Decline in number of Na-K pumps on low-K+ sheep reticulocytes during maturation is modulated by Lp antigen.

The number of the Na-K pumps on sheep red blood cells declines markedly during cell maturation. In addition, in red blood cells of the low-K+ (LK) phenotype, there is an increase during maturation in the affinity of the pumps for intracellular K+. This increase does not occur in cells of the high-K+ (HK) phenotype. This HK/LK polymorphism is associated with the M/L blood group antigen system. The Lp antigen, which is on only LK cells, promotes the increase in affinity for K+ [Am. J. Physiol. 265 (Cell Physiol. 34): C99-C105, 1993]. Mature LK cells have fewer pumps than mature HK cells. The present study shows that the Lp antigen also promotes the loss of pumps in LK cells. The evidence was that modification of the Lp antigen of immature LK red blood cells either with anti-Lp antibody or by trypsinization diminished the loss of pumps during culture in vitro (numbers determined from [3H]ouabain binding). Confirmation came from demonstration of the decline during maturation of the amount of the alpha-subunit of the Na-K pump (measured by immunoblotting), which was also retarded by pretreatment with anti-Lp or trypsin. Comparisons of the relative amounts of Lp antigen on immature and mature LK cells showed that there is little decline in number of antigens during maturation. Therefore there is an increase in the antigen-to-pump ratio during maturation even though an association between pumps and antigens is necessary for the loss of pumps.