Erythrocyte sodium-potassium transport in cystic fibrosis

Erythrocytes from 15 patients with cystic fibrosis (CF) aged 8 mo to 22 y (mean age 12.8 y) were analyzed for Na+,K(+)-ATPase activity and sodium, potassium, and ATP concentrations. Sodium concentrations and Na(+)-K+ ratio of erythrocytes were statistically significantly lower in the CF patients [6.6 (SD 1.9) versus 9.2 (SD 1.1) mmol/L (p less than 0.01) and 0.070 (SD 0.023) versus 0.104 (SD 0.016) mmol/L (p less than 0.01), respectively]. The Na+,K(+)-ATPase activity was similar compared with that of reference individuals [536 (SD 100) versus 488 (SD 92) nmol inorganic phosphate/mg protein/h]. Intraerythrocyte sodium concentration and Na(+)-K+ ratio were thus lower in relation to the recorded Na+,K(+)-ATPase activities in controls, indicating a change of the passive transmembrane movements of sodium ions in CF. There was a rise of erythrocyte sodium and Na(+)-K+ ratio despite unchanged Na+,K(+)-ATPase activity after regular infusion of a fat emulsion rich in essential fatty acids, inferring that an altered membrane composition by essential fatty acid deficiency could explain the low intracellular sodium concentration in CF.