Figure 3.

A) In vitro measurement of oxygen flux in isolated skeletal muscle mitochondria of WT and NaPi2a^−/− mice increased in a dose-dependent manner upon addition of 1 and 5 mM Pi to medium; however, mitochondrial function per se is not impaired in NaPi2a^−/− mice compared with WT. B) Insulin increased V_ATP in WT but not in NaPi2a^−/− mice when mice were infused with 5 mU/kg/min insulin, followed by 3 mU/kg/min of insulin and 12.5 mg/kg/min of 20% glucose at a rate of 2.1 μl/min on the basis of body weight of the animal to maintain euglycemia and hyperinsulinemia during ST-[³¹P]MRS (hyperinsulinemic-euglycemic clamp). C, D) Plasma glucose (C) and insulin (D) values measured after the experiment were not different between the 2 groups. CIP, oxidative phosphorylation capacity of complex I–related substrates. All data are means ± sem; n = 5–8 in each group. *P < 0.05; **P < 0.01 by double-sided Student’s t test.