Effect of intermittent normobaric hypoxia on kinetic properties of mitochondrial enzymes

We studied the effect of intermittent normobaric hypoxia on the formation of adaptive signs and state of mitochondrial enzymes in the cerebral cortex of rats with different resistance to hypoxia. Kinetic parameters for mitochondrial enzymes in the substrate region of the respiratory chain of the cerebral cortex underwent various changes in low resistant and highly resistant rats over the first 2 h after 1-h intermittent normobaric hypoxia. Low resistant animals were characterized by more effective functioning of rotenone-sensitive NADH-cytochrome C reductase and succinate-cytochrome C reductase under conditions of increased reduction status of the cell. These features correlated with the increase in the general resistance of animals. Significant changes in kinetic properties of mitochondrial enzymes and signs of the development of resistance were not found in highly resistant rats. Reciprocal relations between mitochondrial enzyme complexes in the substrate region of the respiratory chain probably play a role of the signal regulatory mechanism, which mediates tissue-specific and general resistance of rats under conditions of intermittent normobaric hypoxia. These effects did not depend on oxygenation of the inhaled gas mixture during the inter-hypoxic period. __________ Translated from Byulleten’ Eksperimental’noi Biologii i Meditsiny, Vol. 144, No. 12, pp. 644–651, December, 2007     

Effects of chronic hypoxia and endurance training on muscle capillarity in rats

Skeletal muscle capillarity expressed as capillary density (CD), and number of capillaries per fibre (C/F), as well as the mean fibre cross-sectional area (FCSA), were determined in the extensor digitorum longus (EDL), plantaris (PLA) and soleus (SOL) muscles of four groups of eight rodents trained on a swimming exercise programme (T) or maintained sedentary (S), at sea level (SL) or at simulated altitude (HA), barometric pressure 61.7 kPa (463 torr) for 12 weeks. It was shown that both HA exposure and endurance training decreased body and skeletal muscles weights (P<0.001). However, neither HA exposure nor endurance training induce any variation in relative importance in the skeletal muscle mass. Altitude exposure and endurance training had increasing effects on CD in all muscles studied (P<0.001). This study confirms the fact that altitude exposure has no direct effect on capillary development. On the other hand, the capillary supply of the several slow- and fast- twitch skeletal muscles studied is increased by endurance training. This real enhancement in capillary network is ascertained by an increase in the C/F ratio (+7%, +26%, +16%, in PLA, EDL, and SOL muscles, respectively at sea level, and +19.5%, +30%, and +14% respectively at HA). These results indicate that the effects of chronic exercise on skeletal muscle capillarity estimated by the C/F ratio, are greater in an hypobaric environment than in a SL environment.     

Muscle moment arms of pelvic limb muscles of the ostrich (Struthio camelus)

Muscle moment arms were measured for major muscles of the pelvic limb of the ostrich (Struthio camelus) in order to assess specific functional behaviour and to apply this to locomotor performance. Pelvic limbs of six juvenile ostriches were used for this study. The tendon travel technique was used to measure moment arms of 21 muscles at the hip, knee, ankle and metatarsophalangeal joints throughout the ranges of motion observed during level running. Six of the 21 muscles measured were found to have moment arms that did not change with joint angle, whilst the remainder all demonstrated angle-dependent changes for at least one of the joints crossed. Moment arm lengths tended to be longest for the large proximal muscles, whilst the largest relative changes were found for the moment arms of the distal muscles. For muscles where moment arm varied with joint angle: all hip muscles were found to have increasing moment arms with extension of the joint, knee flexors were found to have moment arms that increased with extension, knee extensor moment arms were found to increase with flexion and ankle extensor moment arms increased with extension. The greatest relative changes were observed in the flexors of the metatarsophalangeal joint, for which a three-fold increase in moment arm was observed from flexion to full extension. Changes in muscle moment arm through the range of motion studied appear to optimize muscle function during stance phase, increasing the effective mechanical advantage of these muscles.     

胆道梗阻再通后肝线粒体呼吸功能恢复的实验研究

本文通过复制犬胆道梗阻再通模型，观察了不同梗阻时段的各再通时相肝细胞线粒体呼吸功能损害的恢复情况。结果表明，各组再通后，Ⅲ态氧耗，呼吸控制率及Ｐ／Ｏ值明显下降，在梗阻３周再通组再通后３０天，呼吸控制率可恢复到正常对照组的８８％，Ｐ／Ｏ值于再通后２０天，即可恢复到正常对照组的８９％，而梗阻４周再通组财通后３０天，呼吸控制率及Ｐ／Ｏ值均不能恢复到与正常对照组无显著性差异的水平；在梗阻５周再通组再通后的     

Effect of hypoxia and reoxygenation on mitochondrial function in neonatal myocardium

The effect of hypoxia and reoxygenation on mitochondrial function was studied in the newborn and adult rabbit hearts. In control muscle, mitochondrial state 3 respiration (state 3 QO2), respiratory control index (RCI), energy-dependent calcium uptake, ATP content, and adenine nucleotide translocase in the newborn were significantly greater than in the adult. After 60 min hypoxia, both the newborn and adult showed significant decrease in 1) tissue glycogen, adenine nucleotides, and creatine phosphates and 2) mitochondrial adenine nucleotides, adenine nucleotide translocase, and glutamate-supported state 3 respiration. In the adult, reoxygenation following 60 min hypoxia was not associated with significant recovery in any of the variables described above, and there was significant decrease in the rate of calcium uptake. In the newborn, the values of all variables returned to control except for tissue glycogen and adenine nucleotide translocase. The data suggest that the effect of hypoxia on mitochondrial function in the newborn is less than in the adult. This occurs because of 1) the lower energy demand in the newborn, 2) higher tissue glycogen and higher rates of glycolysis in the newborn, 3) increased degradation and/or efflux of ATP and ADP in the adult, and 4) possibly a difference in the sarcolemmal resistance to hypoxia in the two age groups.     

Muscle growth and fiber type composition in hind limb muscles during postnatal development in pigs

Rapid postnatal development in pigs is reflected by differentiation in skeletal muscle. This process depends on muscle function and demands, but a comprehensive overview of individual developmental characteristics of quickly growing leg muscles in pigs is still missing. This study focused on the development of 10 hind limb muscles in pigs. To determine these changes in mass, fiber type patterns and fiber diameters were analyzed 0, 2, 4, 7, 14, 28, 42, 56 and 400 days after birth. Generally, the proportion of slow fibers increased from birth to 8 weeks. Thereafter, only minor changes in muscle fiber type composition were observed. The majority of the muscles contained less then 10% slow-twitch fibers at birth, increasing to between 12 (Musculus vastus lateralis) and 38% (M. gastrocnemius medialis) in adult pigs. By contrast, postural muscles already had 20-30% slow fibers at birth, and this contribution increased up to 65% in adults (i.e. M. vastus intermedius). From birth to the 2nd week, only in slow fibers could activity of oxidative enzymes be detected. A differentiation of fast-twitch fibers into subtypes with high (comparable to type IIA) and low oxidative metabolism (equivalent to type IIB) occurred between the 2nd and 4th week of life. The ratio between type II fibers with high and low oxidative enzyme activity did not change markedly through development in any muscle, although there was a trend towards an increasing proportion of type IIA fibers in the soleus. In the majority of the muscles investigated, the fast-twitch fibers with low oxidative metabolism (IIB) obtained the largest cross-sectional area. In contrast, at birth no remarkable differences in the diameter of fast and slow fibers were found. The rapid increase in muscle mass compared to body mass reflects the high performance in meat production of the cross pig investigated.     

Corticospinal control of respiratory muscles in chronic obstructive pulmonary disease

Patients with chronic obstructive pulmonary disease (COPD) face an increased respiratory load and in consequence have an elevated respiratory drive. We used transcranial magnetic stimulation (TMS) to investigate associated changes in corticospinal excitability both at rest and during voluntary facilitation at different levels of inspiratory effort. Diaphragm and abdominal motor thresholds were significantly lower in COPD than healthy controls, but the quadriceps response was the same. In patients there was a significant increase in diaphragm response from rest during 20% inspiratory efforts but no further increase with greater efforts. In controls there was a further stepwise increase at 40% and 60% of inspiratory effort. The cortical silent period was significantly shorter in COPD. Using paired stimulation to study intracortical inhibitory and excitatory circuits we found significantly less excitability of intracortical facilitatory circuits in patients at long (>7 ms) interstimulus intervals. These results suggest that there is a ceiling effect in motor control output to the respiratory muscles of patients with COPD.     

Effects of five nights of normobaric hypoxia on the ventilatory responses to acute hypoxia and hypercapnia

This study examined the effects of five nights of normobaric hypoxia on ventilatory responses to acute isocapnic hypoxia (AHVR) and hyperoxic hypercapnia (AHCVR). Twelve male subjects (26.6 +/- 4.1 years, standard deviation (S.D.)) slept 8-9 h per day overnight for 5 consecutive days at a simulated altitude of 4,300 m (FiO2= approximately 13.8%). Using the technique of dynamic end-tidal forcing, the AHVR and AHCVR were assessed twice prior to, immediately after, and 5 days following the hypoxic exposure. Immediately following the exposure, AHVR was increased by 1.6 +/- 1.3 L min(-1) %(-1) (P<0.01) when compared with control values. Likewise, after the exposure, ventilation in hyperoxia was increased (P<0.001) and was associated with both an increase in the slope (1.5 +/- 1.4 L min(-1) Torr(-1); P<0.05) and decrease in the intercept (-2.7 +/- 4.3 Torr; P<0.05) of the AHCVR. These results show that five nights of hypoxia can elicit similar perturbations, in both AHVR and AHCVR, as have been reported during more chronic altitude exposures.     

中等强度训练干预大鼠骨骼肌抗增殖蛋白PHB1表达及线粒体呼吸功能的变化

背景:研究显示长期中等强度规律运动可以改善骨骼肌细胞线粒体电子呼吸链复合体酶的活性,从而提高其做功能力和抵抗疲劳能力。目的:探讨中等强度训练对大鼠骨骼肌内抗增殖蛋白及线粒体呼吸功能的影响。方法:32只健康雄性SD大鼠随机分为2组:安静对照组、中等强度训练组,每组16只。中等强度训练组的训练方案:第1周以10 m/min速度跑,每周6 d,每天10 min,坡度10°;第2周以15 m/min速度跑,每周6 d,每天增加10 min至60 min结束,坡度10°;第3-8周以15 m/min速度跑,每周6 d,每天60 min,坡度10°。末次实验后48 h处死大鼠,提取骨骼肌以及线粒体,检测线粒体呼吸控制率、ATP含量、活性氧水平、复合体V活性及PHB1蛋白表达。结果与结论:①与安静对照组相比,中等强度训练组骨骼肌线粒体呼吸控制率显著性升高(P<0.001)、ATP含量显著性升高(P<0.05)、活性氧水平显著降低(P<0.001)、复合体V活性显著升高(P<0.05)、PHB1表达显著升高(P<0.01);②通过相关性分析得出:经过8周中等强度训练后大鼠骨骼肌内PHB1的表达分别与ATP含量、复合体V活性呈正相关,与活性氧水平呈负相关;③结果表明,中等强度训练通过促进PHB1表达提高线粒体氧化磷酸化功能,维持线粒体膜结构,增强线粒体呼吸功能。     

Effects of acute and chronic endurance exercise on mitochondrial uncoupling in human skeletal muscle

Mitochondrial proteins such as uncoupling protein 3 (UCP3) and adenine nucleotide translocase (ANT) may mediate back-leakage of protons and serve as uncouplers of oxidative phosphorylation. We hypothesized that UCP3 and ANT increase after prolonged exercise and/or endurance training, resulting in increased uncoupled respiration (UCR). Subjects were investigated with muscle biopsies before and after acute exercise (75 min of cycling at 70% of     ) or 6 weeks endurance training. Mitochondria were isolated and respiration measured in the absence (UCR or state 4) and presence of ADP (coupled respiration or state 3). Protein expression of UCP3 and ANT was measured with Western blotting. After endurance training     , citrate synthase activity (CS), state 3 respiration and ANT increased by 24, 47, 40 and 95%, respectively (all   P < 0.05  ), whereas UCP3 remained unchanged. When expressed per unit of CS (a marker of mitochondrial volume) UCP3 and UCR decreased by 54% and 18%  ( P < 0.05)  . CS increased by 43% after acute exercise and remained elevated after 3 h of recovery  ( P < 0.05)  , whereas the other muscle parameters remained unchanged. An intriguing finding was that acute exercise reversibly enhanced the capacity of mitochondria to accumulate Ca²⁺  ( P < 0.05)  before opening of permeability transition pores. In conclusion, UCP3 protein and UCR decrease after endurance training when related to mitochondrial volume. These changes may prevent excessive basal thermogenesis. Acute exercise enhances mitochondrial resistance to Ca²⁺ overload but does not influence UCR or protein expression of UCP3 and ANT. The increased Ca²⁺ resistance may prevent mitochondrial degradation and the mechanism needs to be further explored.     

急、慢性低氧对大鼠脑线粒体蛋白翻译合成的影响

目的:探讨模拟高原低氧对大鼠脑线粒体蛋白合成功能的影响。方法:雄性wistar大鼠随机分为急性低氧组、慢性低氧组和平原对照组。急、慢性低氧组动物分别连续暴露于模拟4000m高原3d和40d, 分离脑线粒体, 用[³H]-亮氨酸掺入法测定线粒体体外翻译活性, [³⁵S]-蛋氨酸掺入并对翻译后产物经SDS-PAGE和放射自显影进行分子量鉴定。结果:急性低氧脑线粒体蛋白翻译活性明显低于对照组60%(P<0.01), 慢性低氧时线粒体翻译活性与对照组无显著差异(P>0.05), 但显著高于急性低氧组(P<0.05).急性与慢性低氧暴露均未发现线粒体蛋白体外翻译产物与平原对照组有质的差异。结论:低氧可影响线粒体DNA编码蛋白合成, 并且与低氧暴露时间有关。     

Redox modulation of contractile function in respiratory and limb skeletal muscle

For the last half century, scientists have studied the biological importance of free radicals in respiratory and limb muscles. We now know that muscle fibers continually produce both reactive oxygen species (ROS) and nitric oxide (NO) and that both cascades play critical roles in contractile regulation. Under basal conditions, muscle-derived ROS and NO exert opposing effects. Low-level ROS activity is an essential part of the homeostatic milieu and is required for normal force production whereas NO derivatives function as a brake on the system, limiting force. The modulatory effects of ROS and NO are disrupted by conditions that exaggerate production including mechanical unloading, inflammatory disease, and strenuous exercise. Marked increases in ROS or NO levels cause contractile dysfunction, resulting in muscle weakness and fatigue. These principles provide a foundation for ongoing research to identify the mechanisms of ROS and NO action and develop interventions that protect muscle function.     

Effects of training in normoxia and normobaric hypoxia on human muscle ultrastructure

The adaptive response of skeletal muscle to training in normoxia and in severe normobaric hypoxia was studied. The first group of five male subjects trained for 3 weeks on a bicycle (2 h/day, 6 days/week) in normoxia (Control training, Con T). A second group of five subjects trained in an ambient FIO₂ decreasing progressively from 12.7% to a final level of 10.0% (hypoxic training, Hyp T). Fourteen months later, these subjects trained in normoxia at the same absolute power (normoxic training, Nor T). Peak oxygen consumption ( O₂ max) was measured in normoxic and hypoxic conditions. Biopsies from the vastus lateralis muscle were analysed for fibre size, capillary and ultrastructural composition. Nor T had no effect on muscle tissue or O₂ max. Con T increased volume density of total mitochondria and lipids by 36 and 135% respectively (P<0.05). Hyp T induced a 10% increase (P<0.05) in peak O₂ max measured in hypoxia. Mean fibre cross-sectional area, interfibrillar mitochondrial volume density and capillary-to-fibre ratio were increased (P<0.05) by 10, 42 and 13% respectively in the Hyp T group. These results suggest that training at the same relative workload in normoxia and hypoxia have similar, but not identical, effects on muscle tissue. If training in normoxia is carried out at the same absolute workload as in severe hypoxia, no significant effects are observed.     

Microvascular angioadaptation after endurance training with L-arginine supplementation in rat heart and hindleg muscles

This study was designed to examine whether dietary L-arginine supplementation modulates exercise-induced angiogenesis and vascular endothelial growth factor (VEGF) expression in female Wistar rats. Exercise training (running) lasted for 6 weeks at 25 m min-1 on a 20% gradient for 10-60 min day-1. Rats in the L-arginine-treated groups drank water containing 4% L-arginine. Histochemical identification of capillary profiles showed that training with L-arginine significantly increased the capillary/fibre (C/F) ratio in the subendocardium of the left ventricle, whereas training alone did not. Because of a significantly higher fibre cross-sectional area, a concomitant, but not significant, decrease in capillary density was also observed. In the hindleg muscles, training with L-arginine significantly increased the C:F ratio, although the degree of change was the same as that observed after training alone. Western blot analysis showed that training with L-arginine significantly increased VEGF protein expression by 1.7-fold in the left ventricle, while the increase with training alone was insignificant. In the soleus muscle, although VEGF protein expression was elevated insignificantly after training (2.8-fold), training with L-arginine significantly increased the protein levels (3.8-fold). Tissue endothelial nitric oxide synthase protein levels did not changed after either training or L-arginine treatment. The present results suggest that L-arginine supplementation causes additional effects on exercise-induced angiogenesis in the rat heart by promoting VEGF expression.     

Typology of the respiratory muscles in normal men and in patients with moderate chronic respiratory diseases

Histochemical muscle fibre composition was studied in biopsies from the diaphragm, the external and internal intercostal muscles in the fifth intercostal space and horizontal and vertical parts of the serratus in 8 subjects with normal lung function and in 18 patients with abnormal lung function (6 restrictive and 12 obstructive). Muscle fibres were classified as type I (slow twitch) or type II (fast twitch) on the basis of their myofibrillar ATPase pH lability. All the muscles studied showed a mosaic pattern with the two fibre types. In every respiratory muscle, the percentage of type I fibres was higher than 50%. There was no significant difference between the three groups (normal, restrictive and obstructive) for each of the six muscles studied. The fibre diameters were similar for all types and muscles (range of means: 41-63 micron), except for the diaphragm in which the diameters of type I and type II fibres were significantly higher in the normal subjects as compared to the obstructive and restrictive patients. Moreover, there was a significant linear correlation between the diameter of the diaphragmatic fibres and vital capacity and FEV1. A low "atrophy factor" was found for each muscle studied with a large intra-individual variation. The results support the idea that the increased respiratory loading due to disease do not hypertrophy the respiratory muscles and suggest that the effect of the disease on the respiratory muscles is more related to the increased mechanical impedance of the respiratory system rather than to the changes in thoracic configuration.     

Dynamic changes of deleted mitochondrial DNA in human leucocytes after endurance exercise

We examined the time course of the appearance and disappearance of deleted mitochondrial DNA (mtDNA) in human leucocytes after endurance exercise. Five untrained healthy females [aged 20.2 (0.4) years] exercised for 30 min at 50–60 W at 60 rpm on a cycle ergometer for 2 or 3 consecutive days. Blood samples were collected immediately before exercise, and on three occasions after the end of the last exercise bout. Levels of mtDNA were analyzed using the nested polymerase chain reaction method. Prior to exercise, a common mtDNA deletion was identified in all subjects. This common deletion was again identified in all subjects 1 day after completion of the exercise regime. However, mtDNA with this common deletion was found to have disappeared 2 days after exercise in three subjects, and after 4 days in the other two subjects. The deletion then reappeared 5 or 6 days after the final exercise bout in three of the five subjects. These findings demonstrate that a common deletion in leucocytes disappears over a period of several days after endurance exercise and reappears a number of days thereafter. Therefore, the status of the appearance and disappearance of common mtDNA deletion in leucocytes is highly dynamic. Electronic Publication