The role of the cellular sodium pump in human granulopoiesis in vitro

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Abstract
The specific Na pump antagonist ouabain was used to study the effect of Na pump inhibition on granulopoietic colony formation by normal human bone marrow cells cultured in soft agar for 7 days. Suppression of colony formation was dose-dependent and occurred at a low and reproducible concentration. The use of an extended range of concentration (1 .times. 10-19-1 .times. 10-4 M) revealed no additional effect. Inhibition occurred when colony formation was stimulated by either normal human white blood cells in a soft agar underlayer or the inclusion of preformed colony-stimulating activity. Sensitivity to inhibition was similar under either set of conditions, the 50% inhibitory concentrations being 2.70 .+-. 0.43 (SE) .times. 10-8 M and 2.83 .+-. 0.21 .times. 10-8 M, respectively. This was interpreted as showing an effect primarily on the colony-forming cells rather than on the cellular production of colony-stimulating activity. Inhibition of colony formation by ouabain was opposed by the addition of extra K to the culture medium, confirming that the inhibition was mediated via a perturbation of monovalent cation exchange. Inhibition by 2 .times. 10-7 M ouabain appeared to be reversible by simple washing after exposure for up to 24 h, suggesting that the inhibitory effect of ouabain is not primarily cytotoxic.