Amino acids differentially inhibit the L-[3H]arginine transport and nitric oxide synthase in rat brain synaptosomes.
The nitric oxide synthase (NOS) present in the cytosol obtained from rat cerebral cortex synaptosomes was inhibited by NG-nitro-L-arginine (L-NOArg) with an IC50 value of approximately 0.06 microM. This compound did not affect the transport of L-arginine (L-Arg) into synaptosomes at concentrations up to 100 microM but other potential inhibitors of NOS (NG-monomethyl-L-arginine, NG-amino-L-arginine and L-arginine methyl ester) inhibited L-Arg transport at a concentration < 5 microM. We showed that concentrations of L-NOArg (0.001-3 microM) that did not block the uptake of tritiated arginine (L-[3H]Arg) inhibited the catalytic activity of NOS in intact synaptosomes. L-NOArg at a concentration of 1 microM inhibited the cytosolic enzyme by 98.0 +/- 2.0% of the total NOS activity whereas the enzyme studied in the intact synaptosomes was only inhibited by 75 +/- 5% which suggested that the NOS in synaptosomes is not fully accessible to the external L-NOArg. On the other hand, L-Lysine did not inhibit the cytosolic NOS activity of ruptured synaptosomes but at a concentration that blocked 50.0 +/- 4.5% of L-[3H]Arg uptake it inhibited the NOS activity in intact synaptosomes by 12.6 +/- 3.6%, suggesting that the transport of L-Arg may be an important regulatory step in the pathway for nitric oxide generation.
Lopes
M C
MC
Faculty of Pharmacy, University of Coimbra, Portugal.
Cardoso
S A
SA
Schousboe
A
A
Carvalho
A P
AP
D000594:Amino Acid Oxidoreductases / Q000037:antagonists & inhibitors*; D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D001921:Brain / Q000378:metabolism*; D002642:Chick Embryo; D003600:Cytosol / Q000378:metabolism; D009569:Nitric Oxide / Q000037:antagonists & inhibitors; D019001:Nitric Oxide Synthase; D019335:Nitroarginine; D051381:Rats; D017208:Rats, Wistar; D013574:Synaptosomes / Q000378:metabolism*; D014316:Tritium; D019323:omega-N-Methylarginine
D000596:Amino Acids; D014316:Tritium; D019335:Nitroarginine; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D001120:Arginine; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases