The methylmercury-L-cysteine conjugate is a substrate for the L-type large neutral amino acid transporter

Methylmercury (MeHg) is a potent neurotoxin. The mechanism(s) that governs MeHg transport across the blood-brain barrier and other biological membranes remains unclear. This study addressed the role of the L-type large neutral amino acid transporter, LAT1, in MeHg transport. Studies were carried out in CHO-k1 cells. Over-expression of LAT1 in these cells was associated with enhanced uptake of [¹⁴C]-MeHg when treated with l-cysteine, but not with the d-cysteine conjugate. In the presence of excess l-methionine, a substrate for LAT1, l-cysteine-conjugated [¹⁴C]-MeHg uptake was significantly attenuated. Treatment of LAT-1 over-expressing CHO-k1 cells with l-cysteine-conjugated MeHg was also associated with increased leakage of lactate dehydrogenase into the media as well as reduced cell viability measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. In contrast, knock-down of LAT1 decreased the uptake of l-cysteine-conjugated MeHg and attenuated the effects of MeHg on lactate dehydrogenase leakage and CHO-k1 cell viability. These results indicate that the MeHg-l-cysteine conjugate is a substrate for the neutral amino acid transporter, LAT1, which actively transports MeHg across membranes.