Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C27
Lipopolysaccharide-induced endotoxaemia reduces the maximal rate of mitochondrial ATP production in rat skeletal muscle and this effect is specific to the pyruvate dehydrogenase complex
R. P. Atkins1, D. Constantin-Teodosiu1, S. M. Gardiner1, P. L. Greenhaff1
1. Metabolic Physiology, University of Nottingham, Nottingham, United Kingdom.
We have provided evidence of a role for the inhibition of mitochondrial pyruvate dehydrogenase complex (PDC) in the impairment of muscle carbohydrate oxidation in vivo during lipopolysaccharide (LPS)-induced endotoxaemia in the rat(1)(2) and that pro-inflammatory cytokine mediated upregulation of PDK4 transcription is likely to play an important role in this response(3). The aim of the present study was to determine the impact of LPS administration on maximal rates of mitochondrial ATP production and components of the electron transport chain in rodent muscle. Under general anaesthesia (fentanyl citrate/medetomidine 300µg.kg-1 each) Sprague-Dawley rats were implanted with a jugular vein catheter. Reversal/analgesia was provided with atipamezole 1mg.kg-1/buprenorphine 0.02mg.kg-1. Prepared rats received a continuous intravenous infusion of LPS (15 µg.kg-1.h-1) (n=8) or saline for 24 h at 0.4 ml.h-1 (n=7). Animals were terminally anaesthetised with thiobutabarbital sodium (80 mg.kg−1) and the soleus muscles removed. A bio-luminescence technique was used to measure maximal rates of ATP production in isolated mitochondrial suspensions in the presence of a variety of substrates. The activity of components of the mitochondrial electron transport chain, PDC activation status and muscle ATP and lactate content were also determined. Values in the text and Figure 1 represent mean+SEM and statistical comparisons across treatment groups were performed using Student’s unpaired T-test. Muscle ATP content was reduced (control 18.72 ± 1.21 vs LPS 12.96 ± 1.62 mmol.kg-1dm, p<0.05) and lactate content increased (control 2.44 ± 0.82 vs LPS 5.28 ± 0.74 mmol.kg-1dm, p<0.05) following LPS compared to control. Muscle PDC activation status was reduced following LPS compared with control (control 0.43 ± 0.05 vs LPS 0.22 ± 0.05 mmol.min-1.mg protein-1, p<0.05). Mitochondrial ATP production rate in LPS treated animals was reduced compared to control when pyruvate was used as a substrate, but the corresponding rates for the other substrates tested was no different between treatment groups (Figure 1). Assays of mitochondrial complexes (NADH-cytochrome c reductase, succinate dehydrogenase, succinate-cytochrome c reductase and cytochrome c oxidase) revealed no differences in activity between treatment groups. In keeping with previous work(1)(2)(3) LPS administration reduced PDC activation status and increased muscle lactate accumulation. In accordance with this, the maximal rate of mitochondrial ATP production from pyruvate was reduced by 45%. Endotoxaemia therefore impairs skeletal muscle mitochondrial function, and this effect appears to be specific to PDC. Strategies to improve muscle carbohydrate oxidation and mitochondrial function during endotoxaemia should be targeted towards PDC.
Where applicable, experiments conform with Society ethical requirements