Red cell ouabain binding sites, Na +K +-ATPase, and intracellular Na + as individual characteristics

Abstract

Red cells were used as model cells to assess the relationship between the number of ouabain binding sites and the Na +K +-ATPase activity in humans. ( 3H) ouabain binding to intact red cells was found to be a reversible reaction and rectilinear Scatchard plots were obtained. Interindividual comparison revealed identical slopes, whereas the abscissa intercepts differed, indicating variations in the number of ouabain binding sites. The number of sites ranged from 330 to 890 ( x = 453 ± 104 SD ) per red cell in 73 individuals and was intraindividually stable during the course of 3–12 months. The number of sites was significantly lower in the middle-age females compared to younger ones. A linear relationship (r=0.96) was found between the total number of ouabain binding sites of intact red cells and the Na +K +-ATPase activity of red cell ghosts. The catalytic activity varied little among individuals; a turnover number of 5500 ± 250 (SD) molecules ATP hydrolyzed per site and per min was calculated. A highly significant correlation was established between [Na +] i of red cells in vivo and the number of ouabain binding sites.