L-cysteine uptake is stimulated by 1-chloro-2,4-dinitrobenzene in vitro in human erythrocytes

In previous studies, the transport of dinitrophenyl-glutathione from erythrocytes has been extensively investigated. However, the effect of treatment of erythrocytes with such xenobiotics on free-SH status of cells has not been well documented. Also, the effects of N-acetyl-L-cysteine or other-SH containing compounds on glutathione conjugate transport have not been investigated. The objectives of the present study were to investigate how the presence N-acetyl-L-cysteine and L-cysteine affect the free-SH status of 1-chloro-2,4-dinitrobenzene treated erythrocytes and how N-acetyl-L-cysteine or L-cysteine affects the rate of dinitrophenyl-glutathione conjugate transport form erythrocytes. Our results indicated that L-cysteine is more efficient than N-acetyl-L-cysteine in increasing the free-SH content of erythrocytes in the presence of 1-chloro-2,4-dinitrobenzene. At the end of 20 min of exposure, free-SH levels remained at 5.3 mumol/ml erythrocyte in the presence of L-cysteine. However, in the presence of N-acetyl-L-cysteine the free-SH level was 2 mumol/ml erythrocyte. In the absence of 1-chloro-2,4-dinitrobenze, L-cysteine uptake by erythrocytes was not efficient compared to N-acetyl-L-cysteine. The free-SH concentrations in the presence of N-acetyl-L-cysteine and L-cysteine, in this case were, 9 +/- 1 and 1.5 +/- 0.1 mumol/ml erythrocytes respectively. These results clearly suggest that 1-chloro-2,4-dinitrobenzene stimulates the L-cysteine uptake in eryhtrocytes by a mechanism not described before. Our results also indicated that 1-chloro-2,4-dinitrobenzene induced L-cysteine uptake is a Na+ and ATP dependent process. Replacement of NaCl with LiCl decreased the L-cysteine uptake by about 5-fold and in the presence of NaF decrease in L-cysteine uptake was about 2 fold. Our results conclude the presence of an in vitro L-cysteine uptake mechanism in erythrocytes stimulated by 1-chloro-2,4-dinitrobenzene.