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

Activation and proliferation signals in murine macrophages: stimulation of Na+,K+-ATPase activity by hemopoietic growth factors and other agents

Purified colony stimulating factor (CSF-1) stimulates the Na+,K+-ATPase activity of murine bone marrow-derived macrophages (BMM) and resident peritoneal macrophages (RPM) measured as ouabain-sensitive 86Rb+ uptake. Similar concentrations of CSF-1 stimulate the Na+,K+-ATPase activity and DNA synthesis in BMM whilst ouabain, a specific inhibitor of the Na+,K+-ATPase, also inhibits this CSF-1-mediated DNA synthesis. Other purified hemopoietic growth factors, granulocyte-macrophage CSF (GM-CSF) and interleukin-3 (IL-3), and the tumor promoter, 12-O-tetradecanoyl-phorbol-13-acetate (TPA), even though differing in their mitogenic capabilities, are also stimulators of the Na+,K+-ATPase activity in BMM and RPM. The non-mitogenic agents, lipopolysaccharide (LPS) and Concanavalin A (Con A), are also active. CSF-1 stimulation of the Na+,K+-ATPase was shown to be dependent on elevation of intracellular Na+ via an amiloride sensitive Na+-channel, most likely representing Na+/H+ exchange activity. Such stimulation of Na+,K+-ATPase activity via activation of the Na+/H+ exchange appears to be a necessary but insufficient early macrophage response for subsequent DNA synthesis.

Inhibition of normal human granulopoiesis in vitro by amiloride: evidence for the involvement of facilitated sodium influx in the induction of differentiation

The formation of colonies by normal human bone marrow granulopoietic progenitor cells in vitro in soft agar was inhibited in a simple, dose-dependent manner by amiloride (50% inhibitory concentration 26.4 +/- 3.4 microM, n = 9). Such inhibition was reversible and is evidence for the involvement of amiloride-sensitive sodium influx in granulopoietic cell proliferation. Colony-forming cells were capable of some proliferation at concentrations of amiloride 3-fold in excess of that required to inhibit full colony formation. A two-stage model is invoked to explain this observation: an early amiloride-insensitive stage and a late amiloride-sensitive stage which includes terminal differentiation. We conclude that the cellular mechanism by which differentiation is induced includes activation of the amiloride-sensitive sodium influx channel, which would indicate a new approach to the therapeutic induction of differentiation in vivo.

Lithium stimulation of in vitro granulopoiesis: evidence for mediation via sodium transport pathways

Lithium (Li) stimulates granulopoiesis both in vitro and in vivo by increasing the number of committed granulocyte-macrophage colony forming stem cells (CFU-GM) either through direct or indirect mechanisms. In this report are described further studies designed to investigate if this Li stimulation could be altered by modulating Li transport using agents known to influence monovalent cation transport. Ouabain, a Na/K ATPase inhibitor, added to non-adherent bone marrow cells either before or immediately after the addition of ultra-pure Li (1 mEq) produced an irreversible reduction in CFU-GM indicating the importance of the Na/K ATPase in these processes. Further studies using the sodium and potassium ionophores gramicidin and valinomycin (5 micrograms/ml) followed by a delay in the addition of Li (0, 5, 15, 20, 30, 60 and 120 min) reduced CFU-GM; however, this reduction was less severe in the presence of gramicidin, indicating sodium transport pathways may be required for Li action. To further explore this hypothesis, studies were performed using the more specific sodium transport inhibitors, amiloride and phloretin. Both were effective in reducing the ability of Li to increase CFU-GM. Studies incorporating the calcium ionophore, A23187, demonstrated that in the presence of Li, a further reduction in CFU-GM was observed indicating that Li was unable to reverse this A23187 induced reduction in CFU-GM. These data suggest that in the presence of active calcium transport, the ability of Li to increase CFU-GM is restricted.

CSF-1 stimulates Na+K+-ATPase mediated 86Rb+ uptake in mouse bone marrow-derived macrophages

86Rb+ was used as an isotopic tracer for the measurement of K+-uptake into quiescent murine bone marrow-derived macrophages. 86Rb+ uptake was inhibited by ouabain indicating a Na+K+-ATPase is being measured. In support of this finding, increased sensitivity to ouabain inhibition was seen when the K+ content of the medium was reduced. A purified colony stimulating factor (CSF-1) was shown to stimulate the ouabain-sensitive 86Rb+ uptake in a dose-dependent manner. Such colony stimulating factor stimulation of 86Rb+ (K+) influx was rapid, with a maximal effect seen 10 minutes after growth factor addition followed by a gradual decrease. Thus increased Na+K+-ATPase activity was an early response of macrophages to the colony stimulating factor.

[3H]Ouabain binding and 86 rubidium uptake during the dimethyl sulfoxide-induced differentiation of human promyelocytic leukemia HL-60 cells

When HL-60 cells were induced to differentiate into granulocyte-like cells by culture in the presence of 1.3% dimethyl sulfoxide, an increase in the rate of ouabain-sensitive 86Rb transport was observed during the first 6 h followed by a constant decrease which became stable on day 4 at about 40% of control level. By contrast, the number of ouabain binding sites remained constant during the first 24 h then decreased with the same kinetics as that of the 86Rb transport rate. These results suggest that alterations in ionic fluxes, through activation of the sodium pump, are part of the early events resulting in HL-60 cell differentiation.