Identification of the cationic amino acid transporter (System y+) of the rat blood-brain barrier.
Cationic amino acids are transported from blood into brain by a saturable carrier at the blood-brain barrier (BBB). The transport properties of this carrier were examined in the rat using an in situ brain perfusion technique. Influx into brain via this system was found to be sodium independent and followed Michaelis-Menten kinetics with half-saturation constants (Km) of 50-100 microM and maximal transport rates of 22-26 nmol/min/g for L-lysine, L-arginine, and L-ornithine. The kinetic properties matched that of System y+, the sodium-independent cationic amino acid transporter, the cDNA for which has been cloned from the mouse. To determine if the cloned receptor is expressed at the BBB, we assayed RNA from rat cerebral microvessels and choroid plexus for the presence of the cloned transporter mRNA by RNase protection. The mRNA was present in both cerebral microvessels and choroid plexus and was enriched in microvessels 38-fold as compared with whole brain. The results indicate that System y+ is present at the BBB and that its mRNA is more densely expressed at cerebral microvessels than in whole brain.
Stoll
J
J
Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892.
Wadhwani
K C
KC
Smith
Q R
QR
D000818:Animals; D001483:Base Sequence; D001812:Blood-Brain Barrier; D001921:Brain / Q000378:metabolism; D002196:Capillaries / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism*; D002560:Cerebrovascular Circulation; D002831:Choroid Plexus / Q000378:metabolism; D008297:Male; D008562:Membrane Glycoproteins; D008565:Membrane Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009693:Nucleic Acid Hybridization; D015345:Oligonucleotide Probes / Q000235:genetics; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011991:Receptors, Virus; D012260:Ribonucleases
D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D011991:Receptors, Virus; C070506:ecotropic murine leukemia virus receptor; D012260:Ribonucleases