Discrimination of transport systems for methylmercury-cysteine uptake in rat erythrocytes by inhibitors and other factors.

The transport systems for methylmercury-cysteine (MeHgCys) uptake by isolated erythrocytes from rats were studied at 5 degrees C. Probenecid was used to test the organic acid transport system at different concentrations. While inhibiting the organic acid transport system by probenecid (0.25 mM), the following agents were used to determine other transport systems for MeHgCys uptake: (1) ouabain and sodium fluoride (NaF) were used to test the active transport system; (2) 4,4'-diisothiocyano-2,2'-stilbenendisulphonic acid (DIDS) and N-ethylmaleimide (NEM) were used to test the C1-ion transort system; (3) colchicine and vinblastine were used t o test the microtubule system; (4) hexanol was used to test the protein-mediated trasport systems and the non-electrolyte diffusion; (5) valinomycin was used to test the effect of the membrane potential on MeHgCys uptake. Furthermore, the effects of NH4+, Li+ and Na+ in the buffer on MeHgCys uptake were examined with or without probenecid. The results showed that most of MeHgCys was transported by the organic acid transport system. Colchicine and vinblastine stimulated MeHgCys uptake. NH4+, Li+ and Na+ ions could stimulate MeHgCys uptake with or without probenecid. Meanwhile, a small amount of MeHgCys was transported by means of the non-electrolyte diffusion which was stimulated by hexanol. Furthermore, DIDS could stimulate MeHgCys uptake and the transport systems for MeHgCys uptake were sensitive to the membrane potential.