Dose specified as mol cell^-1 more accurately reports toxicity of 1,4-BQ in cell culture experiments than initial concentration in medium.

<p><b>(A)</b> These data show two different physical setups for the experiments, black circle (1.7 x 10⁶ cells) and gray diamond (3.3 x 10⁶ cells). Clonogenic survival of MIA PaCa-2 cells was measured in triplicate after a 4-h exposure to 16.7 μM 1,4-BQ in different volumes of medium, yielding a range of doses on a mol per cell basis. No dose dependence is observed when the dose 1,4-BQ is expressed as the initial concentration in the culture medium. Error bars represent the standard deviation of the median of triplicate measures. <b>(B)</b> The data of panel <b>A</b> are transformed to express the dose of 1,4-BQ in units of fmol cell^-1. A far better delineation of the dose-dependent toxicity is observed in each of the two sets of experiments. Error bars represent the standard deviation of the median of triplicate measures. <b>(C)</b> Using a varying number of MDA-MB231 cells, clonogenic survival varied considerably after a 4-h exposure to 16.7 μM 1,4-BQ in 10.0 mL of medium in T-25 culture flasks (each point has <i>n</i> = 2 for biological replicates, <i>n</i> = 3 within each replicate). Error bars represent the standard deviation of the mean. <b>(D)</b> As with MIA PaCa-2 cells, when the dose of 1,4-BQ is expressed in units of fmol cell^-1, a much more informative delineation of the dose-dependent toxicity in MDA-MB231 cells is observed. Error bars represent the standard deviation of the mean. (<b>E</b>) Using a varying number of MIA PaCa-2 cells, intracellular ATP concentration of MIA PaCa-2 cells varied considerably after a 4-h exposure to 8.35 μM 1,4-BQ in 5.0 mL of medium in T-25 culture flasks (each point has a <i>n</i> = 2 for biological replicates, <i>n</i> = 2 within each replicate). Error bars represent the standard deviation of the mean; many standard deviations are smaller than the symbol. <b>(F)</b> When the dose of 1,4-BQ is expressed in units of fmol cell^-1, a much more informative delineation of the dose-dependent effect on intracellular ATP concentration in MIA PaCa-2 cells is observed. Error bars represent the standard deviation of the mean.