Regulation of the NaK-ATPase of sheep red blood cells of the low- K+ genotype

A genetic polymorphism of sheep red cells characterized by differences in the intracellular K$ sp+$ concentration of their mature red cells reflects differences in their Na/K pump activity as well as pump kinetics. This polymorphism is linked to the ML blood group system, as follows. Homozygous high-K$ sp+$ (HK) cells possess only M antigen, whereas homozygous low-K$ sp+$ (LK) cells have an antigen, L$ rm sb{p},$ which is an endogenous inhibitor of the Na/K pump since isoimmune antiserum, anti-L$ rm sb{p},$ stimulates the Na/K pump of LK cells by relieving this inhibition. In this study, it is shown that the $ rm L sb{p}$ antigen is a molecular entity distinct from the pump. Thus, anti-$ rm L sb{p}$ stimulated the activity (ouabain-sensitive $ rm sp{86}Rb sp+(K sp+)$ influx) of exogenous rat kidney pumps incorporated by fusion of kidney microsomes into immature LK red cells. Moreover, the $ rm L sb{p}$ antigen is responsible for the changes in pump kinetics associated with maturation of LK sheep red cells. The evidence is that treatment of immature LK cells with either anti-L$ rm sb{p}$ or trypsin (which cleaves the $ rm L sb{p}$ antigen) prevents the maturation-associated change in kinetics of the pumps, normally from one of no inhibition (immature cells) to that of marked inhibition by intracellular K$ sp+$ (mature cells). In addition, it was shown that kidney pumps delivered into immature LK red cells develop sensitivity to inhibition by intracellular K$ sp+$ following maturation of the cells in vitro. Mature LK cells have fewer pumps than mature HK cells and, therefore, another question addressed was whether the $ rm L sb{p}$ antigen promotes the greater loss of pumps in LK red cells during maturation. It was observed that modification of the $ rm L sb{p}$ antigen of immature LK cells with either anti-L$ rm sb{p}$ or trypsin diminished the subsequent loss of pumps during maturation in vitro. It was shown also that there is little decline in the number of $ r