Subtoxic concentrations of Mn do not affect metabolic balance. A, Relative caspase-3/7 activity following 24-h Mn exposure. Left, STHdh^Q7/Q7; Right, STHdh^Q111/Q111. Results combined from 3 independent experiments, n = 4–6; total n = 16 (see Materials and Methods section). B, ADP/ATP ratio following 24-h Mn exposure. Left, STHdh^Q7/Q7; Right, STHdh^Q111/Q111. Results combined from 3 independent experiments, n = 3–4; total n = 6–10. C, Relative quantity NAD+, NADH, and NADH/NAD+ ratio following 24-h Mn exposure. Top, STHdh^Q7/Q7; Bottom, STHdh^Q111/Q111. Results combined from 3 independent experiments, n = 3; total n = 9. Mn concentration (µM) is indicated below respective bars. Concentrations in red reflect concentrations above which significant cytotoxicity is observed. Error bars reflect SEM. **p < .01, ***p < .001, by Dunnett’s test relative to control.