Uptake of methylmercury cysteine by rat erythrocytes at lower temperature

Methylmercury cysteine (MeHg-cysteine) uptake by rat erythrocytes (RBC) was undertaken at 5 and 20 degrees C. The effects of several amino acids, their derivatives, ATP, Na+, Mg2+ and membrane potential on MeHg-cysteine uptake were examined. The results showed that MeHg-cysteine uptake was temperature-dependent, Na(+)-dependent at 20 degrees C, partly Na(+)-dependent at 5 degrees C and Mg(2+)-dependent at 5 and 20 degrees C. The membrane potential had a very slight effect on MeHg-cysteine uptake. N-Acetyl-L-cysteine (AC), alanine, beta-alanine, cysteine sulphinic acid (CSA), gamma-aminobutyric acid (GABA), D-phenylalanine, phenylalanine, serine and taurine inhibited MeHg-cysteine uptake at 5 degrees C. Tryptophan both stimulated and inhibited at different sampling times at 5 degrees C. Glycine and methionine had stimulation at 5 degrees C. Aspartic acid, isoleucine, leucine and tyrosine had no effect on MeHg-cysteine uptake. GABA, D-phenylalanine and tryptophan lost their effects at 20 degrees C. The effects of glycine and serine had reversed at 20 degrees C. The half-time of MeHg-cysteine uptake was ca. 0.57 h at 5 degrees C and 0.23 h at 20 degrees C. Several amino acids and their derivatives had an influence on the half-times of MeHg-cysteine uptake. The present study suggested that MeHg-cysteine uptake by rat RBC at lower temperature involved several overlapping transport systems; the greatest contribution was likely to be due to system ASC. Direct evidence for system L in MeHg-cysteine uptake was not obtained in the present study.