Lemieux 2006 Biochim Biophys Acta
|Lemieux H, Garedew A, Blier PU, Tardif J-C, Gnaiger E (2006) Temperature effects on the control and capacity of mitochondrial respiration in permeabilized fibers of the mouse heart. Biochim Biophys Acta, EBEC Short Reports Suppl 14 (2006):201-2.|
Temperature is among the most important factors affecting metabolic rate. Although mammalian body temperature is ~37 °C, most respiratory studies on heart mitochondria are performed at 25 or 30 °C. In clinical states, heart may face hyperthermia (e.g. fever), or hypothermia (e.g. organ transplant preservation, topical cooling to limit ischemic damage, adjunctive therapy during minimally invasive surgery). Limited information is available on the control of mitochondrial respiratory capacity by temperature in the presence of various energy substrates. In the present study, therefore, temperature effects on mitochondrial respiration were investigated in permeabilized fibers from left ventricles of the mouse. High-resolution respirometers (Oroboros O2k) were operated to measure mitochondrial respiratory capacities simultaneously at five temperatures (4, 25, 30, 37 and 40 °C) for each mouse left ventricle fiber preparation (N³4). At 37 °C, the respiratory control ratio (malate+pyruvate; stimulation by ADP to State 3) was 5.7 ± 1.0 SD, declining to 2.1 ± 0.8 SD at 4 °C. Stimulation of respiration by cytochrome c was significant only at 25 °C. State 3 respiration was significantly higher with malate+pyruvate compared to malate+glutamate at 25 - 40 °C, but this was reversed at 4 °C. Parallel electron input into complexes I+II by addition of succinate to malate+pyruvate+glutamate increased State 3 respiratory flux 1.5- to 2.0-fold at all temperatures. Uncoupling by FCCP did not further stimulate respiration, indicating that the phosphorylation system was not limiting, in contrast to rat heart and human skeletal muscle. At 25 °C, respiratory capacity was reduced to 50 % of normothermic, whereas cooling to 4 °C suppressed respiration to 2.6 %. COX activity was determined with ascorbate (2 mM) and TMPD (0.5 mM) after inhibition of complexes I, II and III. At 25 – 40 °C, COX activity was ~1.3-fold higher than respiration with parallel complex I+II electron input, and >3-fold at 4 °C, but these conditions yield an underestimate of the actual COX excess capacity. These results show that (1) malate+glutamate underestimates complex I capacity by 40 % at physiological temperature, and pyruvate should be added; (2) diagnosis of mitochondrial respiratory function can and should be performed at physiological temperature, using 0.7 mg wet weight of muscle biopsy; and (3) metabolic shutdown of the heart is extensive at 4 °C but incomplete. The present data provide an important baseline for further studies of mouse heart metabolism, including various genetic models of mitochondrial diseases and dysfunction.
Organism: Mouse Tissue;cell: Heart Preparation: Permeabilized tissue, Enzyme, Oxidase;biochemical oxidation
Coupling state: OXPHOS