EFFECT OF INSPIRATORY TRAINING ON MITOCHONDRIAL-DNA AND CYTOCHROME-C-OXIDASE EXPRESSION IN THE DIAPHRAGM

We have previously shown that respiratory training with inspiratory fl ow-resistive (IFR) loads improves diaphragm performance and is associa ted with an increase in cytochrome-e oxidase (COX) activity (1). The p resent study was conducted to define the level at which the increase i n COX activity is controlled. Six sheep were trained with IFR loads fo r 3 h/day for 3 wk. The diaphragm was sampled from the six trained she ep and from six control sheep. Quantitative DNA and RNA slot-blot anal yses with mitochondrially coded COX subunit III and nuclearly coded su bunit IV probes and immunoblotting with anti-COX holoenzyme antibodies were performed. We found that in the diaphragm the amount of COX subu nit proteins coded in either genetic system was greater in the trained than in the control sheep. Neither the amount of mitochondrial DNA no r mRNA for COX subunits was different between the two groups. We concl ude that the increase in COX activity in the diaphragm after chronic r espiratory training is determined by the amount of subunit proteins, p ossibly involving translation/degradation of these proteins.