Comparison of the Digitalis Receptor in Erythrocytes from Preterm Infants and Adults

ABSTRACT: We compared 86rubidium by erythrocytes of preterm infants and adults as a measurement of their Na+, K+, ATPase enzyme system. In neonates, total uptake (0.92 ± 0.13 μg/106 cells) and specific uptake (0.64 ± 0.076 μg/106 cells) were significantly higher than in adults (0.52 ± 0.1 and 0.29 ± 0.06 μg/106 cells, respectively; p < 0.025). The percentage of specific uptake from total uptake was higher in infants (73.3 ± 2.3%) than in adults (57.9 ± 4.6%) (p < 0.005). No differences were found in the affinity constant of 86Rb uptake between infants (4.35 ± 0.48 ng/ml) and adults (4.85 ± 0.48 ng/ml). Stratification of infants according to their serum K+ concentrations revealed that levels above 5.4 mEq/liter were associated with a higher specific uptake (0.79 ± 0.107 μg/106 cells) than in normokalemic infants (0.54 ± 0.09 μg/106 cells) or adults (0.304 ± 0.061 μg/106 cells) (p < 0.05). The difference between hyperkalemic and normokalemic infants persisted after excluding those who received adult packed cells (0.88 ± 0.1 and 0.6 ± 0.12 μg/106 cells, respectively) (p < 0.05). Infants with serum K+ > 5.8 mEq/liter received on average signiflcantly more K+ in previous days (2.46 ± 0.49 versus 1.13 + 0.34 mEq/kgday; p < 0.025). The different K+ level could not be attributed to different creatinine clearance in the two groups.