Sodium transport in red blood cells from dialyzed uremic patients

Studies on red blood cell (RBC) sodium (Na) transport in chronic renal failure have described abnormalities in the ouabain-sensitive Na, K pump. We now report Na transport in RBC using cation flux methodology, measuring both the ouabain-sensitive Na, K pump and the ouabain-insensitive Na, K cotransport (CoT) and Na, lithium (Li) countertransport (CTT) in 28 subjects on hemodialysis, eight subjects on chronic ambulatory peritoneal dialysis (CAPD) and 29 control subjects. Intracellular cation content and passive permeability of Na were also examined. Mean Na efflux through the ouabain-sensitive Na, K pump was not reduced in dialysis patients when compared to normal subjects, whether measured in fresh cells (1.41 +/- 0.05 vs. 1.30 +/- 0.03 mmole/liter RBC/hr; P less than 0.05) or in Na-loaded cells (7.10 +/- 0.24 vs. 6.90 +/- 0.22; NS). There was, however, a marked and uniform suppression of the CoT pathway in Na-loaded cells from dialysis patients versus controls (0.14 +/- 0.02 vs. 0.41 +/- 0.05 mmole/liter RBC/hr; P less than 0.001). Mean CTT activity, as measured by Li efflux, was not different between dialysis and normal subjects. Uremic and normal RBC had similar intracellular Na or K content as well as passive permeability for either ion. This indicates that intracellular cationic homeostasis is maintained, perhaps secondary to balanced changes in cationic flux activity through these transport pathways.