Erythrocyte L-arginine uptake in peritoneal dialysis patients changes over time.

During long-term exposure to continuous ambulatory peritoneal dialysis (PD), the characteristics of the peritoneal membrane may be altered. The substrate for nitric oxide synthesis is L-arginine, which may enter cells via the y+ and y+L transport systems. Peritoneal membrane characteristics may depend on vascular function and the L-arginine-NO pathway. Maximal capacity for L-arginine transport is higher in patients with a lower dialysis adequacy index. Our aim was to evaluate erythrocyte L-arginine uptake in PD patients at the start and end of a 3-year interval. Our longitudinal study evaluated 8 stable patients on PD who were not using NO donors and who had been free of peritonitis for at least 1 month. Uptake of L-arginine was measured in 2003 and again in 2006. Maximal transport capacity (Vmax, in micromoles per liter-cells per hour) and half-saturation constant (km, in micromoles per liter) were measured in erythrocytes using 14C as a marker and N-ethylmaleimide as inhibitor of the y+ system. For the years 2003 and 2006 respectively, mean +/- standard deviation for total L-arginine uptake Vmax was 749 +/- 182 micromol/L-cells/h and 1146 +/- 365 micromol/L-cells/h (p = 0.016, paired t-test),for y+L Vmax was 180 +/- 58 micromol/L-cells/h and 515 +/- 142 micromol/L-cells/h (p = 0. 002), and for y+ Vmax was 556 +/- 177 micromol/L-cells/h and 662 +/- 267 micromol/ L-cells/h (nonsignificant). The total y+L and y+km were not significantly different. The L-arginine maximal uptake capacity in erythrocytes increased after 3 years of PD treatment. These findings agree with the suggestion of an association between y+L activity and dialysis adequacy or uremia toxicity. Peritoneal membrane characteristics may depend on vascular function and the L-arginine-NO pathway.

Erythrocyte L-arginine uptake in peritoneal dialysis patients: systems y and y+ L.

L-Arginine is the substrate for nitric oxide synthesis and may enter cells by the y+ and y+ L transport systems. Peritoneal membrane characteristics may depend on vascular function and the L-arginine-nitric oxide pathway. In a cross-sectional study, we evaluated erythrocyte L-arginine uptake in stable peritoneal dialysis (PD) patients with various categories of peritoneal transport function. We used 14C as a marker and N-ethyl-maleimide as an inhibitor of the y+ system to measure maximal uptake capacity (Vma in ulmol/L cell/h) and the half-saturation constant (Km in micromol/L) in erythrocytes. The sample consisted of 41 patients (mean age: 50 +/- 17 years; 5 with diabetes; 18 men). Mean dialysate-toplasma creatinine (D/P(Cr)) was 0.62 +/- 0.14. Peritoneal membrane transport was classified as high, high-average, low-average, or low in 10, 11, 11, and 9 patients, respectively. Mean y+ L Vmax, was 208 +/- 111 micromol/L cell/h, 494 +/- 893 micromol/L cell/h, 222 +/- 59 micromol/L cell/h, and 193 +/- 63 umol/L cell/h [p = 0.404, analysis of variance (ANOVA)] for the high, high-average, low-average, and low transporters respectively. Similarly, mean y+ Vmax was 963 +/- 1034 micromol/L cell/h 843 +/- 366 micromol/L cell/h, 639 +/- 254 micromol/L cell/h, and 774 +/- 378 micromol/L cell/h (p = 0.647, ANOVA). As with Vmax, the y+ L Km and y+ Km values were not significantly different between the various peritoneal transport categories. A negative correlation was observed between y+ Vmax and Kt/V (r = -0.393, p = 0.011). Erythrocyte uptake of L-arginine does not vary with peritoneal membrane transport characteristics, but maximal L-arginine uptake capacity is higher in patients with a lower Kt/V.