L-[3H]nitroarginine and L-[3H]arginine uptake into rat cerebellar synaptosomes: kinetics and pharmacology.
Characteristics of the transport of the nitric oxide synthase substrate L-arginine and its inhibitor, NG-nitro-L-arginine (L-NOARG), into rat cerebellar synaptosomes were studied. Uptake of both L-arginine and L-NOARG was linear with increasing amount of protein (up to 40 micrograms) and time of incubation (up to 5 min) at 37 degrees C. Uptake of both compounds reached a steady state by 20 min. Maximal uptake of L-NOARG (650 pmol/mg of protein) was three to four times higher than that of L-arginine (170 pmol/mg of protein). L-NOARG uptake showed biphasic kinetics (Km1 = 0.72 mM, Vmax 1 = 0.98 nmol/min/mg of protein; Km2 = 2.57 mM, Vmax2 = 16.25 nmol/min/mg of protein). L-Arginine uptake was monophasic with a Km of 106 microM and a Vmax of 0.33 nmol/min/mg of protein. L-NOARG uptake was selectively inhibited by L-NOARG, NG-nitro-L-arginine methyl ester, and branched-chain and aromatic amino acids. L-Alanine and L-serine also inhibited L-NOARG uptake but with less potency. Uptake of L-arginine was selectively inhibited by NG-monomethyl-L-arginine acetate and basic amino acids. These studies suggest that in rat cerebellar synaptosomes, L-NOARG is transported by the neutral amino acid carrier systems T and L with high affinity, whereas L-arginine is transported by the basic amino acid carrier system y+ with high affinity. These data indicate that the concentration of competing amino acids is an important factor in determining the rates of uptake of L-NOARG and L-arginine into synaptosomes and, in this way, may control the activity of nitric oxide synthase.
Rao
V L
VL
Neuroscience Research Unit, Hôpital St. Luc (University of Montreal), Quebec, Canada.
Butterworth
R F
RF
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics* / Q000494:pharmacology; D001692:Biological Transport / Q000502:physiology; D002531:Cerebellum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000493:pharmacokinetics; D007700:Kinetics; D008297:Male; D019331:NG-Nitroarginine Methyl Ester; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D019335:Nitroarginine; D051381:Rats; D017207:Rats, Sprague-Dawley; D012680:Sensitivity and Specificity; D013574:Synaptosomes / Q000378:metabolism*; D014316:Tritium; D019323:omega-N-Methylarginine
D000596:Amino Acids; D004791:Enzyme Inhibitors; D014316:Tritium; D019335:Nitroarginine; D019323:omega-N-Methylarginine; D001120:Arginine; D019001:Nitric Oxide Synthase; D019331:NG-Nitroarginine Methyl Ester