Purpose. To establish a method for isolating highly purified brain capillary endothelial cells (BCECs) from rat brain by using magnetic cell sorting, and clarify the expression levels of multidrug resistance-associated protein (Mrp) subtypes in these highly purified BCECs. Methods. The cells were prepared from the capillary enriched-fraction by enzyme digestion, and reacted with anti-PECAM-1 antibody. The cell sorting was performed by autoMACS. The mRNA levels were measured by quantitative real-time PCR analysis. Results. From five rats, 2.3 × 106 cells were isolated in the PECAM-1(+) fraction and the percentage of labeled cells in this was 85.9%. PECAM-1, claudin-5 and Tie-2 mRNA were concentrated in the PECAM-1(+) fraction compared with rat brain. The contamination by neurons and astrocytes was markedly less than in the brain capillary fraction prepared by the glass bead column method. Mrp1 and 4 were predominantly expressed in the PECAM-1(+) fraction at similar levels to Mdr1a. The mRNA levels of Mrp5 and 3 were 10.6 and 7.60% of that of Mrp1, respectively. Conclusions. This new purification method provides BCECs with less contamination by neural cells. In the isolated BCECs, Mrp1 and 4 are predominantly expressed, suggesting that they play an important role at the rat blood-brain barrier.
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