EVIDENCE FOR THE EXISTENCE OF A SODIUM-DEPENDENT GLUTATHIONE (GSH) TRANSPORTER - EXPRESSION OF BOVINE BRAIN CAPILLARY MESSENGER-RNA AND SIZE FRACTIONS IN XENOPUS-LAEVIS OOCYTES AND DISSOCIATION FROM GAMMA-GLUTAMYL-TRANSPEPTIDASE AND FACILITATIVE GSH TRANSPORTERS

Our laboratory previously has shown apparent carrier-mediated glutathi one (GSH) uptake across the blood-brain barrier (BBB) in two animal mo dels, In the present study, when Xenopus oocytes were injected with bo vine brain capillary mRNA expression of intact GSH, uptake was observe d after 3 days, When total mRNA was converted to cDNA and subfractiona ted with subsequent cRNA injection into oocytes, three distinct fracti ons (5, 7-8, and 11-12) expressed carrier-mediated intact GSH transpor t, Northern blot analysis established the presence of RcGshT, the prev iously 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 sulfobr omophthalein-GSH, neither of which affects RcGshT, The Na+-dependent G SH uptake kinetics exhibited high affinity (similar to 400 mu M) and l ow affinity (similar to 10 mM) components. Fraction 11 expressed Na+-i ndependent transport of intact GSH and also contained the GGT transcri pt, In conclusion, we have identified three distinct sized transcripts from bovine brain capillary mRNA which express GSH transport: one fra ction expresses a novel Na+-dependent GSH uptake which can be dissocia ted unequivocally from both GGT and RcGshT for the first time and whic h may account for uptake of GSH against its electrochemical gradient a t the BBB.