Expression of multidrug resistance proteins (Mrps) in astrocytes of the mouse brain: a single cell RT-PCR study.

Multidrug resistance proteins (Mrps) are ATP-driven export pumps which mediate the export of organic anions such as glutathione conjugates and glucuronides from eukaryotic cells. Within the central nervous system astrocytes have important functions in metabolism and detoxification. In such processes Mrps play essential roles. To identify the Mrp repertoire of mouse brain and of astrocytes in particular, the expression of six mouse Mrps was investigated by reverse-transcription polymerase-chain reaction (RT-PCR). Using mouse brain mRNA as source, amplification products were obtained for Mrp1, Mrp3, Mrp4, Mrp5 and Mrp6. In contrast, mRNA of Mrp2 could not be detected in mouse brain. To investigate whether individual astrocytes express different Mrps in brain, single-cell RT-PCRs were performed from the cytosol harvested from single astrocytes in acutely isolated brain slices from cortex and cerebellum of TgN(GFAP-EGFP) mice. In these mice astrocytes can readily be identified by glial fibrillary acidic protein promoter-controlled green fluorescent protein expression. Investigation of individual cortical astrocytes and Bergmann glial cells revealed that these cells express Mrp1, Mrp4 and Mrp5 and that individual astrocytes can contain mRNA of one, two or three of these Mrps simultaneously.