Regulation of L-arginine synthesis from L-citrulline by L-glutamine in endothelial cells.
L-Arginine synthesis from L-citrulline was studied in cultured bovine venular, bovine aortic, human microvascular, and cloned human microvascular endothelial cells (EC). L-Citrulline was actively recycled into L-arginine in all four EC lines, with similar rates between venular and aortic EC. L-Arginine synthesis from L-citrulline was very sensitive to extracellular L-citrulline concentrations in the range normally found in plasma (50-100 microM). L-Glutamine (0.5mM) decreased L-arginine synthesis from L-citrulline, whereas 0.5 mM L-arginine, L-alanine, L-glutamate, or L-lysine had no effect. In contrast to the findings in intact cells, 1 mM L-glutamine had no effect on L-arginine synthesis from L-citrulline in EC lysates. Similarly, L-glutamine (1 mM) had no effect on the conversion of argininosuccinate to arginine in EC lysates. L-Glutamine (0.5 and 1 mM), but not 0.5 mM L-arginine, L-alanine, L-glutamate, or L-lysine, inhibited L-citrulline transport by EC. The inhibition of L-citrulline transport by L-glutamine was dose dependent and competitive in nature. These results suggest that L-glutamine decreased L-arginine synthesis from extracellular L-citrulline by interfering with its transport. Inasmuch as nitric oxide (NO) and L-citrulline are constantly generated from L-arginine, with L-citrulline being actively converted into L-arginine in venular, microvascular, and aortic EC, our data indicate a functioning intracellular arginine-citrulline cycle in these cells. This cycle may function to efficiently scavenge the carbon and alpha-amino group of L-arginine and to maintain a sufficient cellular concentration of L-arginine during prolonged synthesis of NO in EC. (ABSTRACT TRUNCATED AT 250 WORDS)
Wu
G
G
Department of Animal Science, Texas A & M University, College Station 77843.
Meininger
C J
CJ
D000818:Animals; D001120:Arginine / Q000096:biosynthesis*; D001125:Argininosuccinic Acid / Q000378:metabolism; D001692:Biological Transport; D002417:Cattle; D002478:Cells, Cultured; D002956:Citrulline / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology / Q000378:metabolism*; D005973:Glutamine / Q000378:metabolism*; D006801:Humans
D005973:Glutamine; D001125:Argininosuccinic Acid; D002956:Citrulline; D001120:Arginine