This study explores the importance of creatine kinase (CK) in the regulation of muscle mitochondrial respiration in human subjects depending on their level of physical activity. Volunteers were classified as sedentary, active or athletic according to the total activity index as determined by the Baecke questionnaire in combination with maximal oxygen uptake values (peak ◊ O 2 , expressed in ml min _1 kg _1 ). All volunteers underwent a cyclo-ergometric incremental exercise test to estimate their peak ◊ O 2 and ◊ O 2 at the ventilatory threshold (VT). Muscle biopsy samples were taken from the vastus lateralis and mitochondrial respiration was evaluated in an oxygraph cell on saponin permeabilised muscle fibres in the absence (◊ 0 ) or in the presence (◊ max ) of saturating [ADP]. While ◊ 0 was similar, ◊ max differed among groups (sedentary, 3.7 ± 0.3, active, 5.9 ± 0.9 and athletic, 7.9 ± 0.5 mmol O 2 min _1 (g dry weight) _1). ◊ max was correlated with peak ◊ O 2 (P < 0.01, r = 0.63) and with ◊ T (P < 0.01, r = 0.57). There was a significantly greater degree of coupling between oxidation and phosphorylation (◊ max /◊ 0 ) in the athletic individuals. The mitochondrial K m for ADP was significantly higher in athletic subjects (P < 0.01). Mitochondrial CK (mi-CK) activation by addition of creatine induced a marked decrease in K m in athletic individuals only, indicative of an efficient coupling of mi-CK to ADP rephosphorylation in the athletic subjects only. It is suggested that increasing aerobic performance requires an enhancement of both muscle oxidative capacity and mechanisms of respiratory control, attesting to the importance of temporal co-ordination of energy fluxes by CK for higher efficacy.

In these patients, the disease-specific muscle metabolic impairments derive mostly from extramitochondrial mechanisms that disrupt the normal symmorphosis relations. The possible roles of ACE inhibitors and level of activity are discussed.

As energetic metabolism is crucial for muscles, they develop different adaptations to respond to fluctuating demand among muscle types. Whereas quantitative characteristics are known, no study described simultaneously quantitative and qualitative differences among muscle types in terms of substrates utilization patterns. This study thus defined the pattern of substrates preferential utilization by mitochondria from glycolytic gastrocnemius (GAS) and oxidative soleus (SOL) skeletal muscles and from heart left ventrical (LV) in rats. We measured in situ, ADP (2 mM)-stimulated, mitochondrial respiration rates from skinned fibers in presence of increasing concentrations of pyruvate (Pyr) + malate (Mal), palmitoyl-carnitine (Palm-C) + Mal, glutamate (Glut) + Mal, glycerol-3-phosphate (G3-P), lactate (Lact) + Mal. Because the fibers oxygen uptake (Vs) followed Michaelis-Menten kinetics in function of substrates level we determined the Vs and Km, representing maximal oxidative capacity and the mitochondrial sensibility for each substrate, respectively. Vs were in the order GAS < SOL < LV for Pyr, Glu, and Palm-C substrates, whereas in the order SOL = LV < GAS with G3-P. Moreover, the relative capacity to oxidize Palm-C is extremely higher in LV than in SOL. Vs was not stimulated by the Lact substrate. The Km was equal for Pyr among muscles, but much lower for G3-P in GAS and lower for Palm-C in LV. These results demonstrate qualitative mitochondrial tissue specificity for metabolic pathways. Mitochondria of glycolytic muscle fibers are well adapted to play a central role for maintaining a satisfactory cytosolic redox state in these fibers, whereas mitochondria of LV developed important capacities to use fatty acids.

In chronic obstructive pulmonary disease, inspiratory muscles face increased resistive and elastic workloads and therefore increased energy requirements. The adaptive response of these muscles to this higher energy demand includes increased oxidative enzymes and changes in contractile protein expression but the consequences on mitochondrial function and energy metabolism have not been assessed so far. We investigated the in situ properties of the mitochondria of costal diaphragm and external intercostal muscles using the skinned fiber technique in 9 emphysematous and 11 age-matched control patients. Biopsies obtained during thoracic surgery were placed in an oxygraphic chamber to measure maximal oxygen uptake. We observed that the maximal oxidative capacity of diaphragm and external intercostal muscles increased significantly in the emphysematous group compared with the control group (+135 and +37%, respectively). Significant correlations were found between the maximal oxidative capacity and patients' pulmonary indexes of obstruction (diaphragm: r = -0.637, intercostal: r = -0.667, p < 0.005) and hyperinflation (diaphragm: r = 0.639, p < 0.003, intercostal: r = 0.634, p < 0.01). Slow myosin heavy chain isoform increased in the diaphragm of the emphysematous group, with significant relationships between indexes of obstruction and hyperinflation and activities of biochemical mitochondrial markers. Thus, severe emphysema was associated with increased mitochondrial capacity and efficiency in the inspiratory muscles, supporting an endurance training-like effect.