DECLINE IN NUMBER OF NA-K PUMPS ON LOW-K+ SHEEP RETICULOCYTES DURING MATURATION IS MODULATED BY L(P) ANTIGEN

The number of the Na-K pumps on sheep red blood cells declines markedl y during cell maturation. In addition, in red blood cells of the low-K + (LK) phenotype, there is an increase during maturation in the affini ty of the pumps for intracellular K+. This increase does not occur in cells of the high-K+ (HK) phenotype. This HK/LK polymorphism is associ ated with the MIL blood group antigen system. The L, antigen, which is on only LK cells, promotes the increase in affinity for K+ [Am. J. Ph ysiol. 265 (Cell Physiol. 34): C99-C105, 1993]. Mature LK cells have f ewer pumps than mature HK cells. The present study shows that the L(p) antigen also promotes the loss of pumps in LK cells. The evidence was that modification of the L(p) antigen of immature LK red blood cells either with anti-L(p), antibody or by trypsinization diminished the lo ss of pumps during culture in vitro (numbers determined from [H-3]ouab ain binding). Confirmation came from demonstration of the decline duri ng maturation of the amount of the a-subunit of the Na-K pump (measure d by immunoblotting), which was also retarded by pretreatment with ant i-L(p), or trypsin. Comparisons of the relative amounts of L(p) antige n on immature and mature LK cells showed that there is little decline in number of antigens during maturation. Therefore there is an increas e in the antigen-to-pump ratio during maturation even though an associ ation between pumps and antigens is necessary for the loss of pumps.