Effect of inspiratory training on mitochondrial DNA and cytochrome-c oxidase expression in the diaphragm.

We have previously shown that respiratory training with inspiratory flow-resistive (IFR) loads improves diaphragm performance and is associated with an increase in cytochrome-c oxidase (COX) activity (1). The present study was conducted to define the level at which the increase in COX activity is controlled. Six sheep were trained with IFR loads for 3 h/day for 3 wk. The diaphragm was sampled from the six trained sheep and from six control sheep. Quantitative DNA and RNA slot-blot analyses with mitochondrially coded COX subunit III and nuclearly coded subunit IV probes and immunoblotting with anti-COX holoenzyme antibodies were performed. We found that in the diaphragm the amount of COX subunit proteins coded in either genetic system was greater in the trained than in the control sheep. Neither the amount of mitochondrial DNA nor mRNA for COX subunits was different between the two groups. We conclude that the increase in COX activity in the diaphragm after chronic respiratory training is determined by the amount of subunit proteins, possibly involving translation/degradation of these proteins.