30 days of normobaric hypoxia increases mitochondrial respiration

D.J. Bishop,¹ A. Ferri,^1,2 I. Rivolta,² A. Panariti,² A. Zaza² and G. Miserocchi,² ¹Institute of Sport, Exercise and Active Living (ISEAL) and School of Sport and Exercise Science, Victoria University, Melbourne, VIC 8001, Australia and ²Dipartimento di Medicina Sperimentale, Università degli Studi di Milano-Bicocca, Monza, Italy..

Contrasting increases in cytochrome c oxidase and decreases in mitochondrial volume have been reported in response to stays at high altitude (Hoppeler & Vogt, 2001). However, none of these studies directly measured mitochondrial respiration and all can be criticised for a lack of control for changes in physical activity. The purpose of this study was to investigate the effects 30 days of hypoxia on directly-measured, mitochondrial respiration. Twenty Wistar rats were randomly assigned to 30 days of either normobaric normoxia (CON; 21% O₂) or hypoxia (HYP; 10% O₂). Both submaximal (0.1 mM ADP) and maximal (2 mM ADP) ADP-stimulated mitochondrial respiration were determined on both isolated mitochondria (from lungs) and permeabilised muscle fibres from the left (LV) and right ventricle (RV), and the soleus (SOL) and EDL. Results were analysed using one-way ANOVA (p<0.05). Both submaximal and maximal ADP-stimulated respiration was significantly greater in HYP for SOL and LV, and tended to be higher for RV (p=0.06). There were no significant differences for the EDL. The significantly greater mitochondrial respiration in the LV of HYP (26%; p<0.05) was similar to a previous study (16%, ns) (Novel-Chaté et al., 1998). The non-significantly greater mitochondrial respiration in the RV of HYP is also consistent with previous research (Novel-Chaté et al., 1998) and can probably be attributed to significantly greater mass of the RV. We have shown for the first time however, that there is a greater mitochondrial respiration in the soleus of rats exposed to 30 days of hypoxia.

Hoppeler, H. & Vogt, M. (2001). Muscle tissue adaptations to hypoxia. Journal of Experimental Biology 204, 3133-3139.

Novel-Chaté, V., Mateo, P., Saks, V.A., Hoerter, J.A. & Rossi, A. (1998). Chronic exposure of rats to hypoxic environment alters the mechanism of energy transfer in myocardium. Journal of Molecular and Cellular Cardiology 30, 1295-1303.