MITOCHONDRIAL OXIDATIVE FUNCTION IN HUMAN SAPONIN-SKINNED MUSCLE-FIBERS - EFFECTS OF PROLONGED EXERCISE

1. The influence of prolonged exhaustive exercise on mitochondrial oxi dative function was investigated in ten men. 2. Muscle biopsies were t aken before and after exercise and mitochondrial respiration investiga ted in fibre bundles made permeable by pretreatment with 1 saponin. 3. After exercise, respiration in the absence of ADP increased by 18% (P < 0.01), but respiration at suboptimal ADP concentration (0.1 mM) and maximal ADP-stimulated respiration (1 mM ADP) remained unchanged. 4. In the presence of creatine (20 mM), mitochondrial affinity for ADP in creased markedly and respiration at suboptimal ADP concentration (0 1 mM) was similar (pre-exercise) or higher (post-exercise; P < 0.05) tha n with 1 mM ADP alone. The increase in respiratory rate with creatine was correlated to the relative type I fibre area (r = 0.84). Creatine- stimulated respiration increased after prolonged exercise (P < 0 01). 5. The respiratory control index (6. 8 +/- 0.4, mean +/- S.E.M.) and t he ratio between respiration at 0 1 and 1 mM ADP (ADP sensitivity inde x, 0.63 +/- 0.03) were not changed after exercise. The sensitivity ind ex was negatively correlated to the relative type I fibre area (r = -0 .86). 6. The influence of exercise on muscle oxidative function has fo r the first time been investigated with the skinned-fibre technique. I t is concluded that maximal mitochondrial oxidative power is intact or improved after prolonged exercise, while uncoupled respiration is inc reased. The latter finding may contribute to the elevated post-exercis e oxygen consumption. The finding that the sensitivity of mitochondria l respiration for ADP and creatine are related to fibre-type compositi on indicates intrinsic differences in the control of mitochondrial res piration between fibres.