Expression of large amino acid transporter LAT1 in rat brain endothelium

The expression of the large amino acid transporter, LAT1, was investigated in brain of adult Long-Evans rats. The LAT1 transcript was readily detected in brain microvessels and choroid plexus by reverse transcription polymera se chain reaction analysis using three different gene specific primer pairs . A polyclonal affinity purified antibody against the N-terminus of LAT1 wa s generated in chickens and used in immunoblot and immunocytochemical analy ses of brain tissue sections of adult rats. On immunoblots, the antibody de tected a peptide-inhibitable 45 kDa band in a rat brain microvessel membran e preparation. It also identified the same protein band in membrane prepara tions of different brain structures, as well as in heart and testis, wherea s the protein was absent or only faintly detectable in muscle, kidney, and liver. In brain sec tions, the antibody intensely labeled the luminal and a bluminal membranes of brain microvessel endothelial cells in all brain area s examined including cerebral cortex, cerebellum, hippocampus, and in gray and white matter regions. These results suggest that LAT1 is involved in tr anscellular transport and may play an important role in large, neutral amin o acid transfer across the blood-brain barrier.