INTERLEUKIN-1-BETA AND TUMOR-NECROSIS-FACTOR-ALPHA STIMULATE THE CAT-2 GENE OF THE L-ARGININE TRANSPORTER IN CULTURED VASCULAR SMOOTH-MUSCLE CELLS

The production of nitric oxide (NO) from L-arginine by nitric oxide sy nthase (NOS) in cytokine-stimulated vascular smooth muscle cells (VSMC ) is thought to play an important role in the pathophysiology of sever al vascular disease states including septic shock. This study examines the relationship between cytokine-stimulated NO production and L-argi nine transport in cultured VSMC. Cultured VSMC from rat aorta were sti mulated with interleukin-1 beta, tumor necrosis factor-alpha, and/or a ngiotensin II (Ang II); and the accumulation of nitrite, a stable prod uct of NO metabolism, in the culture media and the rates of net L-argi nine uptake were measured. Interleukin-1 beta and tumor necrosis facto r-alpha, alone or in combination, stimulated both the uptake of L-argi nine and the accumulation of nitrite in the culture media in a dose-de pendent manner. Inhibition of NOS activity by substituted analogues of L-arginine had no effect on cytokine-stimulated L-arginine transport. Ang II in the presence of cytokines up-regulated L-arginine transport while inhibiting nitrite accumulation. Two forms of the L-arginine tr ansporter, cat-1b and cat-2, are expressed in VSMC. Northern analysis revealed that the cytokine-stimulated increase in L-arginine transport coincided with increased levels of cat-2 mRNA. In contrast, cat-1b do es not appear to be regulated by cytokines at the mRNA level, although significant increases in response to Ang II were observed. These resu lts show that, while cytokines can stimulate both NOS activity and L-a rginine uptake, NO production is not required to signal the increase i n L-arginine transport. Furthermore, Ang II and cytokine stimulation o f L-arginine uptake involves the differential regulation of the cation ic amino acid transporter (cat) genes.