Predominant functional activity of the large, neutral amino acid transporter (LAT1) isoform at the cerebrovasculature

In this study, we identify the predominant functional expression of the lar ge, neutral amino acid transporter (LAT1) isoform at the blood-brain barrie r (BBB). An in situ rat brain perfusion technique allowed perfusion of the radiotracer [C-14]-L-Leu (a ligand for both LAT1 and LAT2) alone or compete d with excess concentration of either LAT1 or LAT2 specific amino acids. Th e LAT2 specific amino acid, [C-14]-L-Asn, was perfused alone or with excess concentration of various amino acids. The brain uptake of [14C]-L-Leu was not significantly inhibited by LAT2 specific amino acids, but was inhibited significantly (up to 90%) by the LAT1 specific amino acid, D-Met. L-Asn di d not demonstrate saturable brain uptake. These data clearly demonstrate th at LAT1 is the functionally predominant isoform expressed at the BBB which is responsible for brain uptake of large, neutral amino acids. In addition, the functional activity of cerebrovascular LAT2 is insignificant, or absen t. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.