ERYTHROCYTE SODIUM-POTASSIUM TRANSPORT IN HYPERKALEMIC AND NORMOKALEMIC INFANTS

One of the causes of early onset hyperkalaemia in very low birth weight infants is presumed to be the dysfunction of K+ transport across the cell membrane. Sodium-potassium adenosine triphosphatase(Na+-K+ ATPase) is known to play a major role in K+ transport. We compared the concentrations of erythrocyte Na+-K+ ATPase (V-max levels) for hyperkalaemic and normokalaemic infants of matched gestational age. In hyperkalaemic infants, the highest levels of V-max were reached at 24-48 h after birth, but in normokalaemic infants, there were no significant changes in V-max levels during the Ist week after birth. At 12-72 h after birth, erythrocyte K+ concentrations for hyperkalaemic infants were higher than those of normokalaemic infants. For both groups of infants, the highest levels of plasma K+ during the 1st week after birth showed a positive correlation with those of V-max. Conclusion Na+-K+ ATPase on the cell membrane is activated to compensate for hyperkalaemia; however, when this compensation is incomplete, hyperkalaemia occurs.