Inhibition of nitric oxide synthase abrogates lipopolysaccharides‐induced up‐regulation of L‐arginine uptake in rat alveolar macrophages

It was tested whether the inducible nitric oxide synthase (iNOS) pathway might be involved in lipopolysaccharides‐(LPS)‐induced up‐regulation of L ‐arginine transport in rat alveolar macrophages (AMΦ). AMΦ were cultured in absence or presence of LPS. Nitrite accumulation was determined in culture media and cells were used to study [ 3 H]‐ L ‐arginine uptake or to isolate RNA for RT – PCR. Culture in presence of LPS (1 μg ml −1 , 20 h) caused 11 fold increase of nitrite accumulation and 2.5 fold increase of [ 3 H]‐ L ‐arginine uptake. The inducible NO synthase (iNOS) inhibitor 2‐amino‐5,6‐dihydro‐6‐methyl‐4 H ‐1,3‐thiazine (AMT) present alone during culture had only marginal effects on [ 3 H]‐ L ‐arginine uptake. However, AMT present during culture additionally to LPS, suppressed LPS‐induced nitrite accumulation and LPS‐stimulated [ 3 H]‐ L ‐arginine uptake in the same concentration‐dependent manner. AMT present only for the last 30 min of the culture period had similar effects on [ 3 H]‐ L ‐arginine uptake. AMT present only during the uptake period also inhibited LPS‐stimulated [ 3 H]‐ L ‐arginine uptake, but with lower potency. The inhibitory effect of AMT could not be opposed by the NO releasing compound DETA NONOate. LPS caused an up‐regulation of the mRNA for the cationic amino acid transporter CAT‐2B, and this effect was not affected by AMT. AMT (100 μ M ) did not affect L ‐arginine transport studied by electrophysiological techniques in Xenopus laevis oocytes expressing either the human cationic amino acid transporter hCAT‐1 or hCAT‐2B. In conclusion, iNOS inhibition in rat AMΦ abolished LPS‐activated L ‐arginine uptake. This effect appears to be caused by reduced flow of L ‐arginine through the iNOS pathway.British Journal of Pharmacology (2001) 133 , 379–386; doi: 10.1038/sj.bjp.0704091