title: Transport of D-[1-14C]-amino acids into Chinese hamster ovary (CHO-K1) cells: implications for use of labeled d-amino acids as molecular imaging agents.
abstract: BACKGROUND
  The fact that d-amino acids have been found in various tissues and are involved in various functions is a clue to how to develop new imaging agents. We examined d-amino acid transport mechanisms in Chinese hamster ovary (CHO-K1) cells because CHO-K1 cells are widely used in biomedical studies and are thought to be useful for expression of genes involved in metabolism of D-amino acids.
  
  
  METHODS
  Uptake experiments were performed. CHO-K1 cells cultured in 60-mm plastic culture dishes under ordinary culture conditions were incubated with 18.5 kBq of radiolabeled amino acid in 2 ml of phosphate-buffered-saline-based uptake solution at 37 degrees C. The following radiolabeled amino acid tracers were used: D-[1-(14)C]-alanine, L-[1-(14)C]-alanine, D-[1-(14)C]-serine, L-[1-(14)C]-serine, D-[1-(14)C]-methionine, L-[1-(14)C]-methionine, D-[1-(14)C]-phenylalanine, L-[1-(14)C]-phenylalanine, D-[1-(14)C]-leucine, L-[1-(14)C]-leucine, D-[1-(14)C]-valine, L-[1-(14)C]-valine, D-[1-(14)C]-tyrosine, L-[1-(14)C]-tyrosine, D-[1-(14)C]-glutamic acid, L-[1-(14)C]-glutamic acid, D-[1-(14)C]-lysine, L-[1-(14)C]-lysine, D-[1-(14)C]-arginine and L-[L-(14)C]-arginine. We tested the inhibitory effects of the following compounds (1.0 mM) on transport: 2-(methylamino)isobutyric acid (a specific inhibitor of system A, in Na(+)-containing uptake solution) and 2-amino-bicyclo[2,2,1]heptane-2-carboxylic acid (a specific inhibitor of system L, in Na(+)-free uptake solution).
  
  
  RESULTS
  D-[1-(14)C]-methionine, D-[1-(14)C]-phenylalanine and D-[1-(14)C]-tyrosine accumulated mainly via system L. D-[1-(14)C]-alanine and D-[1-(14)C]-serine accumulated primarily via system ASC. High uptake of D-[1-(14)C]-alanine, D-[1-(14)C]-methionine, D-[1-(14)C]-phenylalanine and D-[1-(14)C]-leucine was observed. The uptake of radiolabeled serine, valine, tyrosine, glutamic acid and arginine into CHO-K1 was highly stereoselective for l-isomers.
  
  
  CONCLUSIONS
  We observed high uptake of D-[1-(14)C]-alanine via system ASC (most likely alanine-serine-cysteine-selective amino acid transporter-1) and high uptake of D-[1-(14)C]-methionine and D-[1-(14)C]-phenylalanine via system L (most likely L-type amino acid transporter-1).
authors: Department of Radiological Sciences, Ibaraki Prefectural University of Health Sciences, 4669-2 Ami, Ami-machi, Inashiki-gun, Ibaraki 300-0394, Japan. sikano@ipu.ac.jp
authors: Naoto
authors: N
authors: Shikano
authors: Syuichi
authors: S
authors: Nakajima
authors: Takashi
authors: T
authors: Kotani
authors: Masato
authors: M
authors: Ogura
authors: Jun-Ichi
authors: J
authors: Sagara
authors: Yukio
authors: Y
authors: Iwamura
authors: Mitsuyoshi
authors: M
authors: Yoshimoto
authors: Nobuo
authors: N
authors: Kubota
authors: Nobuyoshi
authors: N
authors: Ishikawa
authors: Keiichi
authors: K
authors: Kawai
mesh_terms: D000596:Amino Acids / Q000493:pharmacokinetics*; D000818:Animals; D016466:CHO Cells; D002250:Carbon Radioisotopes; D006224:Cricetinae; D003412:Cricetulus; D007202:Indicators and Reagents; D007553:Isotope Labeling; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics*; D013237:Stereoisomerism
chemical_list: D000596:Amino Acids; D002250:Carbon Radioisotopes; D007202:Indicators and Reagents; D019275:Radiopharmaceuticals