Ginsenoside Rb1 selectively inhibits the activity of mitochondrial complex I but not complexes II and IV. A, Oxygen consumption rate (OCR, % baseline) of H9c2 cells in the presence of ginsenoside Rb1 (10 µM), FCCP (2.5 µM), pyruvate (Pyr, 10 mM), and antimycin A (AA, 1 µM). B, OCR traces of H9c2 cells permeabilized by digitonin (3 µg/mL) and then stimulated by ADP (1 mM), pyruvate (5 mM), malate (5 mM) and Rb1 (10 µM). C, Mitochondrial complex I activity in H9c2 cells treated with ginsenoside Rb1 (10 µM) or rotenone (1 µM). D, OCR traces of permeabilized H9c2 cells exposed to ADP (1 mM), glutamate (5 mM) plus malate (5 mM), and succinate (5 mM). Here, H9c2 cells were pretreated with ginsenoside Rb1 (10 µM) or rotenone (1 µM) for 1 h prior to OCR measurements. Then ginsenoside Rb1 or rotenone was then either left on for further assay, or washed out with replacement of drug-free assay buffer. E, OCR (% baseline) of permeabilized H9c2 cells in the presence of succinate (5 mM), rotenone (0.5 µM), and ginsenoside Rb1 (10 µM). F, OCR (% baseline) of H9c2 cells injected with FCCP (2.5 µM), TMPO (0.4 mM) plus ascorbate (0.4 mM), ginsenoside Rb1 (10 µM), and azide (5 mM). Data were expressed as mean ± SD. *p < 0.05: vs. untreated control. AA, antimycin A; Dig, digitonin; FCCP, carbonyl cyanide p-trifluoromethoxyphenylhydrazone; G, glutamate; M, malate; Pyr or P, pyruvate; Rb1, ginsenoside Rb1; Rot or R, rotenone; S, succinate; TMPD, tetramethyl-p-phenylene diamine.