Objective: To study the developmental changes in RBC Na+,K+-ATPase (NaK) α and β subunit isoform abundance, NaK activity and NaK cation-pump function in preterm and term neonates. Study Design: RBC NaK subunit isoform abundance was determined by Western blot analysis from pooled blood samples. NaK activity was measured in purified RBC membrane (PRBCM) and detergent pretreated RBC (DPRBC) preparations using a total of 350 μL of whole blood. In the PRBCM preparation, NaK activity is measured in the absence of endogenous regulators of enzyme activity, while in the DPRBC preparation these regulators are present. RBC NaK cation-pump function was assessed by the measurement of intracellular sodium ([Na+]ic) and potassium ([K+]ic) concentrations. Blood samples were obtained from 56 preterm neonates with 28-32 weeks gestation (Group 1), 58 preterm neonates with 33-36 weeks gestation (Group 2) and 122 term neonates (Group 3) during the 2 postnatal days. Results: α1 subunit isoform abundance was higher by 76%* and 32%*, while β2 isoform abundance was lower by 49%* and 13% in Groups 1 and 2, respectively compared to Group 3 (* = P<0.05, ANOVA). α2 and β1 isoform abundance did not change with maturation. PRBCM NaK activity was 624 ±337*, 481 ±195* and 404 ±167* nmol ATP/mg protein/h in Groups 1,2 and 3, respectively (* = P<0.05 between the groups, ANOVA). DPRBC NaK activity was 2010 ±716*, 2560 ±710 and 2595 ±842 nmol P/mL RBC/h in Groups 1,2 and 3, respectively (* = P<0.05 in Group 1 vs. Group 2 and 3, ANOVA). [Na+]ic and ([K+]ic did not change with maturation. Conclusion: RBC α1 and β2 NaK subunit isoform expression is developmentally regulated. The increased abundance of α1 subunit isoforms results in an increased PRBCM NaK activity in the more immature neonate. However, in the DPRBC preparation, RBC NaK activity of immature neonates is decreased. We speculate that this finding could be explained by the observation that the levels of endogenous NaK inhibitors are highest in immature neonates. If [Na+]ic and [K+]ic are indeed appropriate measures of NaK cation pump function, then RBC NaK cation pump function remains unchanged despite the developmentally regulated changes in NaK subunit expression and ATPase activity.
|Journal||Journal of Investigative Medicine|
|Publication status||Published - Feb 1999|
ASJC Scopus subject areas
- Biochemistry, Genetics and Molecular Biology(all)