PARALLEL REGULATION OF ARGININE TRANSPORT AND NITRIC-OXIDE SYNTHESIS BY ANGIOTENSIN-II IN VASCULAR SMOOTH-MUSCLE CELLS - ROLE OF PROTEIN-KINASE-C

Experiments were performed to characterize arginine transport in vascu lar smooth muscle cells (SMCs) and the effect of angiotensin II (Ang I I) on this process. In addition, the role of arginine transport in the cytokine-induced nitric oxide (NO) production was assessed. Arginine transport takes place through Na+-independent (approximate to 60%) and Na+-dependent pathways (approximate to 40%). The Na+-independent argi nine uptake appears to be mediated by system y(+) because of its sensi tivity to cationic amino acids such as lysine, ornithine and homoargin ine. The transport system was relatively insensitive to acidification of the extracellular medium. By contrast, the Na+-dependent pathway is consistent with system B-0,B-+ since it was inhibited by both cationi c and neutral amino acids (i.e., glutamine, phenylalanine, and asparag ine), and did not accept Li+ as a Na+ replacement. Treatment of SMCs w ith 100 nM Ang II significantly inhibited the Na+-dependent arginine t ransport without affecting systems y(+), A, and L. This effect occurre d in a dose-dependent manner (IC50 of 8.9 +/- 0.9 nM) and is mediated by the AT-1 receptor subtype because it was blocked by DUP 753, a non- peptide antagonist of this receptor. The inhibition of system B-0,B-by Ang II is mediated by protein kinase C (PKC) because it was mimicke d by phorbol esters (phorbol 12-myristate 13-acetate) and was inhibite d by staurosporine. Ang II also inhibited the IL-1 beta induced nitrit e accumulation by SMCs. This action was also inhibited by staurosporin e and reproduced with phorbol esters, suggesting a coupling between ar ginine uptake and NO synthesis through a PKC-dependent mechanism. Howe ver, arginine supplementation in the medium (10 mM) failed to prevent the inhibitory action of Ang IT on NO synthesis. These findings sugges t that although Ang II inhibits concomitantly arginine transport and N O synthesis in SMCs, the reduction of NO synthesis is not associated w ith alterations in the cellular transport of arginine.