P glycoprotein regulated transport of glutamate at blood brain barrier

To study whether efflux of glutamate (Glu) at blood brain barrier (BBB) was regulated by P-glycoprotein (P-gp).

1) After intracerebral microinjection [3H]Glu 5 min, recoveries were determined in injected cerebrums in presence of multidrug-resistant(MDR) reversing agents verapamil (Ver), vincristine(VCR), an d cyclosporin A(CsA); 2) apparent transfer constants (Kin) of [3H]Glu from plasma to brain were determined after the in situ rat brain perfusion 2 min us ing solution containing MDR-reversing agents; 3) uptake amount of [3H]Glu by prima ry cultured bovine brain capillary endothelial cells(BCEC) was analyzed; and 4) In presence of MDR-reversing agents and antibody of P-gp, C(219), uptake amount of [3H]Glu by luminal membrane vesicles derived from BCEC was also determined.

In control rats, remaining percentage of [3H]Glu in inject ed cerebrums was 25 %+/-16 % at 5 min after intracerebral injection. After pre-treating with CsA 10, 100 micromol/L, VCR 20 micromol/L and Ver 100 micromol/L, the remaining percentages of [3H]Glu were increased to about 2.2, 2.5, 2.3, a nd 2.7 folds of control, respectively. In the in situ rat brain per fusion experiment, VCR and CsA in perfusion medium concentration-dependently increased [3H]Glu BBB permeability to brain. Co-administration o f CsA 40 micromol/L mad e BBB permeability of [3H]Glu in cerebral cortex, hippocampus and striatum increase to about 9, 3, 7, and 4.6 folds of control, respectively. Steady-state uptake of [3H]Glu by BCEC was also increased up to 2.5 folds in presence of 100 micromol/L CsA. MDR-reversing agents and antibody of P-gp, C219, level-dependently inhibited the uptake of [3H]Glu by luminal membrane vesicles of BCEC. And this process is ATP-dependent.

Efflux of Glu at BBB may be regulated by P-gp.