TI - Mitochondrial oxygen consumption and respiratory coupling . . AB - The absence of reduced cardiac efficiency was unexpected and revealed an important difference between the type 1 diabetic Akita mouse and type 2 diabetic mouse models . Because mitochondrial uncoupling may underlie impaired cardiac efficiency in type 2 diabetic hearts ( 1,5,6 ) , we hypothesized that mitochondrial coupling would be normal in Akita hearts . Mitochondrial function was initially evaluated in fibers that were prepared from freshly isolated mouse hearts . In hearts from 24-week-old mice , maximal ADP -stimulated mitochondrial oxygen consumption (VADP) and ATP synthesis were unchanged using palmitoyl carnitine as a subSTRate ( Fig 3A and E ) , but VADP and ATP synthesis were significantly reduced in Akita mice using pyruvate ( Fig 3B and F ) or glutamate ( Fig 3C and G ) as SUBstrates . Although a respiratory defect was evident , there was no evidence for mitochondrial uncoupling . Rates of oligomycin-insensitive respirations ( Voligo ) and ATP-to-O ratios were unchanged with any SUBstrate , indicating intact coupling of ATP synthesis to oxygen consumption . In 10-week-old mice , similar reductions in glutamate-supported respirations (VADP) were observed ( Fig 3D ) . ATP synthesis rates were proportionately reduced ; thus , ATP-to-O ratios were not different ( Fig 3H ) . We previously reported that mitochondrial uncoupling became evident in ob/ob and db/db mouse hearts after hearts were perfused with increased concentrations of fatty acids ( 5,6 ) . Thus , palmitoyl carnitine respirations were determined in permeabilized fibers from hearts of 10-week-old Akita and control mice after perfusion with 11 mmol/l glucose and 1 mmol/l palmitate ( Fig 4A and B ) . Under these conditions , we observed no differences in VADP , Voligo , ATP production rates or ATP-to-O ratios . Finally , to provide more definitive evidence for the absence of mitochondrial uncoupling in Akita hearts , we isolated mitochondria from hearts of 24-week-old Akita mice after perfusion of hearts with 11 mmol/l glucose and 1 mmol/l palmitate and measured proton leak kinetics ( Fig 4C ) . Proton leak kinetics curves were entirely overlapping between mitochondria from Akita mice and nondiabetic controls , indicating the absence of mitochondrial uncoupling .