Erythropoiesis in vitro. IV. Effects of ouabain on erythroid stem cells (CFU-e and BFU-e)

Recent investigations employing various ionophores and cardiac glycosides have detected an increase in the number of late-stage erythroid progenitor cells (CFU-e) cultured from normal murine marrow. We report that the cardiac glycoside, ouabain, not only increased the number of erythroid progenitor cells, but also elevated the number of the earliest erythroid colony-forming cells (BFU-e). This rise in the number of erythroid stem cells was dose dependent with a maximum increase in erythroid colony numbers observed at 10(-15) M ouabain. Furthermore, ouabain exerted its stimulatory activity by increasing the proportion of erythroid colony-forming cells (BFU-e) in cell cycle as determined by 'thymidine suicide' experiments. The substitution of dialyzed fetal calf serum in the culture medium markedly inhibited the erythroid colony stimulation by ouabain. The deficient factor in dialyzed fetal calf serum appears to be K+, because the stimulatory influence of ouabain was restored upon reconstitution of the serum with K+. These studies suggest that ouabain-induced erythropoietic enhancement may involve mechanisms other than inhibition of membrane-bound Na+/K+ATPase.