P-glycoprotein regulated transport of glutamate at blood-brain barrier

AIM: To study whether efflux of glutamate(Glu) at blood brain barrier(BBB) was regulated by P-glycoprotein(P-gp). METHODS: 1) After intracerebral microinjection [H-3]Glu 5 min, recoveries were determined in injected cerebrums in presence of multidrug-resistant (MDR) reversing agents verapamil(Ver), vincristine (VCR), and cyclosporin A(CsA); 2) apparent transfer constants (K-in) of [H-3]Glu from plasma to brain were determined after the in situ rat brain perfusion 2 min using solution containing MDR-reversing agents; 3) uptake amount of [H-3]Glu by primary cultured bovine brain capillary endothelial cells(BCEC) was analyzed; and 4) In presence of MDR-reversing agents and antibody of P-gp, C219, uptake amount of [H-3]Glu by luminal membrane vesicles derived from BCEC was also determined. RESULTS: In control rats, remaining percentage of [H-3] Glu in injected cerebrums was 25% +/- 16% at 5 min after intracerebral injection. After pre-treating with CsA 10, 100 mu mol.L-1, VCR 20 mu mol.L-1 and Ver 100 mu mol.L-1, the remaining percentages of [H-3]Glu were increased to about 2.2,2.5, 2.3, and 2.7 folds of control, respectively. In the in situ rat brain perfusion experiment, VCR and CsA in perfusion medium concentration-dependently increased [3H]Glu BBB permeability to brain. Go-administration of CsA 40 mu mol.L-1 made BBB permeability of [H-3]Glu in cerebral cortex, hippocampus and stratum increase to about 9, 3, 7, and 4.6 folds of control, respectively. Steady-state uptake of [H-3]Glu by BCEC was also increased up to 2.5 folds in presence of 100 mu mol.L-1 CsA. MDR-reversing agents and antibody of P-gp, C-219, level-dependently inhibited the uptake of [H-3]Glu by luminal membrane vesicles of BCEC. And this process is ATP-dependent. CONCLUSION: Efflux of Glu at BBB may be regulated by P-gp.