L-arginine transport in retinas from streptozotocin diabetic rats: correlation with the level of IL-1 beta and NO synthase activity

Abstract

Several evidences suggest that the pro-inflammatory cytokines IL-1 beta and the radical NO are implicated as effectors molecules in the pancreatic beta-cells dysfunction; an event preceding the pathogenesis of diabetes. IL-1 beta induces the expression of the inducible isoform of NO synthase (iNOS), which use L-arginine as substrate to overproduce NO. However, it is not known whether these events may participate in the development of diabetic retinopathy, which is the main cause of blindness. In this work, we found an increased level of IL-1 beta in retinas from streptozotocin-induced (STZ) diabetic rats. We also observed that the activity of the NO synthase (NOS) and the L-arginine uptake are enhanced in retinas from STZ-induced diabetic rats as compared to retinas from control rats. We found that the uptake of L-arginine in retinas from control and diabetic rats occurs through a transporter resembling the Y + system, i.e. it is saturable, not affected over the pH range 6.5 to 7.4, and is independent of the extracellular Na+. Nevertheless, the L-arginine transport in retinas from diabetic rats occurs through a carrier with lower affinity (K(m) = 25 microM) and higher capacity (Vmax = 295 +/- 22.4 pmol L-arginine/mg protein) than in retinas from control rats (K(m) = 5 microM and Vmax = 158 +/- 12.8 pmol L-arginine/mg protein) which is correlated with the increased NOS activity and consequent depletion of the intracellular pool of L-arginine.