Differential regulation of glomerular arginine transporters (CAT-1 and CAT-2) in lipopolysaccharide-treated rats

The decrease in glomerular filtration rate (GFR) that is characteristic of sepsis has been shown to result from inhibition of glomerular endothelial nitric oxide synthase (eNOS) by nitric oxide (NO) generated from the inducible isoform of NOS (iNOS). Although L-arginine is the sole precursor for NO biosynthesis, its intracellular availability in glomeruli from septic animals has never been investigated. Arginine uptake was measured in freshly harvested glomeruli from the following experimental groups: 1) untreated rats; 2) rats pretreated with LPS (4 mg/kg body wt, 4 h before experiments); 3) rats treated with LPS as above with either L-N-6-(1-iminoethyl)lysine hydrochloride (L-NIL), a selective iNOS antagonist, or 7-nitroindazole, a selective neuronal NOS antagonist; and 4) rats treated with L-NIL only. Both glomeular and mesangial arginine transport characteristics were found compatible with a y(+) system. Arginine uptake was augmented in glomeruli from LPS-treated rats. Treatment with L-NIL completely abolished this effect whereas L-NIL alone had no effect. Similar results were obtained when primary cultures of rat mesangial cells were preincubated with LPS (10 mug/ml for 24 h) with or without L-NIL. Using RT-PCR, we found that in vivo administration of LPS resulted in a significant increase in glomerular cationic amino acid transporter-2 (CAT-2) mRNA expression whereas CAT-1 mRNA was undetected. Northern blotting further confirmed a significant increase in glomerular CAT-2 by LPS. In mesangial cells, the expression of both CAT-1 and CAT-2 mRNA was augmented after incubation with LPS. In conclusion, in vivo administration of LPS augments glomerular arginine transport through upregulation of steady-state CAT-2 mRNA while downregulating CAT-1 mRNA. These results may correspond to the changes in glomerular iNOS and eNOS activity in sepsis.