySS in the culture media also substantially decreased cellular GSH but resulted in no significant effect on extracellular Cys/CySS redox state. Addition of CySS to these cells showed that extracellular Cys/CySS redox state approached -80 mV at 4 h while cellular GSH and extracellular GSH/GSSG redox recovered more slowly. Taken together, these results show that HT29 cells have the capacity to regulate the extracellular Cys/CySS redox state by mechanisms that are independent of cellular GSH. The results suggest that transport systems for Cys and CySS and/or membranal oxidoreductases could be more important than cellular GSH in regulation of extracellular Cys/CySS redox state.
