Non-energy mechanism of phosphocreatine on the protection of cell survival.

If mitochondrial energy availability or oxidative metabolism is altered, patients will suffer from insufficient energy supply Phosphocreatine (PCr) not only acts as an energy carrier, but also acts as an antioxidant and defensive agent to maintain the integrity and stability of the membrane, to maintain ATP homeostasis through regulating mitochondrial respiration. Meanwhile, PCr can enhance calcium balance and reduce morphological pathological changes, ultimately, PCr helps to reduce apoptosis. On the other aspect, the activities of ATP synthase and MitCK play a crucial role in the maintenance of cellular energy metabolic function. It is interesting to note, PCr not only rises the activities of ATP synthase as well as MitCK, but also promotes these two enzymatic reactions. Additionally, PCr can also inhibit mitochondrial permeability transition in a concentration-dependent manner, prevent ROS and CytC from spilling into the cytoplasm, thereby inhibit the release of proapoptotic factors caspase-3 and caspase-9, and eventually, effectively prevent LPS-induced apoptosis of cells. Understandably, PCr prevents the apoptosis caused by abnormal mitochondrial energy metabolism and has a protective role in a non-energy manner. Moreover, recent studies have shown that PCr protects cell survival through PI3K/Akt/eNOS, MAPK pathway, and inhibition of Ang II-induced NF-κB activation. Furthermore, PCr antagonizes oxidative stress through the activation of PI3K/Akt/GSK3b intracellular pathway, PI3K/AKT-PGC1α signaling pathway, while through the promotion of SIRT3 expression to maintain normal cell metabolism. Interestingly, PCr results in delaying the time to enter pathological metabolism through the delayed activation of AMPK pathway, which is different from previous studies, now we propose the hypothesis that the "miRNA-JAK2/STAT3 -CypD pathway" may take part in protecting cells from apoptosis, PCr may be further be involved in the dynamic relationship between CypD and STAT3. Furthermore, we believe that PCr and CypD would be the central link to maintain cell survival and maintain cell stability and mitochondrial repair under the mitochondrial dysfunction caused by oxidative stress. This review provides the modern progress knowledge and views on the molecular mechanism and molecular targets of PCr in a non-energy way.

Muscle metabolic status and acid-base balance during 10-s work:5-s recovery intermittent and continuous exercise.

Gastrocnemius muscle phosphocreatine ([PCr]) and hydrogen ion ([H(+)]) were measured using (31)P-magnetic resonance spectroscopy during repeated bouts of 10-s heavy-intensity (HI) exercise and 5-s rest compared with continuous (CONT) HI exercise. Recreationally active male subjects (n = 7; 28 yr ± 9 yr) performed on separate occasions 12 min of isotonic plantar flexion (0.75 Hz) CONT and intermittent (INT; 10-s exercise, 5-s rest) exercise. The HI power output in both CONT and INT was set at 50% of the difference between the power output associated with the onset of intracellular acidosis and peak exercise determined from a prior incremental plantar flexion protocol. Intracellular concentrations of [PCr] and [H(+)] were calculated at 4 s and 9 s of the work period and at 4 s of the rest period in INT and during CONT exercise. [PCr] and [H(+)] (mean ± SE) were greater at 4 s of the rest periods vs. 9 s of exercise over the course of the INT exercise bout: [PCr] (20.7 mM ± 0.6 vs. 18.7 mM ± 0.5; P < 0.01); [H(+)] (370 nM ± 13.50 vs. 284 nM ± 13.6; P < 0.05). Average [H(+)] was similar for CONT vs. INT. We therefore suggest that there is a glycolytic contribution to ATP recovery during the very short rest period (<5 s) of INT and that the greater average power output of CONT did not manifest in greater [H(+)] and greater glycolytic contribution compared with INT exercise.

The slow components of phosphocreatine and pulmonary oxygen uptake can be dissociated during heavy exercise according to training status.

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.

Creatine phosphate: pharmacological and clinical perspectives.

Since the 1970s, extensive experimental and clinical research has demonstrated that relevant reductions of creatine phosphate (CrP) or phosphocreatine availability occur in a wide spectrum of pathophysiological situations. A decrease in intracellular concentrations of creatine (Cr) and CrP results in a hypodynamic state of cardiac and skeletal muscle pathology. Many experimental and clinical studies have evaluated the possibility to improve cardiac and skeletal muscle performance by exogenous administration of CrP. Furthermore, many experimental studies have shown that CrP may play two important roles in the regulation of muscle energetics and work. First, CrP maintains local adenosine triphosphate pools and stabilizes cellular membranes due to electrostatic interactions with phospholipids. The second mechanism decreases the production of lysophosphoglycerides in hypoxic hearts, protects the sarcolemma of cardiac cells against ischemic damage, decreases the frequency of arrhythmias, and increases post-ischemic recovery of contractile function. Recent research on CrP has demonstrated positive therapeutic results in various clinical applications. These benefits have been applied in several pathological conditions, such as heart failure, acute myocardial ischemia, chronic ischemic heart disease, cardiac surgery, skeletal muscle hypotonotrophy, and cerebral ischemia. This review describes the CrP shuttle, pathophysiological basis of the supplementation of CrP, and its therapeutic effects in multiple clinical conditions. The major aim is to summarize results of the intense research carried out over 40 years to provide evidence to support the adjunctive use of CrP in many pathological conditions that may target cellular energy impairment; thus, increasing energy metabolism.

Repeated-sprint ability - part II: recommendations for training.

Short-duration sprints, interspersed with brief recoveries, are common during most team sports. The ability to produce the best possible average sprint performance over a series of sprints (≤10 seconds), separated by short (≤60 seconds) recovery periods has been termed repeated-sprint ability (RSA). RSA is therefore an important fitness requirement of team-sport athletes, and it is important to better understand training strategies that can improve this fitness component. Surprisingly, however, there has been little research about the best training methods to improve RSA. In the absence of strong scientific evidence, two principal training theories have emerged. One is based on the concept of training specificity and maintains that the best way to train RSA is to perform repeated sprints. The second proposes that training interventions that target the main factors limiting RSA may be a more effective approach. The aim of this review (Part II) is to critically analyse training strategies to improve both RSA and the underlying factors responsible for fatigue during repeated sprints (see Part I of the preceding companion article). This review has highlighted that there is not one type of training that can be recommended to best improve RSA and all of the factors believed to be responsible for performance decrements during repeated-sprint tasks. This is not surprising, as RSA is a complex fitness component that depends on both metabolic (e.g. oxidative capacity, phosphocreatine recovery and H+ buffering) and neural factors (e.g. muscle activation and recruitment strategies) among others. While different training strategies can be used in order to improve each of these potential limiting factors, and in turn RSA, two key recommendations emerge from this review; it is important to include (i) some training to improve single-sprint performance (e.g. 'traditional' sprint training and strength/power training); and (ii) some high-intensity (80-90% maximal oxygen consumption) interval training to best improve the ability to recover between sprints. Further research is required to establish whether it is best to develop these qualities separately, or whether they can be developed concurrently (without interference effects). While research has identified a correlation between RSA and total sprint distance during soccer, future studies need to address whether training-induced changes in RSA also produce changes in match physical performance.

Repeated-sprint ability - part I: factors contributing to fatigue.

Short-duration sprints (<10 seconds), interspersed with brief recoveries (<60 seconds), are common during most team and racket sports. Therefore, the ability to recover and to reproduce performance in subsequent sprints is probably an important fitness requirement of athletes engaged in these disciplines, and has been termed repeated-sprint ability (RSA). This review (Part I) examines how fatigue manifests during repeated-sprint exercise (RSE), and discusses the potential underpinning muscular and neural mechanisms. A subsequent companion review to this article will explain a better understanding of the training interventions that could eventually improve RSA. Using laboratory and field-based protocols, performance analyses have consistently shown that fatigue during RSE typically manifests as a decline in maximal/mean sprint speed (i.e. running) or a decrease in peak power or total work (i.e. cycling) over sprint repetitions. A consistent result among these studies is that performance decrements (i.e. fatigue) during successive bouts are inversely correlated to initial sprint performance. To date, there is no doubt that the details of the task (e.g. changes in the nature of the work/recovery bouts) alter the time course/magnitude of fatigue development during RSE (i.e. task dependency) and potentially the contribution of the underlying mechanisms. At the muscle level, limitations in energy supply, which include energy available from phosphocreatine hydrolysis, anaerobic glycolysis and oxidative metabolism, and the intramuscular accumulation of metabolic by-products, such as hydrogen ions, emerge as key factors responsible for fatigue. Although not as extensively studied, the use of surface electromyography techniques has revealed that failure to fully activate the contracting musculature and/or changes in inter-muscle recruitment strategies (i.e. neural factors) are also associated with fatigue outcomes. Pending confirmatory research, other factors such as stiffness regulation, hypoglycaemia, muscle damage and hostile environments (e.g. heat, hypoxia) are also likely to compromise fatigue resistance during repeated-sprint protocols.

Lower aerobic capacity was associated with abnormal intramuscular energetics in patients with metabolic syndrome.

Lower aerobic capacity is a strong and independent predictor of cardiovascular morbidity and mortality in patients with metabolic syndrome (MetS). However, the mechanisms are not fully elucidated. We tested the hypothesis that skeletal muscle dysfunction could contribute to the lower aerobic capacity in MetS patients. The incremental exercise tests with cycle ergometer were performed in 12 male patients with MetS with no habitual exercise and 11 age-, sex- and activity-matched control subjects to assess the aerobic capacity. We performed (31)phosphorus-magnetic resonance spectroscopy (MRS) to assess the high-energy phosphate metabolism in skeletal muscle during aerobic exercise. Proton-MRS was also performed to measure intramyocellular lipid (IMCL) content. Peak oxygen uptake (peak VO(2); 34.1±6.2 vs. 41.4±8.4 ml kg(-1) min(-1), P<0.05) and anaerobic threshold (AT; 18.0±2.4 vs. 23.1±3.7 ml kg(-1) min(-1), P<0.01) adjusted by lean body mass were lower in MetS patients than control subjects. Phosphocreatine (PCr) loss during exercise was 1.5-fold greater in MetS, suggesting reduced intramuscular oxidative capacity. PCr loss was inversely correlated with peak VO(2) (r=-0.64) and AT (r=-0.60), respectively. IMCL content was threefold higher in MetS and was inversely correlated with peak VO(2) (r=-0.47) and AT (r=-0.52), respectively. Moreover, there was a positive correlation between IMCL content and PCr loss (r=0.64). These results suggested that lean-body aerobic capacity in MetS patients was lower compared with activity-matched healthy subjects, which might be due to the reduced intramuscular fatty acid oxidative metabolism.

Computer-aided analysis of biochemical mechanisms that increase metabolite and proton stability in the heart during severe hypoxia and generate post-ischemic PCr overshoot.

During severe hypoxia in the heart, impaired supply of ATP by oxidative phosphorylation could lead to a great drop in ATP turnover and heart work. Anaerobic glycolysis enables unchanged ATP turnover to be maintained, but leads to huge changes in metabolite (PCr, ATP, ADP, P (i)) concentrations and to cytosol acidification. A computer model of heart energetics developed previously is used to analyze semi-quantitatively the effect of different processes/mechanisms that can partly counteract these effects. Down-regulation of ATP usage compromises cardiac output, but reduces changes in cytosolic pH and metabolite concentrations. AMP decomposition delays cytosol acidification but reduces metabolite homeostasis (concentration stability). An increase in the parallel activation of oxidative phosphorylation (OXPHOS) (a hypothetical mechanism involving direct activation of all OXPHOS complexes by a cytosolic factor, postulated to take place also during work increase) reduces cytosol acidification and elevates metabolite homeostasis. All these mechanisms can generate the post-ischemic PCr overshoot.

Skeletal muscle phosphocreatine recovery after submaximal exercise in children and young and middle-aged adults.

CONTEXT: Elderly subjects have reduced mitochondrial function. However, it remains unclear whether the decline in mitochondrial function begins earlier in the life span. OBJECTIVE: The objective of the study was to determine skeletal muscle mitochondrial oxidative phosphorylation by (31)phosphorous-magnetic resonance spectroscopy (MRS) across a variety of age groups. DESIGN: This was a cross-sectional study of 121 healthy normal-weight and overweight individuals from age 8 to 55 yr. SETTING: The study was conducted at a single university medical center in Boston, MA. PARTICIPANTS: Participants included 68 children and 53 adults from the Boston community. INTERVENTIONS AND MAIN OUTCOME MEASURES: Phosphocreatine (PCr) recovery was evaluated by (31)phosphorous-MRS after submaximal exercise. Subjects were also evaluated with anthropometric measurements, metabolic profiles, and measures of physical activity. RESULTS: PCr recovery determined by (31)phosphorous-MRS is positively associated with age in univariate analysis in a cohort of individuals aged 8-55 yr (r = +0.55, P < 0.0001). Stratification of subjects into four age groups (prepubertal and early pubertal children, pubertal and postpubertal children < 18 yr, young adults aged 18-39 yr, and middle aged adults aged 40-55 yr) demonstrates prolongation of PCr recovery with increasing age across the four groups (P < 0.0001 by ANOVA). The relationship between PCr recovery and age remains strong when controlling for gender; race; ethnicity; body mass index; measures of physical activity and inactivity; and anthropometric, nutritional, and metabolic parameters (P < 0.004). CONCLUSIONS: Skeletal muscle PCr recovery measured by (31)phosphorous-MRS is prolonged with age, even in children and young adults.

Modular regulation analysis of heart contraction: application to in situ demonstration of a direct mitochondrial activation by calcium in beating heart.

Heart contraction is characterized by the absence of changes in energetic intermediates in response to a large increase of activity. Until now no experimental approach could address this question concerning the intact beating heart. Ca(2+) plays a crucial role in the excitation-contraction coupling, and in vitro studies have evidenced that Ca(2+) may also directly activate mitochondrial oxidative phosphorylation. We applied our new in situ modular control and regulation analysis on isolated beating rat heart perfused under two different calcium concentrations with pyruvate or glucose as the substrate. Modular control analysis demonstrated experimentally that, although control by energy production was slightly higher under glucose conditions compared with pyruvate, most of the control of heart contraction resides in energy utilization. This behavior is the direct consequence of the high sensitivity (elasticity) of the energy producer processes to ATP utilization. Interestingly, the increase in heart metabolic rate by Ca(2+) did not significantly change the pattern of control distribution. The regulation analysis performed under the two calcium conditions demonstrated a balanced activation of myofibrils ATPases, and mitochondrial ATP synthesis in response to Ca(2+) increase. This first study demonstrates in situ the hypothesis that the energetic adequation in heart contraction is mediated by a parallel activation of both processes of energy production and utilization by Ca(2+). The results presented here show that modular control and regulation analyses allow in situ study of internal regulations in intact beating heart energetics and function and may now be applied to heart dysfunctions and therapeutic effects.

In vivo 1H-magnetic resonance spectroscopy study of amygdala-hippocampal and parietal regions in autism.

OBJECTIVE: The neural basis for autistic spectrum disorders is unclear, but abnormalities in the development of limbic areas and of glutamate have been suggested. Proton magnetic resonance spectroscopy ((1)H-MRS) can be used to measure the concentration of brain metabolites. However, the concentration of glutamate/glutamine in brain regions implicated in autistic spectrum disorders has not yet been examined in vivo. METHOD: The authors used (1)H-MRS to investigate the neuronal integrity of the amygdala-hippocampal complex and a parietal control region in adults with autistic spectrum disorders and healthy subjects. RESULTS: People with autistic spectrum disorders had a significantly higher concentration of glutamate/glutamine and creatine/phosphocreatine in the amygdala-hippocampal region but not in the parietal region. CONCLUSIONS: Abnormalities in glutamate/glutamine may partially underpin the pathophysiology of autistic spectrum disorders, and the authors confirm earlier reports that limbic areas are metabolically aberrant in these disorders.

Some factors determining the PCr recovery overshoot in skeletal muscle.

It has been proposed recently that the phosphocreatine (PCr) overshoot (increase above the resting level) during muscle recovery after exercise is caused by a slow decay during this recovery of the direct activation of oxidative phosphorylation taking place during muscle work. In the present article the factors determining the appearance and size of the PCr overshoot are studied using the computer model of oxidative phosphorylation in intact skeletal muscle developed previously. It is demonstrated that the appearance and duration of this overshoot is positively correlated with the value of the characteristic decay time of the direct activation of oxidative phosphorylation. It is also shown that the size of PCr overshoot is increased by low resting PCr/Cr ratio (what is confirmed by our unpublished experimental data), by high intensity of the direct activation of oxidative phosphorylation, by high muscle work intensity and by low rate of the return of cytosolic pH to the resting value during muscle recovery.

Reduced inotropic reserve and increased susceptibility to cardiac ischemia/reperfusion injury in phosphocreatine-deficient guanidinoacetate-N-methyltransferase-knockout mice.

BACKGROUND: The role of the creatine kinase (CK)/phosphocreatine (PCr) energy buffer and transport system in heart remains unclear. Guanidinoacetate-N-methyltransferase-knockout (GAMT-/-) mice represent a new model of profoundly altered cardiac energetics, showing undetectable levels of PCr and creatine and accumulation of the precursor (phospho-)guanidinoacetate (P-GA). To characterize the role of a substantially impaired CK/PCr system in heart, we studied the cardiac phenotype of wild-type (WT) and GAMT-/- mice. METHODS AND RESULTS: GAMT-/- mice did not show cardiac hypertrophy (myocyte cross-sectional areas, hypertrophy markers atrial natriuretic factor and beta-myosin heavy chain). Systolic and diastolic function, measured invasively (left ventricular conductance catheter) and noninvasively (MRI), were similar for WT and GAMT-/- mice. However, during inotropic stimulation with dobutamine, preload-recruitable stroke work failed to reach maximal levels of performance in GAMT-/- hearts (101+/-8 mm Hg in WT versus 59+/-7 mm Hg in GAMT-/-; P<0.05). (31)P-MR spectroscopy experiments showed that during inotropic stimulation, isolated WT hearts utilized PCr, whereas isolated GAMT-/- hearts utilized P-GA. During ischemia/reperfusion, GAMT-/- hearts showed markedly impaired recovery of systolic (24% versus 53% rate pressure product recovery; P<0.05) and diastolic function (eg, left ventricular end-diastolic pressure 23+/-9 in WT and 51+/-5 mm Hg in GAMT-/- during reperfusion; P<0.05) and incomplete resynthesis of P-GA. CONCLUSIONS: GAMT-/- mice do not develop hypertrophy and show normal cardiac function at low workload, suggesting that a fully functional CK/PCr system is not essential under resting conditions. However, when acutely stressed by inotropic stimulation or ischemia/reperfusion, GAMT-/- mice exhibit a markedly abnormal phenotype, demonstrating that an intact, high-capacity CK/PCr system is required for situations of increased cardiac work or acute stress.

Metabolically assessed muscle fibre recruitment in brief isometric contractions at different intensities.

This study investigated the recruitment of type I, IIA and IIAX fibres after seven isometric contractions at 40, 70 and 100% maximal voluntary knee extension torque (MVC, 1 s on/1 s off). Biopsies of the vastus lateralis muscle were collected from seven subjects at rest and immediately post-exercise. Fibre fragments were dissected from the freeze-dried samples and characterized as type I, IIA and IIAX using mATPase staining. Phosphocreatine (PCr) and creatine (Cr) content were measured in the remaining part of characterized fibres. A decline in the ratio of PCr to Cr (PCr/Cr) was used as an indication of activation. The mean peak torques were, respectively, 39 (2), 72 (2) and 87 (6)% MVC. Cumulative distributions of type I and IIA fibres were significantly shifted to lower PCr/Cr ratios at all intensities (Kolmogorov-Smirnov test, P<0.05). The cumulative distribution of type IIAX fibres showed a significant leftward shift only at 87% MVC ( P<0.05). A hierarchical order of fibre activation with increasing intensity of exercise was found, with some indication of rate coding for type I and IIA fibres. Evidence for activation of type IIAX fibres was only found at 87% MVC.

Isolation and properties of cytoplasmic alpha-glycerol 3-phosphate dehydrogenase from the pectoral muscle of the fruit bat, Eidolon helvum.

Cytoplasmic alpha-glycerol-3-phosphate dehydrogenase from fruit-bat-breast muscle was purified by ion-exchange and affinity chromatography. The specific activity of the purified enzyme was approximately 120 units/mg of protein. The apparent molecular weight of the native enzyme, as determined by gel filtration on Sephadex G-100 was 59,500 +/- 650 daltons; its subunit size was estimated to be 35,700 +/- 140 by SDS-polyacrylamide gel electrophoresis. The true Michaelis-Menten constants for all substrates at pH 7.5 were 3.9 +/- 0.7 mM, 0.65 +/- 0.05 mM, 0.26 +/- 0.06 mM, and 0.005 +/- 0.0004 mM for L-glycerol-3-phosphate, NAD(+), DHAP, and NADH, respectively. The true Michaelis-Menten constants at pH 10.0 were 2.30 +/- 0.21 mM and 0.20 +/- 0.01 mM for L-glycerol-3-phosphate and NAD(+), respectively. The turnover number, k(cat), of the forward reaction was 1.9 +/- 0.2 x 10(4)s(-1). The treatment of the enzyme with 5,5'-dithiobis-2-nitrobenzoic acid (DTNB) under denaturing conditions indicated that there were a total of eight cysteine residues, while only two of these residues were reactive towards DTNB in the native enzyme. The overall results of the in vitro experiments suggest that alpha-glycerol-3-phosphate dehydrogenase of the fruit bat preferentially catalyses the reduction of dihydroxyacetone phosphate to glycerol-3-phosphate.

The role of phosphorylcreatine and creatine in the regulation of mitochondrial respiration in human skeletal muscle.

1. The role of phosphorylcreatine (PCr) and creatine (Cr) in the regulation of mitochondrial respiration was investigated in permeabilised fibre bundles prepared from human vastus lateralis muscle. 2. Fibre respiration was measured in the absence of ADP (V(0)) and after sequential additions of submaximal ADP (0.1 mM ADP, V(submax)), PCr (or Cr) and saturating [ADP] (V(max)). 3. V(submax) increased by 55 % after addition of saturating creatine (P < 0.01; n = 8) and half the maximal effect was obtained at 5 mM [Cr]. In contrast, V(submax) decreased by 54 % after addition of saturating phosphorylcreatine (P < 0.01; n = 8) and half the maximal effect was obtained at 1 mM [PCr]. V(max) was not affected by Cr or PCr. 4. V(submax) was similar when PCr and Cr were added simultaneously at concentrations similar to those in muscle at rest (PCr/Cr = 2) and at low-intensity exercise (PCr/Cr = 0.5). At conditions mimicking high-intensity exercise (PCr/Cr = 0.1), V(submax) increased to 60 % of V(max) (P < 0.01 vs. rest and low-intensity exercise). 5. Eight of the subjects participated in a 16 day Cr supplementation programme. Following Cr supplementation, V(0) decreased by 17 % (P < 0.01 vs. prior to Cr supplementation), whereas ADP-stimulated respiration (with and without Cr or PCr) was unchanged. 6. For the first time evidence is given that PCr is an important regulator of mitochondrial ADP-stimulated respiration. Phosphorylcreatine decreases the sensitivity of mitochondrial respiration to ADP whereas Cr has the opposite effect. During transition from rest to high-intensity exercise, decreases in the PCr/Cr ratio will effectively increase the sensitivity of mitochondrial respiration to ADP. The decrease in V(0) after Cr supplementation indicates that intrinsic changes in membrane proton conductance occur.

Effect of lactate on the synaptic potential, energy metabolism, calcium homeostasis and extracellular glutamate concentration in the dentate gyrus of the hippocampus from guinea-pig.

Towards understanding the role of glycolysis on synaptic function, we examined the effect of lactate on synaptic potential, energy metabolism, Ca(2+) homeostasis and extracellular glutamate in the dentate gyrus of guinea-pig hippocampus. Postsynaptic population spikes were recorded from the granule cell layer of the dentate gyrus in guinea-pig hippocampal slices after replacing glucose with lactate in the perfusion medium. Population spikes were not maintained and spontaneously recovered around 35min after the replacement of glucose with lactate. However, ATP levels of the dentate gyrus remained unchanged while those during the glucose-free condition decreased to 73% of the initial levels at 60min. Intracellular Ca(2+) was measured with the calcium indicator dye fura-2 AM, and the population spike was recorded simultaneously. Ca(2+) levels increased concomitantly with the early decay of synaptic potentials, and recovered partially with the spontaneous recovery of synaptic potentials. The time course of decay of population spikes and the increase of Ca(2+) levels during lactate replacement were similar to those during glucose deprivation. Increase in Ca(2+) levels during lactate replacement was completely blocked by the ryanodine receptor/calcium release channel antagonist dantrolene. Glutamate was released more significantly in the medium during lactate replacement than with normal Ringer solution, and less than that during glucose deprivation. Addition of the N-methyl-D-aspartate blocker, D-(-)-2-amino-5-phosphonovaleric acid, and the L-type calcium channel blocker, nimodipine, but not dantrolene blocked spontaneous recovery of population spikes. The results indicate that lactate can maintain energy levels in hippocampal slices, but cannot maintain ion homeostasis in granule cells of the dentate gyrus. Glycolysis plays an important role in maintaining ion homeostasis, and activation of N-methyl-D-aspartate and L-type calcium channels is necessary for support of synaptic function by lactate utilization.

Investigation of the kinetics of anaerobic metabolism by analysis of the performance of elite sprinters.

The principal motivation for the present work was the study of the kinetics of anaerobic metabolism. A new mathematical model of the bioenergetics of sprinting, incorporating a three-equation representation of anaerobic metabolism, is developed. Results computed using the model are compared with measured data from the mens' finals of the 100m event at the 1987 World Championships. The computed results closely predict the overall average performance of the competitors over the course of the entire race. Further calculations show the three-equation model of anaerobic metabolism to be a significant improvement over the previous one-equation model. Representative values of time constants that govern the rate of anaerobic energy release have been determined for elite male athletes. For phosphocreatine utilisation, values for lambda(2)=0. 20s(-1) and psi(2)=3.0s(-1) are consistent with data previously reported in the literature. New values of lambda(3)=0.033s(-1) and psi(3)=0.34s(-1) are proposed as offering an improved representation of the kinetics of oxygen-independent glycolysis. For the first time, tentative values for the time constants of ATP utilisation, lambda(1)=0.9s(-1) and psi(1)=20s(-1), are suggested. The maximum powers developed during sprinting by oxygen-independent glycolysis, PCr utilisation and endogenous ATP utilisation were calculated as 34. 1, 30.1 and 16.6Wkg(-1), respectively, with an overall maximum anaerobic power of 51.6Wkg(-1). Sample calculations show the mathematical model can be used in principle to derive data on the kinetics of anaerobic metabolism of individual athletes.