Functional and structural properties of Na+/K+-ATPase enzyme in neonatal erythrocytes

Background The Na+/K+-pump is the main regulator enzyme of intracellular monovalent cation concentration. There are only limited data available concerning its structure and function in healthy neonates, in comparison with data available regarding its structure and function in children. Patients and methods Samples of 100 mu L of anticoagulated blood were taken from 53 healthy neonates (age under 6th postnatal day, median age 3.5 days) and 61 healthy children (median age 12.4 months, range 6-36 months,). The Na+/K+-ATPase activity, its sensitivity to ouabain (a digoxin-analogue substance) and the expression of Na+/K+-ATPase subunit isoforms were determined. Results The enzyme activity (429.2 +/- 17.1 versus 295.5 +/- 10.2 U, P < 0.001) and I-50 value for ouabain inhibition (1.50 +/- 0.10 versus 0.96 +/- 0.10 mu mol L-1, P < 0.05) was higher in neonates. More alpha(1) subunits (relative density: 1.16 +/- 0.10 versus 0.75 +/- 0.03, P < 0.001) and higher alpha(1)/alpha(2) ratio (4.14 +/- 0.21 Versus 2.02 +/- 0.16, P < 0.01) were detected. Conclusion This is the first study demonstrating changes of Na+/K+-ATPase molecules not only in enzyme activity, but also on protein level. Our results might contribute to the understanding of the resistance of neonatal cell membranes toward the pharmacodynamic actions of cardiac glycosides.