Evidence for the existence of a sodium-dependent glutathione (GSH) transporter. Expression of bovine brain capillary mRNA and size fractions in Xenopus laevis oocytes and dissociation from gamma-glutamyltranspeptidase and facilitative GSH transporters.

Our laboratory previously has shown apparent carrier-mediated glutathione (GSH) uptake across the blood-brain barrier (BBB) in two animal models. In the present study, when Xenopus oocytes were injected with bovine brain capillary mRNA expression of intact GSH, uptake was observed after 3 days. When total mRNA was converted to cDNA and subfractionated with subsequent cRNA injection into oocytes, three distinct fractions (5, 7-8, and 11-12) expressed carrier-mediated intact GSH transport. Northern blot analysis established the presence of RcGshT, the previously cloned sodium-independent hepatic canalicular transporter, only in fraction 5. GSH transport activity in fraction 7 was significantly inhibited by replacement of NaCl with choline chloride and by sulfobromophthalein-GSH, neither of which affects RcGshT. The Na(+)-dependent GSH uptake kinetics exhibited high affinity (approximately 400 micron) and low affinity (approximately 10 mM) components. Fraction 11 expressed Na(+)-independent transport of intact GSH and also contained the GGT transcript. In conclusion, we have identified three distinct sized transcripts from bovine brain capillary mRNA which express GSH transport: one fraction expresses a novel Na(+)-dependent GSH uptake which can be dissociated unequivocally from both GGT and RcGshT for the first time and which may account for uptake of GSH against its electrochemical gradient at the BBB.