Methylmercury-cysteine uptake by rat erythrocytes: evidence for several transport systems

The present study is a continuation of our experiments on methylmercury-cysteine (MeHg-cysteine) uptake by rat red blood cells (RBCs) at low temperature. Methylmercury-cysteine uptake by rat RBCs was conducted at 5 degrees C and 20 degrees C. The effects of Ca2+, colchicine, cytochalasin B, 4,4'-diisothiocyano-2,2'-stilbenedisulphonic acid (DIDS), N-ethylmaleimide (NEM), D-glucose, hexanol, L-homocysteine, ouabain, probenecid, sodium fluoride (NaF), vinblastine, and anisotonic changes on MeHg-cysteine uptake were examined. The results showed that MeHg-cysteine uptake at 5 degrees C could be described by Michaelis-Menten kinetics (v = VmaxS/(S+Km), where Km = 37.02 mM and Vmax = 320.84 mmol l-1 RBCs h-1), but MeHg-cysteine uptake at 20 degrees C could be described by Michaelis-Menten kinetics with a linear component (v = [VmaxS/(S + Km)] + KdS, where Km = 2.71 mM, Vmax = 250.72 mmol l-1 RBCs h-1, and Kd = 5.63 mM). Methylmercury-cysteine uptake was inhibited by colchicine, cytochalasin B, D-glucose, hexanol, NaF, NEM, ouabain, probenecid, vinblastine and 230 mosM hypotonicity but stimulated by Ca2+, DIDS, L-homocysteine and 460 mosM hypertonicity. The results in the present study suggest that MeHg-cysteine uptake by rat RBCs might be involved in the following three transport systems: an energy transport system sensitive to Ca2+, ouabain and NaF and subjected to Michaelis-Menten kinetics; an organic anion transport system sensitive to probenecid; and a facilitated diffusive transport for D-glucose sensitive to cytochalasin B. It is likely that most of the transport systems work at temperatures higher than 5 degrees C.