ALTERED ERYTHROCYTE SODIUM-LITHIUM COUNTERTRANSPORT AND NA+ K+-ATPASEACTIVITY IN CYSTIC-FIBROSIS/

Patients with cystic fibrosis (CF) exhibit normal concentrations of so dium and chloride in spite of the disturbance of Cl- and Na+ transport in epithelial cells. To characterize compensatory mechanisms in the r egulation of sodium homeostasis, erythrocytes of 13 CF patients were a nalysed for sodium-lithium counter-transport (SLC), Na+/K+-ATPase acti vity and intracellular sodium content. Values were compared to those o f healthy controls. Patients with CF had normal serum sodium and chlor ide concentrations and renal excretions of these ions were within the physiological range. Intracellular sodium concentration was similar in the CF and the control group (6.8 +/- 2.2 vs 5.7 +/- 1.0 mmol/l RBCs) . Red blood cells' SLC and Na+/K+-ATPase activity were elevated in CF patients (381 +/- 106 mu mol/h/l RBCs vs 281 +/- 64; p < 0.01) and (44 5 +/- 129 mu mol ATP mg prot/h vs 322 +/- 84, p < 0.01). Our study dem onstrates that transmembrane cation transport systems are highly activ ated in CF. The increased sodium transport may be part of a compensato ry mechanism of sodium homeostasis in children with CF.