Characterization of 3-[(123)I]iodo-L-alpha-methyl tyrosine transport in astrocytes of neonatal rats.
3-[(123)I]Iodo-L-alpha-methyl tyrosine ((123)I-IMT) is used for diagnosis and monitoring of brain tumours by means of single-photon emission tomography. As recently shown, (123)I-IMT is predominantly mediated into rat C6 glioma cells by sodium-independent system L for large neutral amino acids. Until now, (123)I-IMT transport in non-neoplastic glial cells has not been examined. Therefore, the aim of this study was to examine the cellular pathways and precise transport kinetics of (123)I-IMT uptake into astrocytes of neonatal rats. In particular sodium-independent (123)I-IMT transport into neonatal astrocytes was compared with sodium-independent (123)I-IMT uptake into neoplastic rat C6 glioma cells. Competitive inhibition experiments showed that (123)I-IMT is exclusively transported via sodium-independent system L into the neonatal astrocytes (92%). Kinetic analysis of sodium-independent (123)I-IMT uptake into neonatal astrocytes and into C6 glioma cells revealed apparent Michaelis constants K(M) = 13.9 +/- 0.5 microM and K(M) = 33.9 +/- 4.1 microM, respectively, which are in the same range of K(M) values as those recently determined for amino acid transport into neoplastic and non-neoplastic glial cells. Indeed, the K(M) values in the micromolar range correspond to the expression of the LAT-1 subunit of system L both in the neonatal astrocytes and in C6 glioma cells. However, sodium-independent maximum transport velocities (V(max)) differed significantly between neonatal astrocytes and C6 glioma cells (11.1 +/- 0.3 and 39.9 +/- 3.3 nmol/mg protein/10 min, respectively).
Kopka
K
K
Department of Nuclear Medicine, Westfälische Wilhelms-Universität Münster, Germany. kopka@uni-muenster.de
Riemann
B
B
Friedrich
M
M
Winters
S
S
Halfter
H
H
Weckesser
M
M
Stögbauer
F
F
Ringelstein
E B
EB
Schober
O
O
D026905:Amino Acid Transport Systems; D000598:Amino Acids, Cyclic / Q000378:metabolism / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism*; D001667:Binding, Competitive / Q000187:drug effects; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005910:Glioma / Q000175:diagnosis / Q000378:metabolism*; D007930:Leucine / Q000378:metabolism / Q000494:pharmacology; D008781:Methyltyrosines / Q000378:metabolism* / Q000493:pharmacokinetics*; D010649:Phenylalanine / Q000378:metabolism / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D019275:Radiopharmaceuticals; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D019805:alpha-Methyltyrosine / Q000378:metabolism / Q000494:pharmacology; D015091:beta-Alanine / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
D026905:Amino Acid Transport Systems; D000598:Amino Acids, Cyclic; D002352:Carrier Proteins; D008781:Methyltyrosines; D012333:RNA, Messenger; D019275:Radiopharmaceuticals; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; C006504:2-aminobicyclo(2,2,1)heptane-2-carboxylic acid; D010649:Phenylalanine; D019805:alpha-Methyltyrosine; C030855:3-iodo-alpha-methyltyrosine; D007930:Leucine