RESUMO
Inositol hexakisphosphate kinases (IP6Ks) regulate various biological processes. IP6Ks convert IP6 to pyrophosphates such as diphosphoinositol pentakisphosphate (IP7) and bis-diphosphoinositol tetrakisphosphate (IP8). IP7 is produced in mammals by a family of inositol hexakisphosphate kinases, IP6K1, IP6K2, and IP6K3, which have distinct biological functions. The inositol hexakisphosphate kinase 2 (IP6K2) controls cellular apoptosis. To explore roles for IP6K2 in brain function, we elucidated its protein interactome in mouse brain revealing a robust association of IP6K2 with creatine kinase-B (CK-B), a key enzyme in energy homeostasis. Cerebella of IP6K2-deleted mice (IP6K2-knockout [KO]) produced less phosphocreatine and ATP and generated higher levels of reactive oxygen species and protein oxidative damage. In IP6K2-KO mice, mitochondrial dysfunction was associated with impaired expression of the cytochrome-c1 subunit of complex III of the electron transport chain. We reversed some of these effects by combined treatment with N-acetylcysteine and phosphocreatine. These findings establish a role for IP6K2-CK-B interaction in energy homeostasis associated with neuroprotection.
Assuntos
Creatina Quinase/genética , Metabolismo Energético/genética , Fosfotransferases (Aceptor do Grupo Fosfato)/genética , Acetilcisteína/metabolismo , Trifosfato de Adenosina/biossíntese , Animais , Apoptose/genética , Citocromos c1/genética , Complexo III da Cadeia de Transporte de Elétrons/genética , Humanos , Camundongos , Camundongos Knockout , Mitocôndrias/genética , Mitocôndrias/patologia , Fosfocreatina/biossínteseRESUMO
PURPOSE: The goal of this study was to amplify the effects of magnetization exchange between γ-adenosine triphosphate (ATP) and inorganic phosphate (Pi) for evaluation of ATP synthesis rates in human skeletal muscle. METHODS: The strategy works by simultaneously inverting the (31) P resonances of phosphocreatine (PCr) and ATP using a wide bandwidth, adiabatic inversion radiofrequency pulse followed by observing dynamic changes in intensity of the noninverted Pi signal versus the delay time between the inversion and observation pulses. This band inversion technique significantly delays recovery of γ-ATP magnetization; consequently, the exchange reaction, Pi â γ-ATP, is readily detected and easily analyzed. RESULTS: The ATP synthesis rate measured from high-quality spectral data using this method was 0.073 ± 0.011 s(-1) in resting human skeletal muscle (N = 10). The T1 of Pi was 6.93 ± 1.90 s, consistent with the intrinsic T1 of Pi at this field. The apparent T1 of γ-ATP was 4.07 ± 0.32 s, about two-fold longer than its intrinsic T1 due to storage of magnetization in PCr. CONCLUSION: Band inversion provides an effective method to amplify the effects of magnetization transfer between γ-ATP and Pi. The resulting data can be easily analyzed to obtain the ATP synthesis rate using a two-site exchange model.
Assuntos
Trifosfato de Adenosina/biossíntese , Algoritmos , Espectroscopia de Ressonância Magnética/métodos , Imagem Molecular/métodos , Fosfocreatina/biossíntese , Adulto , Feminino , Humanos , Masculino , Músculo Esquelético , Radioisótopos de Fósforo/farmacocinética , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
To investigate the high-energy phosphate metabolism by (31) P-nuclear magnetic resonance spectroscopy during off-transition of exercise in different muscle groups, such as calf muscles and biceps femoris muscles, seven male long-distance runners (LDR) and nine untrained males (UT) performed both submaximal constant and incremental exercises. The relative exercise intensity was set at 60% of the maximal work rate (60%W max) during both knee flexion and plantar flexion submaximal constant load exercises. The relative areas under the inorganic phosphate (Pi ) and phosphocreatine (PCr) peaks were determined. During the 5-min recovery following the 60%W max, the time constant for the PCr off-kinetics was significantly faster in the plantar flexion (LDR: 17.3 ± 3.6 s, UT: 26.7 ± 6.7 s) than in the knee flexion (LDR: 29.7 ± 4.7 s, UT: 42.7 ± 2.8 s, P < 0.05). In addition, a significantly faster PCr off-kinetics was observed in LDR than in UT for both exercises. The ratio of Pi to PCr (Pi /PCr) during exercise was significantly lower during the plantar flexion than during the knee flexion (P < 0.01). These findings indicated that the calf muscles had relatively higher potential for oxidative capacity than that of biceps femoris muscles with an association of training status.
Assuntos
Exercício Físico/fisiologia , Músculo Esquelético/metabolismo , Consumo de Oxigênio/fisiologia , Fosfocreatina/biossíntese , Corrida/fisiologia , Trifosfato de Adenosina/metabolismo , Análise de Variância , Metabolismo Energético/fisiologia , Humanos , Perna (Membro)/fisiologia , Espectroscopia de Ressonância Magnética/métodos , Masculino , Contração Muscular/fisiologia , Adulto JovemRESUMO
Team sports are increasingly popular, with millions of participants worldwide. Athletes engaged in these sports are required to repeatedly produce skilful actions and maximal or near-maximal efforts (eg, accelerations, changes in pace and direction, sprints, jumps and kicks), interspersed with brief recovery intervals (consisting of rest or low-intensity to moderate-intensity activity), over an extended period of time (1-2 h). While performance in most team sports is dominated by technical and tactical proficiencies, successful team-sport athletes must also have highly-developed, specific, physical capacities. Much effort goes into designing training programmes to improve these physical capacities, with expected benefits for team-sport performance. Recently, some team sports have introduced altitude training in the belief that it can further enhance team-sport physical performance. Until now, however, there is little published evidence showing improved team-sport performance following altitude training, despite the often considerable expense involved. In the absence of such studies, this review will identify important determinants of team-sport physical performance that may be improved by altitude training, with potential benefits for team-sport performance. These determinants can be broadly described as factors that enhance either sprint performance or the ability to recover from maximal or near-maximal efforts. There is some evidence that some of these physical capacities may be enhanced by altitude training, but further research is required to verify that these adaptations occur, that they are greater than what could be achieved by appropriate sea-level training and that they translate to improved team-sport performance.
Assuntos
Aclimatação/fisiologia , Altitude , Desempenho Atlético/fisiologia , Trifosfato de Adenosina/metabolismo , Soluções Tampão , Metabolismo Energético/fisiologia , Processos Grupais , Humanos , Força Muscular/fisiologia , Músculo Esquelético/fisiologia , Consumo de Oxigênio/fisiologia , Fosfocreatina/biossíntese , Desempenho Psicomotor/fisiologia , Corrida/fisiologiaRESUMO
To better understand the mechanisms underlying the pulmonary O(2) uptake (V(O(2P))) slow component during high-intensity exercise, we used (31)P magnetic resonance spectroscopy, gas exchange, surface electromyography and near-infrared spectroscopy measurements to examine the potential relationship between the slow components of V(O(2P)) and phosphocreatine (PCr), muscle recruitment and tissue oxygenation in endurance-trained athletes and sedentary subjects. Specifically, six endurance-trained and seven sedentary subjects performed a dynamic high-intensity exercise protocol during 6 min at an exercise intensity corresponding to 35-40% of knee-extensor maximal voluntary contraction. The slow component of V(O(2P))(117 ± 60 ml min(-1), i.e. 20 ± 10% of the total response) was associated with a paradoxical PCr resynthesis in endurance-trained athletes (-0.90 ± 1.27 mm, i.e. -12 ± 16% of the total response). Meanwhile, oxygenated haemoglobin increased throughout the second part of exercise and was significantly higher at the end of exercise compared with the value at 120 s (P < 0.05), whereas the integrated EMG was not significantly changed throughout exercise. In sedentary subjects, a slow component was simultaneously observed for V(O(2P)) and [PCr] time-dependent changes (208 ± 14 ml min(-1), i.e. 38 ± 18% of the total V(O(2P))response, and 1.82 ± 1.39 mm, i.e. 16 ± 13% of the total [PCr] response), but the corresponding absolute or relative amplitudes were not correlated. The integrated EMG was significantly increased throughout exercise in sedentary subjects. Taken together, our results challenge the hypothesis of a mechanistic link between [PCr] and V(O(2P)) slow components and demonstrate that, as a result of a tighter metabolic control and increased O(2) availability, the [PCr] slow component can be minimized in endurance-trained athletes while the V(O(2P)) slow component occurs.
Assuntos
Exercício Físico/fisiologia , Consumo de Oxigênio/fisiologia , Fosfocreatina/fisiologia , Adulto , Eletromiografia , Feminino , Humanos , Joelho/fisiologia , Espectroscopia de Ressonância Magnética , Masculino , Contração Muscular/fisiologia , Músculo Esquelético/fisiologia , Fosfocreatina/biossíntese , Resistência Física/fisiologia , Troca Gasosa Pulmonar/fisiologia , Comportamento Sedentário , Adulto JovemRESUMO
Organisation of mitochondrial metabolism is a quintessential example of a complex dissipative system which can display dynamic instabilities. Several findings have indicated that the conditions inducing instabilities are within the physiological range and that mild perturbations could elicit oscillations. Different mathematical models have been put forth in order to explain the genesis of oscillations in energy metabolism. One model considers mitochondria as an organised network of oscillators and indicates that communication between mitochondria involves mitochondrial reactive oxygen species (ROS) production acting as synchronisers of the energy status of the whole population of mitochondria. An alternative model proposes that extramitochondrial pH variations could lead to mitochondrial oscillations. Oscillatory phenomena in energy metabolism have also been investigated in vivo on the basis of 31P magnetic resonance spectroscopy (MRS) measurements of phosphocreatine post-exercise recovery in human and animal skeletal muscle. The corresponding results provide experimental evidences about the role exerted by cytosolic pH on oscillations. Finally a new simple non-linear mathematical model describing the overall chemical reaction of phosphocreatine recovery predicting oscillatory recovery pattern under certain experimental conditions is presented and discussed in the light of the experimental results reported so far.
Assuntos
Metabolismo Energético , Animais , Humanos , Mitocôndrias/metabolismo , Modelos Biológicos , Músculo Esquelético/metabolismo , Fosfocreatina/biossínteseRESUMO
The pleiotropic effects of creatine (Cr) are based mostly on the functions of the enzyme creatine kinase (CK) and its high-energy product phosphocreatine (PCr). Multidisciplinary studies have established molecular, cellular, organ and somatic functions of the CK/PCr system, in particular for cells and tissues with high and intermittent energy fluctuations. These studies include tissue-specific expression and subcellular localization of CK isoforms, high-resolution molecular structures and structure-function relationships, transgenic CK abrogation and reverse genetic approaches. Three energy-related physiological principles emerge, namely that the CK/PCr systems functions as (a) an immediately available temporal energy buffer, (b) a spatial energy buffer or intracellular energy transport system (the CK/PCr energy shuttle or circuit) and (c) a metabolic regulator. The CK/PCr energy shuttle connects sites of ATP production (glycolysis and mitochondrial oxidative phosphorylation) with subcellular sites of ATP utilization (ATPases). Thus, diffusion limitations of ADP and ATP are overcome by PCr/Cr shuttling, as most clearly seen in polar cells such as spermatozoa, retina photoreceptor cells and sensory hair bundles of the inner ear. The CK/PCr system relies on the close exchange of substrates and products between CK isoforms and ATP-generating or -consuming processes. Mitochondrial CK in the mitochondrial outer compartment, for example, is tightly coupled to ATP export via adenine nucleotide transporter or carrier (ANT) and thus ATP-synthesis and respiratory chain activity, releasing PCr into the cytosol. This coupling also reduces formation of reactive oxygen species (ROS) and inhibits mitochondrial permeability transition, an early event in apoptosis. Cr itself may also act as a direct and/or indirect anti-oxidant, while PCr can interact with and protect cellular membranes. Collectively, these factors may well explain the beneficial effects of Cr supplementation. The stimulating effects of Cr for muscle and bone growth and maintenance, and especially in neuroprotection, are now recognized and the first clinical studies are underway. Novel socio-economically relevant applications of Cr supplementation are emerging, e.g. for senior people, intensive care units and dialysis patients, who are notoriously Cr-depleted. Also, Cr will likely be beneficial for the healthy development of premature infants, who after separation from the placenta depend on external Cr. Cr supplementation of pregnant and lactating women, as well as of babies and infants are likely to be of benefit for child development. Last but not least, Cr harbours a global ecological potential as an additive for animal feed, replacing meat- and fish meal for animal (poultry and swine) and fish aqua farming. This may help to alleviate human starvation and at the same time prevent over-fishing of oceans.
Assuntos
Creatina Quinase/metabolismo , Creatina/metabolismo , Animais , Humanos , Fosfocreatina/biossíntese , Fosfocreatina/metabolismoRESUMO
The aim of this study was to measure energy fluxes from mitochondria in isolated permeabilized cardiomyocytes. Respiration of permeabilized cardiomyocytes and mitochondrial membrane potential were measured in presence of MgATP, pyruvate kinase - phosphoenolpyruvate and creatine. ATP and phosphocreatine concentrations in medium surrounding cardiomyocytes were determined. While ATP concentration did not change in time, mitochondria effectively produced phosphocreatine (PCr) with PCr/O(2) ratio equal to 5.68 +/- 0.14. Addition of heterodimeric tubulin to isolated mitochondria was found to increase apparent Km for exogenous ADP from 11 +/- 2 microM to 330 +/- 47 microM, but creatine again decreased it to 23 +/- 6 microM. These results show directly that under physiological conditions the major energy carrier from mitochondria into cytoplasm is PCr, produced by mitochondrial creatine kinase (MtCK), which functional coupling to adenine nucleotide translocase is enhanced by selective limitation of permeability of mitochondrial outer membrane within supercomplex ATP Synthasome-MtCK-VDAC-tubulin, Mitochondrial Interactosome.
Assuntos
Metabolismo Energético/fisiologia , Potencial da Membrana Mitocondrial/fisiologia , Mitocôndrias Cardíacas/fisiologia , Trifosfato de Adenosina/metabolismo , Animais , Respiração Celular/fisiologia , Cromatografia Líquida de Alta Pressão , Creatina Quinase Mitocondrial/metabolismo , Creatinina/metabolismo , Modelos Biológicos , Consumo de Oxigênio/fisiologia , Fosfocreatina/biossíntese , Fosfoenolpiruvato/metabolismo , Piruvato Quinase/metabolismo , Ratos , Tubulina (Proteína)/metabolismoRESUMO
Beetroot juice contains high levels of inorganic nitrate (NO3-) and its intake has proved effective at increasing blood nitric oxide (NO) concentrations. Given the effects of NO in promoting vasodilation and blood flow with beneficial impacts on muscle contraction, several studies have detected an ergogenic effect of beetroot juice supplementation on exercise efforts with high oxidative energy metabolism demands. However, only a scarce yet growing number of investigations have sought to assess the effects of this supplement on performance at high-intensity exercise. Here we review the few studies that have addressed this issue. The databases Dialnet, Elsevier, Medline, Pubmed and Web of Science were searched for articles in English, Portuguese and Spanish published from 2010 to March 31 to 2017 using the keywords: beet or beetroot or nitrate or nitrite and supplement or supplementation or nutrition or "sport nutrition" and exercise or sport or "physical activity" or effort or athlete. Nine articles fulfilling the inclusion criteria were identified. Results indicate that beetroot juice given as a single dose or over a few days may improve performance at intermittent, high-intensity efforts with short rest periods. The improvements observed were attributed to faster phosphocreatine resynthesis which could delay its depletion during repetitive exercise efforts. In addition, beetroot juice supplementation could improve muscle power output via a mechanism involving a faster muscle shortening velocity. The findings of some studies also suggested improved indicators of muscular fatigue, though the mechanism involved in this effect remains unclear.
Assuntos
Desempenho Atlético , Beta vulgaris , Suplementos Nutricionais , Sucos de Frutas e Vegetais , Treinamento Intervalado de Alta Intensidade , Metabolismo Energético , Humanos , Nitratos/metabolismo , Nitritos/metabolismo , Fosfocreatina/biossíntese , Fenômenos Fisiológicos da Nutrição EsportivaRESUMO
We used phosphorus nuclear magnetic resonance spectroscopy (31P-NMR) to probe the cellular events in contracting muscle that initiate the reflex stimulation of sympathetic outflow during exercise. In conscious humans, we performed 31P-NMR on exercising forearm muscle and simultaneously recorded muscle sympathetic nerve activity (MSNA) with microelectrodes in the peroneal nerve to determine if the activation of MSNA is coupled to muscle pH, an index of glycolysis, or to the concentrations (II) of inorganic phosphate (Pi) and adenosine diphosphate (ADP) which are modulators of mitochondrial respiration. During both static and rhythmic handgrip, the onset of sympathetic activation in resting muscle coincided with the development of cellular acidification in active muscle. Furthermore, increases in MSNA were correlated closely with decreases in intracellular pH but dissociated from changes in phosphocreatine [( PCr]), [Pi], and [ADP]. The principal new conclusion is that activation of muscle sympathetic outflow during exercise in humans is coupled to the cellular accumulation of protons in contracting muscle.
Assuntos
Eletrofisiologia , Exercício Físico , Músculos/inervação , Sistema Nervoso Simpático/fisiologia , Difosfato de Adenosina/biossíntese , Adulto , Feminino , Humanos , Concentração de Íons de Hidrogênio , Espectroscopia de Ressonância Magnética , Masculino , Contração Muscular , Músculos/citologia , Músculos/metabolismo , Fosfatos/biossíntese , Fosfocreatina/biossínteseRESUMO
Phosphocreatine (PCr) resynthesis rate following intense anoxic contraction can be used as a sensitive index of in vivo mitochondrial function. We examined the effect of a diet-induced increase in uncoupling protein 3 (UCP3) expression on postexercise PCr resynthesis in skeletal muscle. Nine healthy male volunteers undertook 20 one-legged maximal voluntary contractions with limb blood flow occluded to deplete muscle PCr stores. Exercise was performed following 7 days consumption of low-fat (LF) or high-fat (HF) diets. Immediately following exercise, blood flow was reinstated, and muscle was sampled after 20, 60, and 120 seconds of recovery. Mitochondrial coupling was assessed by determining the rate of PCr resynthesis during recovery. The HF diet increased UCP3 protein content by approximately 44% compared with the LF diet. However, this HF diet-induced increase in UCP3 expression was not associated with any changes in the rate of muscle PCr resynthesis during conditions of maximal flux through oxidative phosphorylation. Muscle acetylcarnitine, free-creatine, and lactate concentrations during recovery were unaffected by the HF diet. Taken together, our findings demonstrate that increasing muscle UCP3 expression does not diminish the rate of PCr resynthesis, allowing us to conclude that the primary role of UCP3 in humans is not uncoupling.
Assuntos
Proteínas de Transporte/metabolismo , Mitocôndrias Musculares/metabolismo , Músculo Esquelético/metabolismo , Adulto , Creatina/metabolismo , Gorduras na Dieta/administração & dosagem , Ácidos Graxos/metabolismo , Humanos , Canais Iônicos , Ácido Láctico/metabolismo , Masculino , Proteínas Mitocondriais , Contração Muscular/fisiologia , Fosforilação Oxidativa , Fosfocreatina/biossíntese , ATPases Translocadoras de Prótons/metabolismo , Desacopladores/metabolismo , Proteína Desacopladora 3RESUMO
The basis for skeletal muscle dysfunction in phosphate-deficient patients and animals is not known, but it is hypothesized that intracellular phosphate deficiency leads to a defect in ATP synthesis. To test this hypothesis, changes in muscle function and nucleotide metabolism were studied in an animal model of hypophosphatemia. Mice were made hypophosphatemic through restriction of dietary phosphate intake. Gastrocnemius function was assessed in situ by recording isometric tension developed after stimulation of the nerve innervating this muscle. Changes in purine nucleotide, nucleoside, and base content of the muscle were quantitated at several time points during stimulation and recovery. Serum concentration and skeletal muscle content of phosphorous are reduced by 55 and 45%, respectively, in the dietary restricted animals. The gastrocnemius muscle of the phosphate-deficient mice fatigues more rapidly compared with control mice. ATP and creatine phosphate content fall to a comparable extent during fatigue in the muscle from both groups of animals; AMP, inosine, and hypoxanthine (indices of ATP catabolism) appear in higher concentration in the muscle of phosphate-deficient animals. Since total ATP use in contracting muscle is closely linked to total developed tension, we conclude that the comparable drop in ATP content in association with a more rapid loss of tension is best explained by a slower rate of ATP synthesis in the muscle of phosphate-deficient animals. During the period of recovery after muscle stimulation, ATP use for contraction is minimal, since the muscle is at rest. In the recovery period, ATP content returns to resting levels more slowly in the phosphate-deficient than in the control animals. In association with the slower rate of ATP repletion, the precursors inosine monophosphate and AMP remain elevated for a longer period of time in the muscle of phosphate-deficient animals. The slower rate of ATP repletion correlates with delayed return of normal muscle contractility in the phosphate-deficient mice. These studies suggest that the slower rate of repletion of the ATP pool may be the consequence of a slower rate of ATP synthesis and this is in part responsible for the delayed recovery of normal muscle contractility.
Assuntos
Trifosfato de Adenosina/biossíntese , Modelos Animais de Doenças , Músculos/metabolismo , Fosfatos/sangue , Trifosfato de Adenosina/análise , Animais , Composição de Bases , Inosina Monofosfato/análise , Inosina Monofosfato/biossíntese , Camundongos , Camundongos Endogâmicos C57BL , Contração Muscular , Músculos/análise , Músculos/fisiologia , Fosfocreatina/análise , Fosfocreatina/biossíntese , Fósforo/análise , Fósforo/sangueRESUMO
Skeletal muscle mitochondrial oxidative capacity declines with age and negatively affects walking performance, but the mechanism for this association is not fully clear. We tested the hypothesis that impaired oxidative capacity affects muscle performance and, through this mechanism, has a negative effect on walking speed. Muscle mitochondrial oxidative capacity was measured by in vivo phosphorus magnetic resonance spectroscopy as the postexercise phosphocreatine resynthesis rate, kPCr , in 326 participants (154 men), aged 24-97 years (mean 71), in the Baltimore Longitudinal Study of Aging. Muscle strength and quality were determined by knee extension isokinetic strength, and the ratio of knee extension strength to thigh muscle cross-sectional area derived from computed topography, respectively. Four walking tasks were evaluated: a usual pace over 6 m and for 150 s, and a rapid pace over 6 m and 400 m. In multivariate linear regression analyses, kPCr was associated with muscle strength (ß = 0.140, P = 0.007) and muscle quality (ß = 0.127, P = 0.022), independent of age, sex, height, and weight; muscle strength was also a significant independent correlate of walking speed (P < 0.02 for all tasks) and in a formal mediation analysis significantly attenuated the association between kPCr and three of four walking tasks (18-29% reduction in ß for kPCr ). This is the first demonstration in human adults that mitochondrial function affects muscle strength and that inefficiency in muscle bioenergetics partially accounts for differences in mobility through this mechanism.
Assuntos
Envelhecimento/metabolismo , Metabolismo Energético/fisiologia , Mitocôndrias/metabolismo , Força Muscular/fisiologia , Músculo Esquelético/metabolismo , Atrofia Muscular/fisiopatologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Envelhecimento/patologia , Baltimore , Estudos Transversais , Feminino , Humanos , Estudos Longitudinais , Masculino , Pessoa de Meia-Idade , Mitocôndrias/patologia , Músculo Esquelético/fisiopatologia , Atrofia Muscular/diagnóstico , Atrofia Muscular/metabolismo , Fosfocreatina/biossíntese , CaminhadaRESUMO
Two human small cell lung cancer tumor lines, maintained as solid tumor xenografts on nude mice and as in vitro cell cultures, were studied by in vivo 31P magnetic resonance spectroscopy and by biochemical analysis of extracts of solid tumors and cell cultures. The tumor lines CPH SCCL 54A and CPH SCCL 54B are subpopulations from the same tumor. In solid tumors (n = 125), the ATP/Pi ratio was greater in 54A than in 54B. This was due to a higher ATP level in 54A, whereas there was no difference in Pi, ADP, and AMP. A decrease in ATP/Pi during growth was caused by a decline in ATP, whereas Pi remained unchanged. Small amounts of phosphocreatine were found in the xenografts and in tumor extracts, but not in the cell extracts; correspondingly, there was a low creatine kinase activity in solid tumors and no activity in the cell cultures. Thus, the phosphocreatine content of the solid tumors originated from the stroma. A difference in ATP content between 54A and 54B was also found in cell cultures; hence, the metabolic difference is an intrinsic quality of the malignant cells and is not caused by the host system.
Assuntos
Carcinoma de Células Pequenas/metabolismo , Metabolismo Energético , Neoplasias Pulmonares/metabolismo , Difosfato de Adenosina/análise , Monofosfato de Adenosina/análise , Trifosfato de Adenosina/metabolismo , Animais , Humanos , Espectroscopia de Ressonância Magnética , Camundongos , Camundongos Nus , Transplante de Neoplasias , Fosfocreatina/biossíntese , Fósforo/análise , Transplante Heterólogo , Células Tumorais CultivadasRESUMO
For the first time, a probability approach was used to describe heart mitochondrial respiration in the medium with ATP, Cr and PCr but without ADP. Respiring mitochondria were considered as a three-component system, including (1) oxidative phosphorylation reactions which provide stable ATP concentration in the mitochondrial matrix; (2) adenine nucleotide translocase, which provides exchange transfer of matrix ATP for outside creatine kinase-supplied ADP when both substrates are simultaneously bound to translocase and (3) creatine kinase, starting these reactions when activated by the substrates from medium. The specific feature of this system is a close proximity of creatine kinase and translocase molecules. This results in high probability of direct activation of translocase by creatine kinase-derived ADP without its leak into the medium. In turn, the activated translocase with the same high probability directly provides creatine kinase with matrix-derived ATP. The catalytic complexes of creatine kinase with ATP from matrix together with those formed from substrates from medium provide high activation of creatine kinase coupled to translocase activation. The considered probabilities were arranged into a mathematical model. The model satisfactorily simulates the experimental data by Jacobus, W.E. and Saks, V.A. ((1982) Arch. Biochem. Biophys. 219, 167-178), who investigated this system in all regimens of functioning. The results suggest the observed kinetic and thermodynamic irregularities in the behavior of structurally-bound creatine kinase as a direct consequence of its tight coupling to translocase.
Assuntos
Creatina Quinase/metabolismo , Mitocôndrias Cardíacas/metabolismo , Translocases Mitocondriais de ADP e ATP/metabolismo , Fosfocreatina/biossíntese , Trifosfato de Adenosina/metabolismo , Animais , Creatina/metabolismo , Cinética , Modelos Teóricos , Fosforilação Oxidativa , Fosfocreatina/metabolismoRESUMO
Net phosphocreatine (PCr) resynthesis during muscle contraction is a paradoxical phenomenon because it occurs under conditions of high energy demand. The metabolic underpinnings of this phenomenon were analyzed non-invasively using 31P-magnetic resonance spectroscopy in rat gastrocnemius muscle (n=11) electrically stimulated (7.6 Hz, 6 min duration) in situ under ischemic and normoxic conditions. During ischemic stimulation, [PCr] initially fell to a steady state (9+/-5% of resting concentration) which was maintained for the last 5 min of stimulation, whereas isometric force production decreased to a non-measurable level beyond 3 min. Throughout normoxic stimulation, [PCr] and force production declined to a steady state after respectively 1 min (5+/-3% of resting concentration) and 3.25 min (21+/-8% of initial value) of stimulation. Contrary to the observations under ischemia, a paradoxical net PCr resynthesis was recorded during the last 2 min of normoxic stimulation and was not accompanied by any improvement in force production. These results demonstrate that the paradoxical net PCr resynthesis recorded in contracting muscle relies exclusively on oxidative energy production and could occur in inactivated fibers, similarly to PCr resynthesis during post-exercise recovery.
Assuntos
Contração Muscular , Músculo Esquelético/metabolismo , Fosfocreatina/biossíntese , Trifosfato de Adenosina/metabolismo , Anaerobiose , Animais , Estimulação Elétrica , Metabolismo Energético , Glicólise , Membro Posterior , Concentração de Íons de Hidrogênio , Contração Isométrica , Espectroscopia de Ressonância Magnética , Masculino , Músculo Esquelético/química , Fosforilação Oxidativa , Fosfocreatina/química , Ratos , Ratos Wistar , Fatores de TempoRESUMO
Phosphocreatine production ctalyzed by a cytosolic fraction from cardiac muscle containing all glycolytic enzymes and creatine kinase in a soluble form has been studied in the presence of creatine, adenine nucleotides and different glycolytic intermedites as substrates. Glycolytic depletion of glucose, fructose 1,6bis(phosphate) and phosphoenolpyruvate to lactte was coupled to efficient phosphocreatine production. The molar ratio of phosphocreatine to lactate produced was close to 2.0 when fructose 1,6bis(phosphate) was used as substrate and 1.0 with phosphoenolpyruvate. In these processes the creatine kinase reaction was not the rate-limiting step: themass action ratio of the creatine kinase reaction was very close to its equilibrium value and the maximal rate of the forward creatine kinase reaction exceeded that of glycolytic flux by about 6-fold when fructose 1,6-bis(phosphate) was used as a substrate. Therefore, the creatine kinase raction was continuously in the state of quasi-equilibrium and the efficient syntheses of phosphocreatine observed is a result of constant removal of ADP by the glycolytic system at an almost unchanged level of ATP ([ATP]>>[ADP]), this leading to a continuous shift of the creatine kinase equilibrium position. When phosphocreatine was added initially at concentrations of 5---15 mM the rate of the coupled creatine kinase and glycolytic reactions was very significantly inhibited due to a sharp decrease in the steady-state concentration of ADP. Therefore, under conditions of effective phosphocreatine production in heart mitochondria, which maintain a high phosphocreatine: creatine ratio in the myoplasm in vivo, the glycolytic flux may be suppressed due to limited availability of ADP restricted by the creatine kinase system. The possible physiological role of the control of the glycolytic flux by the creatine kinase system is discussed.
Assuntos
Citosol/metabolismo , Fosfocreatina/biossíntese , Creatina Quinase/metabolismo , Frutosedifosfatos/metabolismo , Glucose/metabolismo , Glicólise , Cinética , Modelos Biológicos , Miocárdio/citologia , Fosfoenolpiruvato/metabolismo , Piruvato Quinase/metabolismoRESUMO
OBJECTIVES: This study investigated the effects of physical training on skeletal muscle metabolism in patients with chronic heart failure. BACKGROUND: Skeletal muscle metabolic abnormalities in patients with chronic heart failure have been associated with exercise intolerance. Muscle deconditioning is a possible mechanism for the intrinsic skeletal muscle metabolic changes seen in chronic heart failure. METHODS: We used phosphorus-31 nuclear magnetic resonance spectroscopy to study muscle metabolism during exercise in 12 patients with stable ischemic chronic heart failure undergoing 8 weeks of home-based bicycle exercise training in a randomized crossover controlled trial. Changes in muscle pH and concentrations of phosphocreatine and adenosine diphosphate (ADP) were measured in phosphorus-31 spectra of calf muscle obtained at rest, throughout incremental work load plantar flexion until exhaustion and during recovery from exercise. Results were compared with those in 15 age-matched control subjects who performed a single study only. RESULTS: Before training, phosphocreatine depletion, muscle acidification and the increase in ADP during the 1st 4 min of plantar flexion exercise were all increased (p < 0.04) compared with values in control subjects. Training produced an increase (p < 0.002) in incremental plantar flexion exercise tolerance. After training, phosphocreatine depletion and the increase in ADP during exercise were reduced significantly (p < 0.003) at all matched submaximal work loads and at peak exercise, although there was no significant change in the response of muscle pH to exercise. After training, changes in ADP were not significantly different from those in control subjects, although phosphocreatine depletion was still greater (p < 0.05) in trained patients than in control subjects. The phosphocreatine recovery half-time was significantly (p < 0.05) shorter after training, although there was no significant change in the half-time of adenosine diphosphate recovery. In untrained subjects, the initial rate of phosphocreatine resynthesis after exercise (a measure of the rate of oxidative adenosine triphosphate [ATP] synthesis) and the inferred maximal rate of mitochondrial ATP synthesis were reduced compared with rates in control subjects (p < 0.003) and both were significantly increased (p < 0.05) by training, so that they were not significantly different from values in control subjects. CONCLUSIONS: The reduction in phosphocreatine depletion and in the increase in ADP during exercise, and the enhanced rate of phosphocreatine resynthesis in recovery (which is independent of muscle mass) indicate that a substantial correction of the impaired oxidative capacity of skeletal muscle in chronic heart failure can be achieved by exercise training.
Assuntos
Terapia por Exercício , Insuficiência Cardíaca/reabilitação , Músculos/metabolismo , Difosfato de Adenosina/análise , Adulto , Idoso , Débito Cardíaco , Doença Crônica , Tolerância ao Exercício , Insuficiência Cardíaca/metabolismo , Insuficiência Cardíaca/fisiopatologia , Humanos , Masculino , Pessoa de Meia-Idade , Músculos/química , Consumo de Oxigênio , Fosfocreatina/biossíntese , Fosfocreatina/metabolismoRESUMO
AIM: The aim of this study was to investigate the effects of creatine supplementation on performance during the repeated bouts of supramaximal exercise. METHODS: Twenty-three untrained young males participated in the study. A double blind design was used to create the creatine and placebo groups. Wingate test was performed 5 times with 90 g x kg(-1) body weight load with 2-min intervals. Peak power, mean power (MP), fatigue index (FI) were calculated. Capillary blood samples for lactate analysis were taken during the initial rest period and soon after the fifth Wingate test. For 6 days the creatine group (n=12) ingested 5 g creatine monohydrate, the placebo group (n=11) a flavored drink without creatine monohydrate 4 times daily. On the 7th day, the Wingate tests were repeated, as was the 1st day. RESULTS: In the creatine group, MP in the 3rd and 4th Wingate test, in the placebo group FI in the 1st and 2nd Wingate test significantly increased. While the total power output obtained from the five Wingate tests increased 7.6% from 366.3+/-65 W to 394+/-67.1 W, there was no change in the placebo group. CONCLUSIONS: It is concluded that creatine supplementation enhances total power output during the repeated bouts of supramaximal exercise separated by short resting intervals.
Assuntos
Creatina/farmacologia , Suplementos Nutricionais , Exercício Físico/fisiologia , Fadiga Muscular/efeitos dos fármacos , Músculo Esquelético/efeitos dos fármacos , Consumo de Oxigênio/efeitos dos fármacos , Esforço Físico/efeitos dos fármacos , Adolescente , Adulto , Limiar Anaeróbio/efeitos dos fármacos , Ciclismo/fisiologia , Método Duplo-Cego , Teste de Esforço , Humanos , Masculino , Fosfocreatina/biossínteseRESUMO
The Creatine kinase (CK) SYSTEM represents key in a power exchange mediators the structure capable to plural interactions with the majority energy making (Glycolysis and mitochondriuns) and energy consuming (ATPases) structures at use of one multifunctional metabolits--creatine and providing transport macroergs inside a cell. Mitochondrions CK provides synthesis creatine phosphates (CP) from cytoplasmic creatine and energy mitochondriums ATP. CP energetically also is structurally more favourable than ATphi. The MM, MB and BB isoforms provide splitting Kphi and synthesis ATphi for M-ATPases, Ca-ATPases and Na-K-ATPases accordingly. Questions of regulation of activity of enzyme, both in ontogenesis, and in blood are discussed.