Functional and metabolic studies on red blood cell sodium transport in chronic uremia

Red blood cells from 7 out of 13 patients with chronic uremia were found to have increased intracellular concentrations of sodium associated with a reversible inhibition of ouabain-sensitive Na efflux when incubated in control plasma. Although mean Na-K-ATPase activity of RBC hemolysates was only moderately decreased (21.8 +/- 1.5 vs. 26.5 +/- 1.8 nmol Pi/mg protein/h), enzyme kinetics revealed a significant increase in KmATP values for this enzyme in uremic RBCs (1.01 +/- 0.1 vs. 0.58 +/- 0.03; p less than 0.001) which was closely correlated to serum creatinine concentration (r = 0.9034). While aerobic glycolysis was unaltered, an increase in glucose-6-phosphate dehydrogenase activity was observed, i.e. the enzyme initiating the pentose-phosphate cycle. In addition, intracellular ATP concentrations of uremic RBCs were significantly higher than ATP concentrations of control RBCs (2.13 +/- 0.22 vs. 1.32 +/- 0.06 mmol/l RBC; p less than 0.01). These data suggest that high intracellular concentrations of Na and ATP in uremic RBCs partially result from a competitive reversible inhibition of the transport ATPase by uremic toxins.