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. 1998 Jul 1;510 ( Pt 1)(Pt 1):279-86.
doi: 10.1111/j.1469-7793.1998.279bz.x.

Mitochondrial oxidative function in human saponin-skinned muscle fibres: effects of prolonged exercise

M Tonkonogi  1 , B Harris, K Sahlin
Affiliations

Mitochondrial oxidative function in human saponin-skinned muscle fibres: effects of prolonged exercise

M Tonkonogi et al. J Physiol. .

Abstract

1. The influence of prolonged exhaustive exercise on mitochondrial oxidative function was investigated in ten men. 2. Muscle biopsies were taken before and after exercise and mitochondrial respiration investigated in fibre bundles made permeable by pretreatment with 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 increased markedly and respiration at suboptimal ADP concentration (0.1 mM) was similar (pre-exercise) or higher (post-exercise; P < 0.05) than 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 the ratio between respiration at 0.1 and 1 mM ADP (ADP sensitivity index, 0.63 +/- 0.03) were not changed after exercise. The sensitivity index was negatively correlated to the relative type I fibre area (r = -0.86). 6. The influence of exercise on muscle oxidative function has for the first time been investigated with the skinned-fibre technique. It is concluded that maximal mitochondrial oxidative power is intact or improved after prolonged exercise, while uncoupled respiration is increased. The latter finding may contribute to the elevated post-exercise oxygen consumption. The finding that the sensitivity of mitochondrial respiration for ADP and creatine are related to fibre-type composition indicates intrinsic differences in the control of mitochondrial respiration between fibres.

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Figures

Figure 1
Figure 1. Effect of duration of saponin treatment on maximal ADP-stimulated respiration and respiration in the absence of ADP in human skeletal muscle fibres
Values are means ± s.e.m. of 4 (0, 15 and 45 min) or 8 (30 min) fibre bundles. •, 1 mM ADP; ▾, 0 mM ADP.
Figure 2
Figure 2. Mitochondrial respiratory rate before and after prolonged exhaustive exercise
Values are means ± s.e.m. □, 0 mM ADP; formula image, 0.1 mM ADP; formula image, 1 mM ADP; ▪, 0.1 mM ADP + 20 mM creatine. * Significantly different from pre-exercise (P < 0.01,n = 10).
Figure 3
Figure 3. Creatine-induced increase in respiration in relation to relative type I fibre area
Creatine-induced increase in respiration is expressed as: 100 × [(R: 0.1 mM ADP + 20 mM creatine) - (R: 0.1 mM ADP)]/(R: 0.1 mM ADP),where R denotes respiration. Values are the means of pre- and post-exercise samples (r = 0.84; P < 0.01,n = 10; y = 3.6x - 113).
Figure 4
Figure 4. Relationship between ADP sensitivity index and relative type I fibre area
ADP sensitivity index is defined as the ratio of respiration at 0.1 and 1 mM ADP. Values are the means of pre- and post-exercise samples (r = -0.86; P < 0.01,n = 10; y = -0.008x + 1.04).
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