Expression of various multidrug resistance-associated protein (MRP) homologues in brain microvessel endothelial cells

Multidrug resistance-associated protein (MRP) actively transports a broad r ange of anionic compounds out of the cell. To date, six different homologue s of MRP (i.e. MRP1-MRP6) have been identified. The current study examines the expression of the various MRP homologues in both primary cultured bovin e brain microvessel endothelial cells (BBMEC) and the capillary-enriched fr action from bovine brain homogenates. RT-PCR analysis demonstrated the pres ence of MRP1, MRP4, MRP5 and MRP6 in both BBMEC and the capillary-enriched fractions of brain homogenates. While low levels of MRP3 were detected in t he BBMEC, it was not observed in the capillary-enriched fraction. In additi on, RT-PCR and Western blot studies indicated an absence of MRP3 expression in both blued-brain barrier preparations. The presence of several differen t MRP homologues in the brain microvessel endothelial cells may be importan t in controlling the permeability of the blood-brain barrier to organic ani ons. (C) 2000 Elsevier Science B.V. All rights reserved.