Kinetic characteristics of bicarbonate-chloride exchange across the neonatal human red cell membrane

Abstract

The kinetics of HCO 3 −/Cl − exchange across red cell membrane of newborn infants was studied using a stopped-flow rapid reaction apparatus with a glass pH electrode attached. The measured apparent permeability P is (1.35±0.08 (S.E.)) · 10 −4 cm/s ( n=30) for newborns, compared with (3.1 ± 0.4) · 10 −4 cm/s ( n=15) for adults. These correspond to half-times of 0.2 s for newborns and 0.1 s for adults indicating that neonatal red cells exchange Cl − for HCO 3 − only half as fast as do adult cells. The temperature dependence of the exchange rate was studied from 2 to 42°C. From the Arrhenius plot the activation energy of the exchange process in neonatal red cells changes from 22.9 kcal/mol (low temperature) to 4.8 kcal/mol (physiological temperature) at a transition temperature of 17°C. These values are lower than the corresponding values for adult red cells, 34.7 and 10.2 kcal/mol. HCO 3 −/Cl − exchanges in both adult and neonatal red cells are inhibited by phlorizin. Inhibition constants K i are 0.8 mM and 2.5 mM for adults and newborns, respectively. The differences in the values of the HCO 3 −/Cl − exchange rate constant and the activation energy of the exchange process between neonatal and adult red cells indicate that there is a modification of HCO 3 −/Cl − transport system in the neonatal red cell membranes.