Endurance training limits the functional alterations of rat heart mitochondria submitted to in vitro anoxia-reoxygenation

BACKGROUND: Studies analysing the effect of endurance training on heart mitochondrial function submitted to in vitro anoxia-reoxygenation (A-R) are missing. The present study aimed to investigate the effect of moderate endurance treadmill training (14 weeks) against rat heart mitochondrial dysfunction induced by in vitro A-R. METHODS: Respiratory parameters (state 3, state 4, ADP/O and respiratory control ratio-RCR) and oxidative damage markers (carbonyl groups and malondialdehyde) were determined in isolated mitochondria before and after 1 min anoxia followed by 4 min reoxygenation. Levels of heat shock protein 60 kDa (HSP60) and 70 kDa (HSP70) were measured before A-R in mitochondria and whole muscle homogenate, respectively. RESULTS: A-R significantly impaired the rate of state 3 and state 4 respiration, as well as the RCR and ADP/O in the sedentary group. However, mitochondrial state 3 respiration was significantly higher in trained than in the sedentary group both before and after A-R. The impairments in RCR, ADP/O ratio and state 4 induced by A-R in sedentary group were significantly attenuated in endurance-trained group. The inhibition of state 4 induced by GDP was significantly higher in trained than in sedentary group. Oxidative modifications of mitochondrial proteins and phospholipids were found in sedentary group after A-R, although limited in trained group. Increased levels of mitochondrial HSP60 and tissue HSP70 accompanied the lower decrease in the respiratory function after A-R observed in trained group. CONCLUSION: We therefore concluded that endurance training limited the impairments on rat heart mitochondria caused by the oxidant insult inflicted by in vitro A-R.     

Alterations of liver mitochondrial bioenergetics in diabetic Goto-Kakizaki rats.

Respiratory indexes and the transmembrane electrical potential (delta psi) were evaluated in mitochondrial preparations from 6-month-old Goto-Kakizaki (GK) and Wistar rats in the presence of glutamate + malate and succinate. We found that in diabetic GK mitochondria, flavin adenine dinucleotide (FAD)-linked respiratory indexes (respiratory control ratio [RCR] and adenosine diphosphate [ADP] to oxygen ratio [ADP/O]) are increased and uncoupled respiration is largely enhanced, indicating increased respiratory chain activity in GK rats. Delta psi development in GK mitochondrial preparations, energized using glutamate + malate or succinate as substrates, and the repolarization rate upon phosphorylation of the added ADP were significantly higher in GK mitochondrial preparations. These results indicate an enhanced activity of the phosphorylation system, confirmed by evaluating delta psi development when the mitochondria are energized by adenosine triphosphate (ATP). Moreover, recovery of the potential upon a phosphorylative cycle is increased in GK mitochondria, reflecting a more efficient coupling between the phosphorylative and oxidative system. Contrasting with results obtained for alloxan- or streptozotocin-induced diabetic rats, this study clearly demonstrates no impairment of mitochondrial bioenergetics in diabetic GK rats. On the contrary, at this age, we observed a higher efficiency of the phosphorylation system as compared with Wistar rats.     

The effect of pancreatitis associated ascitic fluid on some functions of rat liver mitochondria. A possible mechanism of the damage to the liver in acute pancreatitis

The damage to the liver during acute pancreatitis (AP) could be partly dependent on depressive action of pancreatitis associated ascitic fluid (PAAF) on the energy metabolism of hepatocytes. The aim of the study was to assess the effect of PAAF from dogs with acute experimental pancreatitis (AEP) and from humans with AP on the respiratory function of isolated rat liver mitochondria (RLM). The mitochondrial oxygen consumption rate in state 3 respiration (with ADP) and in state 4 (without ADP) using sodium succinate as substrate and oxygen Clark's electrode was estimated. Respiratory control ratio (RCR) and P/O ratio were calculated. PAAF was collected after 6 h of AEP induced by Elliott's method in 8 dogs, and from 4 patients with AP, intraoperatively. Both animal and human PAAFs increase the oxygen consumption rate by RLM in state 4 dose dependently (by 65% with 50 microL to 150% with 200 microL of canine PAAF). This uncoupling effect of human PAAF was twice more potent than the canine. Dialysis of PAAF reduced this effect almost completely. The mitochondrial ATPase activity in RLM treated with PAAF was stimulated and this effect was also reduced by dialysis. The conclusion was that the damage to the liver in AEP could be partly dependent on the toxicity of dializable component(s) of PAAF on the energy metabolism of mitochondria. These findings may partly explain the beneficial effects of peritoneal lavage in acute pancreatitis.     

Effects of endurance training and acute doxorubicin treatment on rat heart mitochondrial alterations induced by in vitro anoxia-reoxygenation

Endurance training (ET) and adriamycin (ADR) treatment are two conditions that have been described as triggering metabolic alterations within the myocardium. ADR is an anti-neoplastic agent with notorious cardiotoxicity, most likely because it increases oxidative stress. ET and/or ADR treatment can induce metabolic and signaling alterations affording cross-tolerance against several insults such as ischemia and reperfusion. The objective of the present work was to investigate whether heart mitochondria isolated from rats submitted to ET with or without ADR treatment were more or less susceptible to in vitro anoxia-reoxygenation (AR) when compared with control rats. Twenty-four male Wistar rats were assigned into four groups (n=6 each): control (C), ADR (20 mg-kg⁻¹), 14 wk ET (T), and T+ADR. Respiratory parameters and oxidative damage were determined before and after 1 min anoxia followed by 4 min reoxygenation. Basal heat shock proteins (HSPs)60 and-70 and antioxidant enzymes' activity were measured. ADR by itself decreased state 3 and respiratory control ratio (RCR), as opposed to ET by itself, which improved state 3 and RCR. As expected, AR impaired state 3 and 4, RCR, and ADP/O in the C group (p>0.05). In the ADR group, AR did not induce any alteration in RCR and in ADP/O values. ET in the absence of ADR treatment prevented the impairment in RCR and ADP/O and in state 4 induced by AR. Also, despite the fact that state 3 respiration after AR was lower in all groups, it was significantly higher in the T than in the C group. Increased mitochondrial carbonyls and malondialdehyde (MDA) after AR were only found in the C group. Also, following AR, both carbonyls and MDA levels were lower in the T and in the T+ADR than in C and ADR groups, respectively. HSP60 levels were higher in the ADR, T, and T+ADR than in the C group (2.5-fold, 2-fold, and 1.9-fold increase, respectively). HSP70 increased twofold in the T and T+ADR groups. ET augmented 1.5-fold the activity of superoxide dismutase. The present work demonstrates that both ET and ADR treatment induced myocardial alterations that interfere with in vitro mitochondrial responses to AR.     

Hepatic mitochondrial and lysosomal alterations in acute experimental pancreatitis with ethanolic coetiology in rats

In order to assess the cumulative effects of antecedent acute ethanol intake and acute pancreatitis on the liver, the mitochondrial respiratory functions and lysosomal membrane integrity of the liver were evaluated in taurocholate pancreatitis (AP) in rats, induced 6 hr after intragastric ethanol 40% (5 g/kg body wt). The oxygen consumption rate. RCR (respiratory control ratio), and ADP/O ratio were measured according to Estabrook. Fractional free activity of lysosomal hydrolases was assayed. RCR with glutamate+malate was most decreased at 12 hr of AP with partial improvement after 18 hr. The ADP/O ratio dropped maximally after 18 hr of AP. The fragility of lysosomal membranes increased significantly at 18 hr of AP. The antecedent ethanol intake abolished the partial restoration of RCR after 18 hr; however, it did not affect the ADP/O ratio or the integrity of lysosomal membranes impaired in AP at this time. In conclusion, the antecedent acute ethanol abuse could aggravate the liver mitochondrial deterioration, but not the lysosomal membrane labilization seen in AP.Sponsored by Polish Committee for Scientific Research (KBN) grant 4 0435 91 01.     

Effects of adenoviral overexpression of uncoupling protein-2 and -3 on mitochondrial respiration in insulinoma cells

The brown adipose tissue uncoupling protein 1 (UCP1) catalyzes proton reentry without ATP synthesis, thereby dissipating energy as heat. In contrast, the function(s) of the recently described homologs, UCP2 and UCP3, are less clear. The aim of the present study was to determine whether overexpressed UCP subtypes affect mitochondrial respiration and substrate oxidation in cultured insulin-secreting INS-1 insulinoma cells. Adenoviral overexpression of UCP2 significantly decreased the ADP/O ratio by 31% and 39% in comparison to beta-galactosidase (beta-gal) or the mitochondrial protein manganese superoxide dismutase (MnSOD), respectively, and increased state 4 respiration in the presence of succinate and oligomycin by 52% and 59% in comparison to beta-gal or MnSOD, respectively. Adenoviral overexpression of UCP3 also decreased the ADP/O ratio by 18% (nonsignificant) and increased state 4 respiration by 24% (nonsignificant) in comparison to ss-gal and significantly decreased the ADP/O ratio by 32% and increased state 4 respiration by 35% in comparison to MnSOD. Both UCP2 and UCP3 expression significantly increased whole cell lipid oxidation by 34% (P < 0.01) and 30% (P < 0.05), respectively, compared with cells expressing Ad5CMVlacZ. However, glucose oxidation was not significantly altered by UCP2 or UCP3 expression. Adenoviral UCP2 expression, but not UCP3 (compared with beta-gal), significantly inhibited insulin secretion in the presence of 15 mM glucose [6.17 +/- 0.42 ng/mg cell protein for beta-gal compared with 4.69 +/- 0.39 for UCP2 (P < 0.05) and 5.51 +/- 0.50 for UCP3]. Both overexpressed UCPs significantly reduced INS-1 cell ATP content. Within certain limitations, which are discussed, these data are the first to demonstrate increased respiration and impaired coupling of oxidative phosphorylation as a result of UCP homolog expression in isolated mammalian mitochondria. Our results also suggest an important role for UCP in lipid metabolism and, possibly, insulin secretion.     

补肾复方抗老年大鼠肝肾线粒体老化的实验研究

目的　观察补肾复方抗老年大鼠肝肾线粒体老化的作用 ,为“肝肾同源”提供实验依据。方法　实验大鼠分青年和老年组 ,其中老年组分空白对照组和补肾复方治疗组。采用荧光光度计测定肝肾线粒体内膜流动性 ,比色测磷法测定肝肾线粒体内膜 ATP酶活力 ,生物组织测氧仪测定肝肾线粒体氧化磷酸化效率 (ADP/ O)及呼吸控制率 (RCR) ,透射电镜观察肝肾线粒体形态及形态计量学分析。结果　老年大鼠肝肾线粒体内膜流动性、ATP酶活力、ADP/ O和 RCR均较青年组明显降低 ,而服用补肾复方 2个月后的老年大鼠上述指标均明显增高 (P<0 .0 5或 P<0 .0 1 ) ;透射电镜形态及形态计量学分析结果表明 ,老年组肝肾线粒体肿胀变性 ,补肾复方治疗后 ,肝肾线粒体超微结构变化得到明显改善 (P<0 .0 5或 P<0 .0 1 )。结论　补肾复方对老年大鼠肝肾线粒体老化的结构和功能均有一定的防护 ,线粒体可能是“肝肾同源”的重要物质基础之一。     

螺内酯对截肢创伤致大鼠心肌线粒体损伤的拮抗

目的 研究创伤后大鼠心肌线粒体呼吸功能的改变及螺内酯干预的效果。方法 采用手术的方法建立大鼠左后肢截肢创伤模型,雄性SD大鼠24只,随机分为正常对照组（仅麻醉）、创伤对照组（麻醉后截肢）和螺内酯组（20mg/Kg的螺内酯连续灌胃6 d,麻醉后截肢）,每组8只,观察各组大鼠心肌线粒体呼吸控制率(respiratory control ratio,RCR)、磷氧比值(oxidative phosphorylation ratio、P/O)、总ATP酶、膜电位(mitochondrial transmembrane potential,ΔΨm)的变化。结果 创伤对照组RCR、P/O、总ATP酶和ΔΨm, 均较正常对照组显著降低(P<0.01),与创伤对照组比较,螺内酯干预后,RCR、总ATP酶和ΔΨm均得到改善(P<0.05), P/O变化不显著。结论 截肢创伤可导致心肌线粒体功能下降,螺内酯干预可减轻线粒体损伤,提示醛固酮可能参与了创伤后心肌线粒体的损伤。     

缺血后适应心肌线粒体能量代谢研究

目的研究缺血后适应心肌线粒体能量代谢特点。方法以Langendofff离体心脏灌注系统构建缺血后适应大鼠模型,随机分为对照组．再灌注组和后适应组,每组16只。平衡20min后,对照组灌注60min;再灌注组停灌30min,再灌注30min;后适应组停灌30min之后,循环6次再灌注10s,停灌10s,再灌注28min。记录心率和冠状动脉流量。冉灌注末取心肌．用高效液相色谱法测定高能磷酸化合物三磷腺苷、二磷腺苷和一磷腺苷含量;用差速离心法提取心肌线粒体,用氧电极法测定线粒体3态呼吸、4态呼吸和线粒体呼吸控制率。结果与再灌注组比较,后适应组明显提高再灌注末的心率和冠状动脉流量,明显提高心肌内二磷腺苷和一磷腺苷含量,三磷腺苷在各组差异无统计学意义。线粒体3态呼吸和线粒体呼吸控制率改善。结论心肌线粒体能量代谢改善,是缺血后适应心肌保护的可能机制之一。     

High phosphorylation efficiency and depression of uncoupled respiration in mitochondria under hypoxia

Mitochondria are confronted with low oxygen levels in the microenvironment within tissues; yet, isolated mitochondria are routinely studied under air-saturated conditions that are effectively hyperoxic, increase oxidative stress, and may impair mitochondrial function. Under hypoxia, on the other hand, respiration and ATP supply are restricted. Under these conditions of oxygen limitation, any compromise in the coupling of oxidative phosphorylation to oxygen consumption could accentuate ATP depletion, leading to metabolic failure. To address this issue, we have developed the approach of oxygen-injection microcalorimetry and ADP-injection respirometry for evaluating mitochondrial function at limiting oxygen supply. Whereas phosphorylation efficiency drops during ADP limitation at high oxygen levels, we show here that oxidative phosphorylation is more efficient at low oxygen than at air saturation, as indicated by higher ratios of ADP flux to total oxygen flux at identical submaximal rates of ATP synthesis. At low oxygen, the proton leak and uncoupled respiration are depressed, thus reducing maintenance energy expenditure. This indicates the importance of low intracellular oxygen levels in avoiding oxidative stress and protecting bioenergetic efficiency.     

Protective effect of metronidazole on uncoupling mitochondrial oxidative phosphorylation induced by NSAID: a new mechanism

BACKGROUND: The pathogenesis of non-steroidal anti-inflammatory drug (NSAID) enteropathy is complex. It involves uncoupling of mitochondrial oxidative phosphorylation which alters the intercellular junction and increases intestinal permeability with consequent intestinal damage. Metronidazole diminishes the inflammation induced by indomethacin but the mechanisms remain speculative. A direct effect on luminal bacteria has traditionally been thought to account for the protective effect of metronidazole. However, a protective effect of metronidazole on mitochondrial oxidative phosphorylation has never been tested. AIMS: To assess the protective effect of metronidazole on mitochondrial uncoupling induced by indomethacin and also on the increased intestinal permeability and macroscopic damage. MATERIAL AND METHODS: The protective effect of metronidazole was evaluated in rats given indomethacin; a macroscopic score was devised to quantify intestinal lesions, and intestinal permeability was measured by means of (51)Cr-ethylenediaminetetraacetic acid. The protective effect of metronidazole against mitochondrial uncoupling induced by indomethacin was assessed using isolated coupled rat liver mitochondria obtained from rats pretreated with metronidazole or saline. RESULTS: Metronidazole significantly reduced the macroscopic intestinal damage and increase in intestinal permeability induced by indomethacin; furthermore, at the mitochondrial level, it significantly reduced the increase in oxygen consumption in state 4 induced by indomethacin and caused less reduction of the respiratory control rate. CONCLUSION: Our study confirmed the beneficial effects of metronidazole on intestinal damage and intestinal permeability, and demonstrated, for the first time, a direct protective effect of metronidazole on uncoupling of mitochondrial oxidative phosphorylation caused by NSAIDs.     

Effect of endotoxin, dobutamine and dopamine on muscle mitochondrial respiration in vitro

INTRODUCTION: Mitochondrial respiration is impaired during endotoxemia. While catecholamines are frequently used in sepsis, their effects on mitochondrial function are controversial. We assessed effects of dobutamine and dopamine endotoxin on isolated muscle mitochondria. MATERIALS AND METHODS: Sternocleidomastoid muscle mitochondria were isolated from six anesthetized pigs. Each sample was divided into six different groups. Three groups were incubated with endotoxin, three with vehicle. After 1 h, dopamine and dobutamine at final concentrations of 100 microM were added to the vehicle and endotoxin groups. After 2 h, state 3 and 4 respiration rates were determined for all mitochondrial complexes. Oxygen consumption was determined with a Clark-type electrode. RESULTS: Endotoxin increased glutamate-dependent state 4 respiration from 9.3 +/- 3.6 to 31.9 +/- 9.1 (P = 0.001) without affecting state 3 respiration. This reduced the efficiency of mitochondrial respiration (RCR; state 3/state 4, 9.9 +/- 1.9 versus 3.6 +/- 0.6; P < 0.001). The other complexes were unaffected. Catecholamine partially restored the endotoxin-induced increase in complex I state 4 respiration rate (31.9 +/- 9.1 versus 17.1 +/- 6.4 and 20.1 +/- 12.2) after dopamine and dobutamine, respectively (P = 0.007), and enhanced the ADP:O ratio (P = 0.033). CONCLUSIONS: Dopamine and dobutamine enhanced the efficiency of mitochondrial respiration after short-term endotoxin exposure.     

A high fat diet increases mitochondrial fatty acid oxidation and uncoupling to decrease efficiency in rat heart

Elevated levels of cardiac mitochondrial uncoupling protein 3 (UCP3) and decreased cardiac efficiency (hydraulic power/oxygen consumption) with abnormal cardiac function occur in obese, diabetic mice. To determine whether cardiac mitochondrial uncoupling occurs in non-genetic obesity, we fed rats a high fat diet (55% kcal from fat) or standard laboratory chow (7% kcal from fat) for 3 weeks, after which we measured cardiac function in vivo using cine MRI, efficiency in isolated working hearts and respiration rates and ADP/O ratios in isolated interfibrillar mitochondria; also, measured were medium chain acyl-CoA dehydrogenase (MCAD) and citrate synthase activities plus uncoupling protein 3 (UCP3), mitochondrial thioesterase 1 (MTE-1), adenine nucleotide translocase (ANT) and ATP synthase protein levels. We found that in vivo cardiac function was the same for all rats, yet oxygen consumption was 19% higher in high fat-fed rat hearts, therefore, efficiency was 21% lower than in controls. We found that mitochondrial fatty acid oxidation rates were 25% higher, and MCAD activity was 23% higher, in hearts from rats fed the high fat diet when compared with controls. Mitochondria from high fat-fed rat hearts had lower ADP/O ratios than controls, indicating increased respiratory uncoupling, which was ameliorated by GDP, a UCP3 inhibitor. Mitochondrial UCP3 and MTE-1 levels were both increased by 20% in high fat-fed rat hearts when compared with controls, with no significant change in ATP synthase or ANT levels, or citrate synthase activity. We conclude that increased cardiac oxygen utilisation, and thereby decreased cardiac efficiency, occurs in non-genetic obesity, which is associated with increased mitochondrial uncoupling due to elevated UCP3 and MTE-1 levels.     

<Emphasis Type="SmallCaps">d</Emphasis>-Galactose toxicity in mice is associated with mitochondrial dysfunction: protecting effects of mitochondrial nutrient R-alpha-lipoic acid

d-Galactose (d-gal) -induced aging models in Drosophila, houseflies, mice and rats have been widely used; however, the underlying mechanisms are poorly understood. To investigate the involvement of mitochondrial dysfunction of d-gal, mitochondrial function was examined in the brain and liver of C57BL/6J mice, subjected to a treatment of d-gal with or without a concomitant treatment with a mitochondrial nutrient, R-alpha-lipoic acid (LA). d-Gal treatment induced a significant decrease in succinate-linked respiratory control ratio (RCR) and ADP/O ratio in the liver and brain, and also a significant increase in the maximum velocity (Vmax) and substrate binding affinity (Km) of complex II in the liver. LA treatment to d-gal-injected animals restored mitochondrial RCR in both brain and liver, ADP/O and Km of complex II in the liver. These results suggest LA is effective in delaying d-gal toxicity by ameliorating mitochondrial dysfunction.     

Reversible uncoupling of oxidative phosphorylation at low oxygen tension.

The stoichiometry of oxidative phosphorylation at low oxygen tension (less than 3 torr; O2 less than 5 microM) has been measured in rat liver mitochondria. In a steady-state model in which respiration rate was experimentally controlled by either oxygen or substrate (succinate) limitation, flux-dependent variation in the phosphorylation efficiency (P/O ratio) of stimulated mitochondrial respiration was evaluated. P/O ratio remained constant over a wide range of respiration rates in mitochondria limited only by substrate availability. In contrast, oxygen-limited mitochondria demonstrated a continuous decline in P/O ratio as respiration was increasingly restricted. Significant differences in the two test conditions were demonstrated throughout the range of analysis. The effect of oxygen limitation on phosphorylation efficiency was shown to be completely reversed by restoring zero-order kinetics associated with high oxygen tension. These findings are discussed in regard to a proposed uncoupling of mitochondrial coupling site II at low oxygen tension arising as a consequence of energy-dissipating electron flux through the ubiquinone-cytochrome b-c1 region of the respiratory chain (complex III).     

Mitochondrial respiratory control is lost during growth factor deprivation

The ability of cells to maintain a bioenergetically favorable ATP/ADP ratio confers a tight balance between cellular events that consume ATP and the rate of ATP production. However, after growth factor withdrawal, the cellular ATP/ADP ratio declines. To investigate these changes, mitochondria from growth factor-deprived cells isolated before the onset of apoptosis were characterized in vitro. Mitochondria from growth factor-deprived cells have lost their ability to undergo matrix condensation in response to ADP, which is accompanied by a failure to perform ADP-coupled respiration. At the time of analysis, mitochondria from growth factor-deprived cells were not depleted of cytochrome c and cytochrome c-dependent respiration was unaffected, demonstrating that the inhibition of the respiratory rate is not due to loss of cytochrome c. Agents that disrupt the mitochondrial outer membrane, such as digitonin, or maintain outer membrane exchange of adenine nucleotide, such as Bcl-x(L), restored ADP-dependent control of mitochondrial respiration. Together, these data suggest that the regulation of mitochondrial outer membrane permeability contributes to respiratory control.     

Effect of adrenochrome on adenine nucleotides and mitochondrial oxidative phosphorylation in rat heart

Effects of adrenochrome, an oxidation product of epinephrine, on myocardial energy production were investigated by studying changes in adenine nucleotide content and mitochondrial oxidative phosphorylation activities in the isolated rat heart. Perfusion of the heart with 50 mg/L adrenochrome induced a marked decline in contractile force within 5 min and this was associated with a rapid decline in the myocardial ATP/AMP ratio. A significant decrease in ATP and ATP/ADP ratio as well as a significant increase in ADP and AMP content was observed at 10 min of perfusion with adrenochrome. Furthermore, mitochondrial oxidative phosphorylation activities were unchanged except that an increase in state 4 respiration and a decrease in RCI value were seen in the heart perfused with adrenochrome for 10 min. Autoradiography of the sections from hearts perfused with 14C-adrenochrome revealed the localization of a significant amount of radioactivity on mitochondria. Adrenochrome at concentrations of 20 mg/L or higher was found to inhibit the oxidative phosphorylation activities of heart mitochondria under in vitro conditions. The depressant effects of adrenochrome on mitochondrial oxidative phosphorylation were additive to those seen with calcium. These data suggest that adrenochrome in the presence of excess calcium in the myocardial cell may impair the process of energy production in mitochondria and this may result in contractile failure of hearts exposed to this cardiotoxic metabolite of epinephrine.     

Age-related alterations in liver mitochondrial bioenergetics of diabetic Goto-Kakizaki rats

Type 2 diabetes mellitus is one of the most common chronic metabolic diseases in man. Due to long-term complications of the disease, severely decreasing the quality of life of diabetic patients, early interventions to obviate the risk of complications are of major importance. Therefore, diabetic animal models are of major importance in research for interventional treatment of type 2 diabetes. In this work we investigated the possible alterations in mitochondrial energetic metabolism of Goto-Kakizaki (GK) rats during the progression of the disease, since glucose metabolism is closely related to intracellular ATP content. For that reason, respiratory indexes (state 4, state 3, RCR and ADP/O) were evaluated either in the presence of NAD- or FAD-linked substrates (glutamate + malate and succinate, respectively) in mitochondrial preparations of GK and control rats with 8, 12, 26 and 52 weeks of age. Until the age of 1 year (52 weeks) we found no impairment of mitochondrial respiratory indexes both in the presence of glutamate + malate and succinate. In conclusion, this study indicates that GK rat is a good model for studying the initial events of diabetes, since it presents no impairment of liver mitochondrial functions during the first year of life, contrasting clearly with pharmacological induced diabetes. Received: 7 May 1999 / Accepted in revised form: 17 December 1999     

Bioenergetics at low oxygen: dependence of respiration and phosphorylation on oxygen and adenosine diphosphate supply.

Oxygen limitation is generally considered as impairment of mitochondrial respiration under hypoxia and ischemia. Low intracellular oxygen levels under normoxia, however, imply mild oxygen limitation, provide protection from oxidative stress, and result from economical strategies for oxygen transport through the respiratory cascade to cytochrome c oxidase. Both perspectives relate to the critical oxygen pressure, which inhibits mitochondrial respiration. Based on methodological considerations of oxygen kinetics and a presentation of high-resolution respirometry, mitochondrial oxygen affinities (1/P(50)) are reviewed with particular emphasis on the turnover effect under control of adenosine diphosphate ADP concentration, which increases the P(50) in active states. ADP/O(2) flux ratios are high even under severe oxygen limitation, as demonstrated by calorespirometry. Oxygen limitation reduces the uncoupled respiration observed under control by ADP, as shown by relationships derived between ADP/O(2) flux ratios, respiratory control ratios, and ADP kinetics. Bioenergetics at low oxygen versus oxidative stress must be considered in the context of limitation of maximum aerobic activity, ischemia-reperfusion injury, mitochondrial signalling to apoptosis, and mitochondrial theories of ageing.     

Mitochondrial oxidative phosphorylation in heart from stressed cardiomyopathic hamsters

Stress alone is generally not sufficient to produce serious disease, but stress imposed upon pre-existing disease can contribute to disease progression. To explore this phenomenon, cold-immobilization stress was imposed on young 12.5 month, necrotic phase with small vessel coronary spasm) and older (5 month, quiescent phase, between necrosis and heart failure) cardiomyopathic hamsters. Our hypothesis was that changes in mitochondrial energy processes are involved in stress induced pathology. Polarographic and high performance liquid chromatography (HPLC) techniques were used to measure mitochondrial respiration and oxidative phosphorylation and concentrations of phosphocreatine and adenylates, respectively, in hearts from young and old cardiomyopathic hamsters (stressed and unstressed). No significant differences were found between the young (2.5 month) and old (5 month) age groups in unstressed and stressed healthy hamsters and between young (2.5 month) and old (5 month) unstressed cardiomyopathic hamsters with respect to different parameters of mitochondrial oxidative phosphorylation and with respect to concentration of bioenergetic metabolites, except that ADP concentration was higher in older cardiomyopathic hamsters. Application of stress uncovered differences between young and old cardiomyopathic hamsters: respiration control index was lower and State 4 respiration was higher in young compared to old cardiomyopathic hamsters; whereas the total concentration of ATP was decreased to the same level in both cardiomyopathic groups when compared to control. Mitochondrial oxidative phosphorylation in young cardiomyopathic hamsters was more sensitive to Ca2+, as evidenced by partial uncoupling of respiration and oxidative phosphorylation, than in older cardiomyopathic hamsters and controls. In conclusion, young cardiomyopathic hamsters, i.e. in the necrotic phase of disease, were more susceptible to stress induced changes in mitochondrial oxidative phosphorylation than older cardiomyopathic hamsters and controls.