Characterization of Neuronal Amino Acid Transporters: Uptake of Nitric Oxide Synthase Inhibitors and Implication for Their Biological Effects |
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Authors: | Kurt Schmidt Barbara M List Peter Klatt Bernd Mayer |
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Institution: | Institut für Pharmakologie und Toxikologie, Karl-Franzens-Universität Graz, Graz, Austria |
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Abstract: | Abstract: In the present study we investigated uptake of the nitric oxide (NO) synthase inhibitors N G-methyl- l -arginine and N G-nitro- l -arginine by the mouse neuroblastoma × rat glioma hybrid cell line NG108-15. Uptake of N G-methyl- l -arginine was characterized by biphasic kinetics ( K m1 = 8 µmol/L, V max1 = 0.09 nmol × mg?1× min?1; K m2 = 229 µmol/L, V max2 = 2.9 nmol × mg?1× min?1) and was inhibited by basic but not by neutral amino acids. Uptake of N G-nitro- l -arginine followed Michaelis-Menten kinetics ( K m = 265 µmol/L, V max = 12.8 ± 0.86 nmol × mg?1× min?1) and was selectively inhibited by aromatic and branched chain amino acids. Further characterization of the transport systems revealed that uptake of N G-methyl- l -arginine is mediated by system y+, whereas systems L and T account for the transport of N G-nitro- l -arginine. In agreement with these data on uptake of the inhibitors, l -lysine and l -ornithine antagonized the inhibitory effects of N G-methyl- l -arginine on bradykinin-induced intracellular cyclic GMP accumulation, whereas l -tryptophan, l -phenylalanine, and l -leucine interfered with the effects of N G-nitro- l -arginine. These data suggest that rates of uptake are limiting for the biological effects of NO synthase inhibitors. |
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Keywords: | Transport Nitric oxide synthase inhibitors Neuronal cell line Amino acids Cyclic GMP formation |
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