Influence of ouabain on cell inactivation by irradiation.

Background: It has been suggested that irradiation affects the function of the Na(+)-K(+)-ATPase. Here we examine the influence of the inhibitor ouabain on the cytotoxicity of irradiation.

Material And Methods: Cell colony assay, cell survival, 86Rb-uptake, flow cytometry.

Results: In V79, HeLa and A549 cells ouabain alone causes a significant growth reduction at medium concentrations of 10(-4) M, 10(-6) M and 10(-7) M, respectively. When cells were exposed to the drug for 1 h and subsequently irradiated, the SF2 values decreased from 0.55 to 0.41, from 0.42 to 0.18 and from 0.57 to 0.35 in V79, HeLa and A549 cells, respectively. These effects were manifest at drug concentrations of 10(-3) M, 10(-6) M and 10(-7) M respectively, where Na(+)-K(+)-ATPase activity as measured by 86Rb-uptake was reduced to 40 to 60% of the control value. Addition of the drug after irradiation and when the G2/M cell cycle block was firmly established, markedly delayed the recovery of cells for well over 6 h and G1 levels remained at 50% of the control values.

Conclusion: It is concluded that ouabain is strongly dose modifying in the human cell lines HeLa and A549 at concentrations which correlate with the inhibition of the Na(+)-K(+)-ATPase. Ouabain also inhibits the recovery of cells blocked in the cell cycle by irradiation.