Functional characterization of rat plasma membrane monoamine transporter in the blood-brain and blood-cerebrospinal fluid barriers

Abstract

This study investigated the expression and functional roles of rat plasma membrane monoamine transporter (rPMAT) in the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier by using in vitro brain barrier model cells (TR-BBB13 and TR-CSFB3 cells) and multiple in vivo experimental techniques. Quantitative reverse transcription-polymerase chain reaction analysis showed relatively high expression of rPMAT mRNA in TR-BBB13 and TR-CSFB3 cells. 1-Methyl-4-phenylpyridinium (MPP+) was transported into rPMAT-expressing cells in a sodium-independent manner. [3H]MPP+ was taken up concentration dependently by TR-BBB13 and TR-CSFB3 cells with Km values similar to that of rPMAT-expressing cells. [3H]MPP+ transports into these cells were markedly inhibited by serotonin, dopamine, and cationic drugs. rPMAT small interfering RNA (siRNA) significantly suppressed the [3H]MPP+ uptake by TR-BBB13 cells. Intracerebrally injected [3H]MPP+ was eliminated from the brain parenchymal region, whereas brain [3H]MPP+ uptake did not increase with time during in situ brain perfusion, suggesting that the brain-to-blood transport across the BBB predominates over the blood-to-brain transport. Brain microdialysis studies revealed that the elimination across the BBB was significantly decreased by coperfusion of unlabelled MPP+, serotonin, or dopamine. [3H]MPP+ was also eliminated from the CSF. These findings suggest that PMAT in brain barriers functions as the brain-to-blood transporter to regulate brain concentrations of organic cations including monoamines and cationic neurotoxins. © 2011 Wiley-Liss, Inc. and the American Pharmacists Association.