RED CELL STROMAL ADENOSINE TRIPHOSPHATASE (ATPASE) OF NEWBORN INFANTS

Extract:Erythrocytes of the newborn infant are known to lose potassium at a rapid rate during short periods of incubation. Net potassium loss can occur as a consequence of either increased leak or inadequate active influx in the presence of normal leak. This inadequate active influx may be associated with peculiarities in the properties of the cation transport process situated in the erythrocyte membrane. For this reason, red cell stromal ATPase, a membrane enzyme intimately involved in cation transport, was examined in the erythrocytes of fourteen normal adults, sixteen term infants, ten premature infants, and thirteen patients with reticulocytosis. Km ATP was found to be similar in all groups except in premature infants, in whom it was slightly higher than it was in adults. The range of values was 0.29 to 0.36 mM. The concentration of sodium or potassium required to produce half-maximal activation of the stromal ATPase was the same in the four groups, 9.4 to 10.0 mM for sodium and 0.82 to 1.10 mM for potassium. Reticulocytes were found to possess increased ATPase activity, but term infants with comparable reticulocyte counts showed the same total ATPase activity as normal adults. Both term and premature infants were found to possess significantly less ouabain-sensitive membrane ATPase and thus less of the sodium-potassium activated membrane transport system than other cells of comparable reticulocyte count. Ouabain (10-4 M) produced a 60.1 ± 4.8% inhibition of ATPase activity in adults and a 56.2 ± 8.9 % inhibition in subjects with reticulocytosis. In contrast, ouabain produced an inhibition of only 43.1±6.4% in term infants and 39.3±6.3% in premature infants. These findings suggest that neonate erythrocytes have a relative deficiency of membrane ATPase that is activated by sodium and potassium. Speculation:That the erythrocytes of the newborn infant have less sodium-potassium activated stromal ATPase may be responsible for the increased potassium leak observed when these cells are incubated for short periods at 37°. This relative ATPase deficiency is another illustration that the erythrocytes of the newborn are metabolically different from those of normal adults, and this particular difference may play a central role in the shortened survival of the red cells of the newborn infant. Investigation of other neonatal tissues is warranted to obtain evidence of a generalized difference in cation transport during this period of life. © International Pediatrics Research Foundation, Inc. 1969. All Rights Reserved.