METHYLMERCURY EFFLUX FROM BRAIN CAPILLARY ENDOTHELIAL-CELLS IS MODULATED BY INTRACELLULAR GLUTATHIONE BUT NOT ATP

To reach its target tissue, methylmercury must traverse brain capillar y endothelial cells, the site of the blood-brain barrier. Methylmercur y uptake from blood plasma into these cells is mediated in part by an amino acid carrier that transports the methylmercury-L-cysteine comple x; however, the mechanism by which it is released from the endothelial cells into brain interstitial space is unknown. Using bovine brain ca pillary endothelial cells in culture, the present study examined the h ypothesis that methylmercury is transported out of these cells as a gl utathione (GSH) complex GSH concentration in cultured bovine brain cap illary endothelial cells was 13.1 +/- 3.3 nmol/mg protein. Depletion o f intracellular GSH in [Hg-203]methylmercury-preloaded cells by exposu re to 1-chloro-2,4-dinitrobenzene or diethyl maleate decreased the rat e of [Hg-203]methylmercury efflux. Incubation of [Hg-203]methylmercury -preloaded cells with high concentrations of S-methylglutathione, S-et hylglutathione, S-butylglutathione, and sulfobromophthalein-glutathion e inhibited [Hg-203]methylmercury efflux. The GSH analogs gamma-glutam ylglycylglycine and ophthalmic acid also inhibited [Hg-203]methylmercu ry efflux, but to a lesser degree than the glutathione S-conjugates, w hereas L-leucine, L-methionine, and L-alanine had no effect. Efflux wa s not affected by depletion of intracellular ATP with 2-deoxyglucose o r antimycin A. These results indicate that complexation with GSH and s ubsequent transport of the complex by an ATP-independent mechanism may be involved in the transport of methylmercury out of brain capillary endothelial cells. (C) 1996 Academic Press Inc.