Characterization of neuronal amino acid transporters: uptake of nitric oxide synthase inhibitors and implication for their biological effects.
In the present study we investigated uptake of the nitric oxide (NO) synthase inhibitors NG-methyl-L-arginine and NG-nitro-L-arginine by the mouse neuroblastoma x rat glioma hybrid cell line NG108-15. Uptake of NG-methyl-L-arginine was characterized by biphasic kinetics (Km1 = 8 mumol/L, Vmax1 = 0.09 nmol x mg-1 x min-1; Km2 = 229 mumol/L, Vmax2 = 2.9 nmol x mg-1 x min-1) and was inhibited by basic but not by neutral amino acids. Uptake of NG-nitro-L-arginine followed Michaelis-Menten kinetics (Km = 265 mumol/L, Vmax = 12.8 +/- 0.86 nmol x mg-1 x min-1) and was selectively inhibited by aromatic and branched chain amino acids. Further characterization of the transport systems revealed that uptake of NG-methyl-L-arginine is mediated by system y+, whereas systems L and T account for the transport of NG-nitro-L-arginine. In agreement with these data on uptake of the inhibitors, L-lysine and L-ornithine antagonized the inhibitory effects of NG-methyl-L-arginine on bradykinin-induced intracellular cyclic GMP accumulation, whereas L-tryptophan, L-phenylalanine, and L-leucine interfered with the effects of NG-nitro-L-arginine. These data suggest that rates of uptake are limiting for the biological effects of NO synthase inhibitors.
Schmidt
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K
Institut für Pharmakologie und Toxikologie, Karl-Franzens-Universität Graz, Austria.
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Mayer
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D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors*; D026905:Amino Acid Transport Systems; D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D006152:Cyclic GMP / Q000378:metabolism; D051379:Mice; D009474:Neurons / Q000378:metabolism*; D009569:Nitric Oxide / Q000037:antagonists & inhibitors; D019001:Nitric Oxide Synthase; D019335:Nitroarginine; D014407:Tumor Cells, Cultured; D019323:omega-N-Methylarginine
D026905:Amino Acid Transport Systems; D000596:Amino Acids; D002352:Carrier Proteins; D019335:Nitroarginine; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases; D006152:Cyclic GMP