Cationic and Neutral Amino Acids Decrease NO in the Renal Vasculature

Abstract

To examine mechanisms whereby amino acids modulate nitric oxide (NO) production and blood flow in the renal vasculature, NO in the renal venous effluent of the isolated perfused rat kidney was quantified by chemiluminescence as amino acids were added to the perfusate (n=4/group). The addition of 10−4 M cationic amino acids (L-ornithine, L-lysine, or L-homoarginine) or neutral amino acids (L-glutamine, L-leucine, or L-serine) significantly decreased NO by 22–53% and increased renal vascular resistance by 32–68%. Anionic amino acids (L-glutamate or L-aspartate) did not alter either parameter. The effects of the cationic and neutral amino acids were attenuated with 10−3 M L-arginine (L-Arg) and prevented by endothelial removal or NO synthase inhibition. These observations were confirmed in cultured EA.hy926 endothelial cells (n>1000 cells/group) in which the cationic and neutral amino acids (10−4 M) significantly decreased NO by 67–78%, as assessed by DAF fluorescence. In addition, the inhibition of amino acid transport system y+ (cationic amino acid transporter 1) or y+L (CD98/4F2 heavy chain) by siRNA diminished the NO-depleting effects of these amino acids in the cultured cells. Finally, transport studies demonstrated that cationic or neutral amino acids in the extracellular space significantly stimulated efflux of L-Arg out of endothelial cells by 89–173% compared to control (n=4/group). These data demonstrate that cationic and neutral amino acids modulate NO and renal vascular resistance by stimulating the efflux of L-Arg out of endothelial cells by y+ or y+L transport mechanisms. Supported by HL-29587.