Molecular and functional identification of large neutral amino acid transporters LAT1 and LAT2 and their pharmacological relevance at the blood-brainbarrier

We present here the evidence of molecular and functional expression of LAT1 and LAT2, subunits of the large neutral amino acid transporter system L, i n cultured brain capillary endothelial cells of the rat. By means of the RT -PCR method, transcripts of LAT1, LAT2 and heavy chain of 4F2 antigen (4F2h c) were detected in rat primary cultured brain capillary endothelial cells (BCECs) and immortalized subline, RBEC1. The uptake properties of RBEC1, su ch as [H-3] leucine and L-[H-3]DOPA uptake, were similar to those of primar y cultured BCECs. So, RBEC1 may retain almost native properties of the larg e neutral amino acid uptake activities. [H-3] Leucine uptake by RBEC1 showe d two saturable components a nd the K-m va lues of the high- and low-affini ty components were 8.92 +/-3.18 and 119 +/- 45 muM, respectively. The K-m v alue of the high-affinity component agreed well with that of LAT1 and the a mino acid transport selectivity of RBEC1 was similar to that of LAT1. There fore, it is suggested that LAT1 is important at the blood-brain barrier of rats. Additionally, the K-m value of the low-affinity component was similar to that of LAT2. These observations indicate that LAT1 and LAT2 are involv ed as transporters for large neutral amino acids at the blood-brain barrier . Additionally, we concluded that RBEC1 is useful as an in-vitro model for evaluation of the pharmacological relevance of system L at the blood-brain barrier.