Fig. 2.

Respiratory capacity of mitochondrial subpopulations in WT and db/db hearts. A–G: state 3 and state 4 respiration rates with glutamate + malate (A and B), palmitoylcarnitine (C and D), electron transport chain (ETC) complex activities (E and F), and ATP synthase activity (G) were assessed in isolated mitochondrial subpopulations [SSM (A, C, and E) and IFM (B, D, and F)] from hearts of 18-wk-old WT and db/db mice. State 3 and state 4 respiration rates were determined in the presence of the substrates glutamate + malate as well as palmitoylcarnitine, and state 3 respiration was examined upon the addition of ADP. ETC complex I, III, and IV activities were assessed spectrophotometrically by measuring the oxidation of NADH (complex I), reduction of cytochrome c (complex III), and oxidation of cytochrome c (complex IV). Respiration rates are expressed in nmol·min⁻¹·mg protein⁻¹, whereas enzymatic activities are expressed in activity·min⁻¹·mg protein⁻¹. Values are means ± SE; n = 6 for each group. *P < 0.05 for WT vs. db/db.