Figure 7

Influence of the initial oxygen level in the wells before exposure starts \(\left. {{\varvec{c}}_{O2}^{cell} } \right|_{init}\) on the cellular response. (A) Time courses of the oxygen concentration in the wells of the reactor, which are filled with different cell numbers of HepG2 hepatocytes, during exposure to 12.5 mM acetaminophen (period of exposure is indicated by grey background colour). Varying cell numbers in the wells result in different initial oxygen concentrations. In (B) the magnitude of the fast cellular response (|1|) is plotted as a function of the initial oxygen level in the wells just before exposure starts \(\left. {{\varvec{c}}_{O2}^{cell} } \right|_{init}\) for various concentrations of acetaminophen. The initial oxygen levels \(\left. {{\varvec{c}}_{O2}^{cell} } \right|_{init}\) were adjusted by the number of cells N introduced to a particular well. Cell numbers N that correspond to an oxygen concentration close to 0% were 3 × 10⁵ cells whereas for obtaining an oxygen concentration of 80% only 5 × 10⁴ cells were introduced to one well. For initial oxygen levels \(\left. {{\varvec{c}}_{O2}^{cell} } \right|_{init}\) between 0 and approximately 40% the magnitude of the fast cellular response is constant for a given acetaminophen concentration, for higher initial oxygen levels the magnitudes steadily decrease for increasing initial oxygen levels \(\left. {{\varvec{c}}_{O2}^{cell} } \right|_{init}\).