Homocysteine Influx and Efflux: Participation of Erythrocytes in Homocysteine Homeostasis of the Plasma
One of the main objective of the present study was to determine if erythrocytes play a role in regulation of plasma homocysteine concentration. Another objective was to investigate if erythrocytes convert homocystine into homocysteine. In the present study, we exposed erytrocytes to different concentrations of homocysteine and then measured the nonprotein sulfhydryl (NPSH) concentrations. Erythrocytes treated in the same manner were later utilized for the homocysteine efflux studies. The effect of temperature on the influx and the efflux processes were also evaluated. We also determined the rate of homocysteine influx in the presence of different amino acids. The homocysteine influx studies demonstrated that erythrocytes can respond to increases in homocysteine concentration in the extracellular media and influx homocysteine in a concentration-dependent manner. NPSH concentrations in erythrocytes treated with 1 mM homocysteine reached to 1.47 ï½± 0.01 ìmol/ml erythrocyte in 1 h whereas this concentration reached to 2.01 ï½± 0.1 ìmol/ml erythrocyte in 3 mM homocysteine treated erytrocytes. The homocysteine efflux is also determined to be time-and concentration -dependent. Extracellular concentration of NPSH in 1 mM homocysteine pre-treated erythrocytes reached to 0.266 ï½± 0.02 ìmol/ml erythrocyte in 1 h whereas this concentration reached to 0.64 ï½± 0.01 ìmol/ml erythrocyte with 3 mM homocysteine pre-treated erythrocytes. Our results also indicate that erythrocytes convert extracellulary applied homocystine into homocysteine. Depending on our results, it could be concluded that eryhtrocytes may play a significant role in the regulation of plasma homocysteine homeostasis.