Fig. 1.

In vivo H₂S levels and H₂S-induced inhibition of mitochondrial respiration. (A and B) H₂S levels in plasma and liver of summer and winter hibernating squirrels (interbout euthermia [IBE] and torpor). Individual values are shown with mean ± SEM. Different letters (a–b) indicate a significant difference, P < 0.05. (C–E) Representative traces of respiration rate of liver mitochondria isolated during summer, IBE and torpor. Arrows indicate additions of 2.5 μM rotenone (R), 6 mM succinate (S) and H₂S (added as Na₂S). Mitochondria (10–30 μl, ~200 μg protein) were transferred to the respiration chamber containing 2 ml of mitochondrial respiration medium (0.5 mM EGTA, 3 mM MgCl₂, 60 mM l-lactobionate, 20 mM taurine, 10 mM KH₂PO₄, 20 mM HEPES, 110 mM sucrose, 1 g/l fatty acid-free BSA, pH 7.1) at 37 °C and constant stirring (750 rpm). Electrodes were calibrated daily to 0% oxygen (using a yeast suspension) and air-saturation. Respiration rates were expressed relative to protein concentration determined using a protein assay dye (Bio-Rad). (F) Relative respiration rate (minimum rate after Na₂S addition normalized to initial respiration rate) plotted as a function of added Na₂S. Data are shown as mean ± SD, N = 7 (summer) and N = 2 (IBE and torpor).