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

ABSTRACT

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.