INFLUENCE OF SODIUM SELENITE ON THE VIABILITY AND INTRACELLULAR SYNTHETIC ACTIVITY (DNA, RNA, AND PROTEIN-SYNTHESIS) OF HELA-S3 CELLS

HeLa S3 cells were incubated with varied concentrations of Na2SeO3 for varying periods of time and assayed for their viability (trypan blue dye exclusion test), intracellular metabolic activity (incorporation of 3H-labeled precursors into DNA, RNA, and protein), and selenite content (isotope dilution analysis using 75Se-labeled Na2SeO3). The metabolic activities decrease exponentially with time at a given toxicant concentration in the medium while, at a given time period of intoxication, they cease in an abrupt fashion when plotted, for instance, against the logarithm of the toxicant concentration in the medium. The amount of Na2SeO3 bound by the cells increases with time; a leveling off, however, is noted between 6 and 12 hr of incubation. A Na2SeO3 level of about 20 × 10-18 mol/cell, which can also be expressed as 6.63 μm intracellular selenite concentration or as 0.5 ppm of selenium per cell, appears to represent the threshold below which acute toxic effects are not experienced by HeLa S3 cells, at least not at incubation periods up to 36 hr. Macromolecular synthetic activity becomes inhibited at selenium levels in the cells above 0.5 ppm. DNA synthesis, for instance, proceeds with 40% activity of the control at 72.7 × 10-18 mol selenite/cell or at about 2 ppm of selenium in the cells. Recovery from intoxication appears to be possible for cells even at selenite levels up to 3 × 10-15 mol/cell (about 130 ppm) although only after lag periods exceeding three or four generation times. Surprisingly high selenite concentrations in the medium (above 1 mm) are needed before the outer plasma membrane of the cells becomes permeable to trypan blue. The toxic levels of selenite found in this study are compared with some of the LD50 data available from the literature. A good agreement is noted. © 1979.