Erythrocyte sodium and potassium in patients on peritoneal dialysis

Intracellular sodium and potassium concentrations were determined on erythrocytes obtained, before and after treatment, from patients with end-stage renal disease undergoing 48-hour intermittent peritoneal dialysis. Erythrocyte sodium increased from 7.5 +/- 0.3 to 8.6 +/- 0.4 mmol/L cells with a mean of 1.1 +/- 0.1 mmol/L cells (P less than .001), but erythrocyte potassium and cellular water content were virtually unchanged. Plasma potassium decreased during dialysis from 4.2 +/- 0.2 to 3.3 +/- 0.1 mEq/L (P less than .001). The increase in red-cell sodium correlated with this decrease in plasma potassium (r = .51, P less than .01). In contrast, erythrocyte sodium and potassium in undialyzed control patients with chronic renal failure did not change over a similar period, and plasma potassium was unchanged (4.3 +/- 0.1 mEq/L before and 4.3 +/- 0.2 mEq/L after 48 hours). Incubation of postdialysis erythrocytes from the dialysis patients in their own plasma at varying potassium concentrations showed that the rise in cell sodium was blunted as the plasma potassium was increased from 3.2 +/- 0.1 to 4.5 +/- 0.2 mEq/L. These results suggest that unlike hemodialysis, which is not associated with short-term changes in red-cell electrolytes, intermittent peritoneal dialysis results in a reversible increase in erythrocyte sodium. This change appears to be causally related to the decrease in extracellular potassium concentration.