Some aspects of regulation of enzyme levels in muscle energy-supplying metabolism

Different patterns of chronic hypoxia lead to hierarchical adaptative mechanisms in goldfish metabolism

Some hypoxia-tolerant species, such as goldfish, experience intermittent and severe hypoxia in their natural habitat causing them to develop multiple physiological adaptations. However, in fish, the metabolic impact of regular hypoxic exposure on swimming performance in normoxia is less well understood. Therefore, we experimentally tested whether chronic exposure to constant (30 days at 10% air saturation) or intermittent hypoxia (3hrs in normoxia and 21hrs in hypoxia, 5 days a week) would result in similar metabolic and swimming performance benefits after reoxygenation. Moreover, half of the normoxic and intermittent hypoxic fish were put on a 20-day normoxic training regime. After these treatments, metabolic rate (standard and maximum metabolic rates: SMR and MMR) and swimming performance (critical swimming speed [Ucrit] and cost of transport [COT]) were assessed. In addition, enzyme activities (citrate synthase CS, cytochrome c oxidase COX and lactate dehydrogenase LDH) and mitochondrial respiration were examined in red muscle fibres. We found that acclimation to constant hypoxia resulted in (1) metabolic suppression (-45% SMR, and -27% MMR), (2) increased anaerobic capacity (+117% LDH), (3) improved swimming performance (+80% Ucrit, -71% COT) and (4) no changes at the mitochondrial level. Conversely, the enhancement of swimming performance was reduced following acclimation to intermittent hypoxia (+45% Ucrit, -41% COT), with a 55% decrease in aerobic scope, despite a significant increase in oxidative metabolism (+201% COX, +49% CS). This study demonstrates that constant hypoxia leads to the greatest benefit in swimming performance and that mitochondrial metabolic adjustments only provide minor help in coping with hypoxia.

Energy metabolism design of the striated muscle cell

The design of the energy metabolism system in striated muscle remains a major area of investigation. Here, we review our current understanding and emerging hypotheses regarding the metabolic support of muscle contraction. Maintenance of ATP free energy, so called energy homeostasis, via mitochondrial oxidative phosphorylation is critical to sustained contractile activity, and this major design criterion is the focus of this review. Cell volume invested in mitochondria reduces the space available for generating contractile force, and this spatial balance between mitochondria acontractile elements to meet the varying sustained power demands across muscle types is another important design criterion. This is accomplished with remarkably similar mass-specific mitochondrial protein composition across muscle types, implying that it is the organization of mitochondria within the muscle cell that is critical to supporting sustained muscle function. Beyond the production of ATP, ubiquitous distribution of ATPases throughout the muscle requires rapid distribution of potential energy across these large cells. Distribution of potential energy has long been thought to occur primarily through facilitated metabolite diffusion, but recent analysis has questioned the importance of this process under normal physiological conditions. Recent structural and functional studies have supported the hypothesis that the mitochondrial reticulum provides a rapid energy distribution system via the conduction of the mitochondrial membrane potential to maintain metabolic homeostasis during contractile activity. We extensively review this aspect of the energy metabolism design contrasting it with metabolite diffusion models and how mitochondrial structure can play a role in the delivery of energy in the striated muscle.

Muscle from grass- and grain-fed cattle differs energetically

Insufficient acidification results in dark, firm, and dry beef. While this defect is often indicative of a stress event antemortem, muscle tissue may change in response to feeding regime. Longissimus dorsi muscle samples from 10 grain-fed and 10 grass-fed market weight, angus-crossbred beef cattle were collected postmortem. Lower (P < .05) L* and a* values were recorded for steaks from grass-fed cattle. Higher (P < .05) ultimate pH values were noted in lean of grass-fed cattle compared to grain-fed cattle, yet differences in lactate, glycogen and glucose were not detected. Further, increased (P < .05) ultimate pH values and lower (P < .05) lactate accumulations were noted when samples from grass-fed cattle were subjected to an in vitro glycolysis system. Muscle from grass-fed beef possessed nearly two-fold more (P < .05) succinate dehydrogenase and (P < .001) myoglobin than that of grain-fed cattle. These data show lean from grass-fed beef has greater enzymes reflective of oxidative metabolism and suggest dark lean from grass-fed cattle may be a function of more oxidative metabolism rather than a stress-related event antemortem.

Cellular properties of extensor carpi radialis brevis and trapezius muscles in healthy males and females

In this study, we sought to determine whether differences in cellular properties associated with energy homeostasis could explain the higher incidence of work-related myalgia in trapezius (TRAP) compared with extensor carpi radialis brevis (ECRB). Tissue samples were obtained from the ECRB (n = 19) and TRAP (n = 17) of healthy males and females (age 27.9 ± 2.2 and 28.1 ± 1.5 years, respectively; mean ± SE) and analyzed for properties involved in both ATP supply and utilization. The concentration of ATP and the maximal activities of creatine phosphokinase, phosphorylase, and phosphofructokinase were higher (P < 0.05) in ECRB than TRAP. Succinic dehydrogenase, citrate synthase, and cytochrome c oxidase were not different between muscles. The ECRB also displayed a higher concentration of Na(+)-K(+)-ATPase and greater sarcoplasmic reticulum Ca(2+) release and uptake. No differences existed between muscles for either monocarboxylate transporters or glucose transporters. It is concluded that the potentials for high-energy phosphate transfer, glycogenolysis, glycolysis, and excitation-contraction coupling are higher in ECRB than TRAP. Histochemical measurements indicated that the muscle differences are, in part, related to differing amounts of type II tissue. Depending on the task demands, the TRAP may experience a greater metabolic and excitation-contraction coupling strain than the ECRB given the differences observed.

Dietary Regulation of Fat Oxidative Gene Expression in Different Skeletal Muscle Fiber Types

OBJECTIVE

To determine the effect of a high-fat diet on the expression of genes important for fat oxidation, the protein abundance of the transcription factors peroxisome proliferator-activated receptor (PPAR) isoforms alpha and gamma, and selected enzyme activities in type I and II skeletal muscle.

RESEARCH METHODS AND PROCEDURES

Sprague-Dawley rats consumed either a high-fat (HF: 78% energy, n = 8) or high-carbohydrate (64% energy, n = 8) diet for 8 weeks while remaining sedentary.

RESULTS

The expression of genes important for fat oxidation tended to increase in both type I (soleus) and type II (extensor digitorum longus) fiber types after an HF dietary intervention. However, the expression of muscle type carnitine palmitoyltransferase I was not increased in extensor digitorum longus. Analysis of the gene expression of both peroxisome proliferator-activated receptor-gamma coactivator and fork-head transcription factor O1 demonstrated no alteration in response to the HF diet. Similarly, PPARalpha and PPARgamma protein levels were also not altered by the HF diet.

DISCUSSION

An HF diet increased the expression of an array of genes involved in lipid metabolism, with only subtle differences evident in the response within differing skeletal muscle fiber types. Despite changes in gene expression, there were no effects of diet on peroxisome proliferator-activated receptor-gamma coactivator and fork-head transcription factor O1 mRNA and the protein abundance of PPARalpha and PPARgamma.

Muscle cellular properties in the ice hockey player: a model for investigating overtraining?

In this study, we hypothesized that athletes involved in 5-6 months of sprint-type training would display higher levels of proteins and processes involved in muscle energy supply and utilization. Tissue was sampled from the vastus lateralis of 13 elite ice hockey players (peak oxygen consumption = 51.8 ± 1.3 mL·kg(-1)·min(-1); mean ± standard error) at the end of a season (POST) and compared with samples from 8 controls (peak oxygen consumption = 45.5 ± 1.4 mL·kg(-1)·min(-1)) (CON). Compared with CON, higher activities were observed in POST (p < 0.05) only for succinic dehydrogenase (3.32 ± 0.16 mol·(mg protein)(-1)·min(-1) vs. 4.10 ± 0.11 mol·(mg protein)(-1)·min(-1)) and hexokinase (0.73 ± 0.05 mol·(mg protein)(-1)·min(-1) vs. 0.90 ± 0.05mol·(mg protein)(-1)·min(-1)) but not for phosphorylase, phosphofructokinase, and creatine phosphokinase. No differences were found in Na(+),K(+)-ATPase concentration (β(max): 262 ± 36 pmol·(g wet weight)(-1) vs. 275 ± 27 pmol·(g wet weight)(-1)) and the maximal activity of the sarcoplasmic reticulum Ca(2+)-ATPase (98.1 ± 6.1 µmol·(g protein)(-1)·min(-1) vs. 102 ± 3.3 µmol·(g protein)(-1)·min(-1)). Cross-sectional area was lower (p < 0.05) in POST but only for the type IIA fibres (6312 ± 684 μm(2) vs. 5512 ± 335 μm(2)), while the number of capillary counts per fibre and the capillary to fibre area ratio were generally higher (p < 0.05). These findings suggest that elite trained ice hockey players display elevations only in support of glucose-based aerobic metabolism that occur in the absence of alterations in excitation-contraction processes.

Alterations in muscular oxidative metabolism parameters in incremental treadmill exercise test in untrained rats

The present study investigates the effects of incremental exercise test on muscular oxidative metabolism. Thirty-six 2-month-old male Wistar rats were distributed in seven groups that performed exercise at different levels: first level (control), second level (0.6 km/h), third level (0.6 and 0.8 km/h), fourth level (0.6, 0.8 and 1.0 km/h), fifth level (0.6, 0.8, 1.0 and 1.2 km/h), sixth level (0.6, 0.8, 1.0, 1.2 and 1.4 km/h), and seventh level (0.6, 0.8, 1.0, 1.2, 1.4 and 1.6 km/h). At the end of the exercise challenge, level of blood lactate (BL), glycogen content (MG), creatine kinase (CK), complexes (CI, CII, CIII, CIV), oxidative damage, succinate dehydrogenase (SDH), cytochrome c oxidase as well as antioxidant enzymes (SOD and CAT) expression were measured. The speed of 1.0 km/h increased BL level, while 1.2 km/h decreased MG and increased serum CK. Increased SDH expression was observed after intensity levels 6 and 7, and cytochrome c oxidase expression increased after levels 5, 6 and 7, in comparison with lower intensity levels, ETC enzyme activities increased when exercise was applied at intensities of 0.8 km/h (CI), 1.0 km/h (CII and CIII), and 1.2 km/h (CIV). The increase in SOD expression did not occur as observed for superoxide production, except for rats that underwent exercise at level 7, but CAT expression increased significantly in all levels, starting from level 3. Our results show interesting alterations in the muscular metabolism parameters, and suggest a differential response of muscle oxidative metabolism when intense exercise is applied at different speeds.

Cellular responses in skeletal muscle to a season of ice hockey

We hypothesized that a season of ice hockey would result in extensive remodeling of muscle. Tissue sampled from the vastus lateralis of 15 players (age = 20.6 ± 0.4 years; mean ± SE) prior to (PRE) and following (POST) a season was used to characterize specific adaptations. Measurement of representative metabolic pathway enzymes indicated higher maximal activities in POST than in PRE (p < 0.05) for succinic dehydrogenase (3.26 ± 0.31 vs. 3.91 ± 0.11 mol mg protein(-1) min(-1)), citrate synthase (7.26 ± 0.70 vs. 8.70 ± 0.55 mol mg protein(-1) min(-1)), and phosphofructokinase (12.8 ± 1.3 vs. 14.4 ± 0.96 mol mg protein(-1) min(-1)) only. The season resulted in an increase in Na+-K+-ATPase concentration (253 ± 6.3 vs. 265 ± 6.0 pmol g(-1) wet weight), a decrease (p < 0.05) in maximal activity of the sarcoplasmic reticulum Ca2+-ATPase (107 ± 4.2 micromol g protein(-1) min(-1) vs. 92.0 ± 4.6 micromol g protein(-1) min(-1)), and no change in the distribution (%) of fibre types. A smaller (p < 0.05) cross-sectional area (CSA) for both type I (-11.7%) and type IIA (-18.2%) fibres and a higher (p < 0.05) capillary count/CSA for type I (+17.9%) and type IIA (+17.2%) were also found over the season. No changes were found in peak oxygen consumption (51.4 ± 1.2 mL kg(-1) min(-1) vs. 52.3 ± 1.3 mL kg(-1) min(-1)). The results suggest, based on the alterations in oxidative and perfusion potentials and muscle mass, that the dominant adaptations are in support of oxidative metabolism, which occurs at the expense of fibre CSA and possibly force-generating potential.

Cellular assessment of muscle in COPD: case studies of two males

The objective of this paper is to provide an overview of the recent developments in muscle physiology and biochemistry in general, and with respect to chronic obstructive pulmonary disease (COPD) specifically. As a way of illustration, we have presented data on the remodeling that occurs in vastus lateralis in two patients with COPD (COPD #1, forced expiratory volume in one second/forced vital capacity [FEV₁/FVC] = 63%; COPD #2, FEV₁/FVC = 41%) exhibiting differences in muscle wasting as compared to healthy controls (CON; FEV₁/FVC = 111 ± 2.2%, n = 4). Type I fibers percentages were lower in both COPD #1 (16.7) and COPD #2 (24.9) compared to CON (57.3 ± 5.2). Cross sectional area of the type I fibers of the patients ranged between 65%–68% of CON and for the type II subtypes (IIA, IIAX, IIX) between 74% and 89% (COPD #1) and 17%–32% (COPD #2). A lower number of capillary contacts were observed for all fiber types in COPD #1 but not COPD #2. Lower concentrations of adenosine triphosphate (ATP) (24%–26%) and phosphocreatine (18%–20%), but not lactate occurred in COPD. In contrast to COPD #1, who displayed normal glucose transporter content, GLUT1 and GLUT4 were only 71% and 54%, respectively of CON in COPD #2. Lower monocarboxylate contents were found for MCT1 in both COPD #1 (63%) and COPD #2 (41%) and for MCT4 (78%) in COPD #1. Maximal oxidative enzyme activities (V_max) for COPD #2 ranged between 37% (succinic dehydrogenase) and 70% (cytochrome C oxidase) of CON. For the cytosolic enzymes, V_max ranged between 89% (hexokinase) to 31% (pyruvate kinase) of CON. Depressions were also observed in V_max of the Na⁺-K⁺-ATPase for COPD #1 (66% of CON) but not COPD #2 (92% of CON) while V_max of the Ca²⁺-ATPase was near normal in COPD #1 (84% CON). It is concluded that disturbances can occur in muscle to a wide range of excitation, contraction and metabolic processes in COPD.

Scientific advances in the genetic understanding and diagnosis of malignant hyperthermia

Malignant hyperthermia (MH), a potentially fatal disorder triggered by certain types of general anesthesia, has received much attention in the scientific literature. From the first case report in 1960 until the present, hundreds of studies have been conducted. The diagnosis of MH has evolved from subjective assumptions by family history and clinical diagnosis to more sophisticated laboratory testing. A genetic basis for MH was recognized in the early 1990s and, since then, complex genetic pathways have been demonstrated. The purpose of this paper is to summarize the research literature on what is known scientifically about the diagnosis and genetic basis of MH.

Organization of metabolic pathways in vastus lateralis of patients with chronic obstructive pulmonary disease

The objective of this study was to determine whether patients with chronic obstructive lung disease (COPD) display differences in organization of the metabolic pathways and segments involved in energy supply compared with healthy control subjects. Metabolic pathway potential, based on the measurement of the maximal activity (Vmax) of representative enzymes, was assessed in tissue extracted from the vastus lateralis in seven patients with COPD (age 67 ± 4 yr; FEV1/FVC = 44 ± 3%, where FEV1is forced expiratory volume in 1 s and FVC is forced vital capacity; means ± SE) and nine healthy age-matched controls (age 68 ± 2 yr; FEV1/FVC = 75 ± 2%). Compared with control, the COPD patients displayed lower ( P < 0.05) Vmax(mol·kg protein−1·h−1) for cytochrome c oxidase (COX; 21.2 ± 2.0 vs. 28.7 ± 2.2) and 3-hydroxyacyl-CoA dehydrogenase (HADH; 2.54 ± 0.14 vs. 3.74 ± 0.12) but not citrate synthase (CS; 2.20 ± 0.16 vs. 3.19 ± 0.5). While no differences between groups were observed in Vmaxfor creatine phosphokinase, phosphorylase (PHOSPH), phosphofructokinase (PFK), pyruvate kinase, and lactate dehydrogenase, hexokinase (HEX) was elevated in COPD ( P < 0.05). Enzyme activity ratios were higher ( P < 0.05) for HEX/CS, HEX/COX, PHOSPH/HADH and PFK/HADH in COPD compared with control. It is concluded that COPD patients exhibit a reduced potential for both the electron transport system and fat oxidation and an increased potential for glucose phosphorylation while the potential for glycogenolysis and glycolysis remains normal. A comparison of enzyme ratios indicated greater potentials for glucose phosphorylation relative to the citric acid cycle and the electron transport chain and glycogenolysis and glycolysis relative to β-oxidation.

The constant proportion enzyme group concept in the selection of reference enzymes in metabolism

Comparative analyses of enzyme activity patterns reveal groups of enzymes with constant proportions and enzymes with variable proportions of their maximum activities. Constant proportion groups comprise enzymes of unbranched metabolic sequences or functionally related pathways. Ratios of constant proportion groups reflect metabolic correlations, which may be used as discriminative magnitudes of metabolic specialization. Comparison of closely related muscles reveals that differences in the absolute levels of the constant proportion group enzymes of glycolysis parallel differences in maximum glycolytic flux rates. This holds for near-equilibrium as well as for non-equilibrium enzymes. In any case, maximum enzyme activities are significantly higher than maximum metabolic flux rates. Maximum enzyme activities therefore do not permit conclusions on maximum metabolic capacities to be drawn. They may, however, be compared in closely related tissues or different metabolic conditions of a given tissue as relative magnitudes of maximum flux rates. Reference enzymes of constant proportion groups as well as of other enzymes which are representative of distinct metabolic pathways may be used in this sense for the evaluation of enzyme activity patterns. Selection of appropriate enzymes depends on the aim of the intended study, on a thorough knowledge of their individual properties, and on the possibility of measuring their maximum activity under reproducible conditions.

Acute responses in muscle mitochondrial and cytosolic enzyme activities during heavy intermittent exercise

To examine the effects of repetitive bouts of heavy exercise on the maximal activities of enzymes representative of the major metabolic pathways and segments, 13 untrained volunteers [peak aerobic power (V̇o2 peak) = 44.3 ± 2.3 ml·kg−1·min−1] cycled at ∼91% V̇o2 peak for 6 min once per hour for 16 h. Maximal enzyme activities ( Vmax, mol·kg−1·protein·h−1) were measured in homogenates from tissue extracted from the vastus lateralis before and after exercise at repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). For the mitochondrial enzymes, exercise resulted in reductions ( P < 0.05) in cytochrome- c oxidase (COX, 14.6%), near significant reductions in malate dehydrogenase (4.06%; P = 0.06) and succinic dehydrogenase (4.82%; P = 0.09), near significant increases in β-hydroxyacyl-CoA dehydrogenase (4.94%; P = 0.08), and no change in citrate synthase (CS, 2.88%; P = 0.37). For the cytosolic enzymes, exercise reduced ( P < 0.05) Vmax in hexokinase (Hex, 4.4%), creatine phosphokinase (9.0%), total phosphorylase (13.5%), phosphofructokinase (16.6%), pyruvate kinase (PK, 14.1%) and lactate dehydrogenase (10.7%). Repetition-dependent reductions ( P < 0.05) in Vmax were observed for CS (R1, R2 > R16), COX (R1, R2 > R16), Hex (1R, 2R > R16), and PK (R9 > R16). It is concluded that heavy exercise results in transient reductions in a wide range of enzymes involved in different metabolic functions and that in the case of selected enzymes, multiple repetitions of the exercise reduce average Vmax.

Rapid upregulation of GLUT-4 and MCT-4 expression during 16 h of heavy intermittent cycle exercise

In this study, we have investigated the hypothesis that an exercise protocol designed to repeatedly induce a large dependence on carbohydrate and large increases in glycolytic flux rate would result in rapid increases in the principal glucose and lactate transporters in working muscle, glucose transporter (GLUT)-4 and monocarboxylate transporter (MCT)4, respectively, and in activity of hexokinase (Hex), the enzyme used to phosphorylate glucose. Transporter abundance and Hex activity were assessed in homogenates by Western blotting and quantitative chemiluminescence and fluorometric techniques, respectively, in samples of tissue obtained from the vastus lateralis in 12 untrained volunteers [peak aerobic power (V̇o2peak) = 44.3 ± 2.3 ml·kg−1·min−1] before cycle exercise at repetitions 1 (R1), 2 (R2), 9 (R9), and 16 (R16). The 16 repetitions of the exercise were performed for 6 min at ∼90% V̇o2peak, once per hour. Compared with R1, GLUT-4 increased ( P < 0.05) by 28% at R2 and remained elevated ( P < 0.05) at R9 and R16. For MCT-4, increases ( P < 0.05) of 24% were first observed at R9 and persisted at R16. No changes were observed in GLUT-1 and MCT-1 or in Hex activity. The ∼17- to 24-fold increase ( P < 0.05) in muscle lactate observed at R1 and R2 was reduced ( P < 0.05) to an 11-fold increase at R9 and R16. It is concluded that an exercise protocol designed to strain muscle carbohydrate reserves and to result in large increases in lactic acid results in a rapid upregulation of both GLUT-4 and MCT-4.

Effects of ryanodine on skeletal muscle lactate and pyruvate in malignant hyperthermia-susceptible and normal swine as assessed by microdialysis

BACKGROUND

The caffeine/halothane contracture test in North America and the in vitro contracture test in Europe are currently the only validated bioassays for diagnosing malignant hyperthermia susceptibility and phenotyping families. Both tests are invasive requiring surgical muscle biopsy. Here, we report first use of the selective ryanodine receptor type I agonist ryanodine in a percutaneous microdialysis protocol designed to test whether microdialysis-induced local metabolic responses of skeletal muscle due to ryanodine receptor activation can differentiate between malignant hyperthermia-sensitive and normal pigs.

METHODS

Six microdialysis catheters were implanted percutaneously into the adductor muscles of the right and left thighs of malignant hyperthermia-susceptible (n = 9) and normal (n = 8) anaesthetized (ketamine/propofol) and mechanically ventilated swine. Systemic blood gases, haemodynamic parameters and creatine kinase levels were measured before, during and after microdialysis perfusion of ryanodine. After a post-implantation equilibration period of 30 min, one catheter perfused (2 micro min-1) with 0.9% NaCl (control) and was compared with the remaining five catheters perfused with increasing concentrations of ryanodine (0.2-100 micromol). Lactate and pyruvate levels were measured enzymatically.

RESULTS

Continuous perfusion with ryanodine revealed dose-dependent sigmoidal increases in the dialysate lactate and lactate-pyruvate ratio parameters; these effects were greatly augmented in malignant hyperthermia-susceptible pigs compared to normal pigs (two- to threefold): estimated EC50 greatly decreased (>19-fold) while the maximum effect increased (>twofold) in the malignant hyperthermia-susceptible group.

CONCLUSION

The in vivo percutaneous microdialysis protocol for skeletal muscle, using ryanodine as the ryanodine receptor type I agonist and dialysed lactate-pyruvate parameters as metabolic index, can reproducibly differentiate between malignant hyperthermia-susceptible and normal swine.

Adaptations to diving hypoxia in the heart, kidneys and splanchnic organs of harbor seals (Phoca vitulina)

Pinnipeds (seals and sea lions) have an elevated mitochondrial volume density [VV(mt)] and elevated citrate synthase (CS) and beta-hydroxyacyl-CoA dehydrogenase (HOAD) activities in their swimming muscles to maintain an aerobic, fat-based metabolism during diving. The goal of this study was to determine whether the heart, kidneys and splanchnic organs have an elevated VV(mt) and CS and HOAD activities as parallel adaptations for sustaining aerobic metabolism and normal function during hypoxia in harbor seals (Phoca vitulina). Samples of heart, liver, kidney, stomach and small intestine were taken from 10 freshly killed harbor seals and fixed in glutaraldehyde for transmission electron microscopy or frozen in liquid nitrogen for enzymatic analysis. Samples from dogs and rats were used for comparison. Within the harbor seal, the liver and stomach had the highest VV(mt). The liver also had the highest CS activity. The kidneys and heart had the highest HOAD activities, and the liver and heart had the highest lactate dehydrogenase (LDH) activities. Mitochondrial volume densities scaled to tissue-specific resting metabolic rate [VV(mt)/RMR] in the heart, liver, kidneys, stomach and small intestine of harbor seals were elevated (range 1.2-6.6x) when compared with those in the dog and/or rat. In addition, HOAD activity scaled to tissue-specific RMR in the heart and liver of harbor seals was elevated compared with that in the dog and rat (3.2x and 6.2x in the heart and 8.5x and 5.5x in the liver, respectively). These data suggest that organs such as the liver, kidneys and stomach possess a heightened ability for aerobic, fat-based metabolism during hypoxia associated with routine diving. However, a heightened LDH activity in the heart and liver indicates an adaptation for the anaerobic production of ATP on dives that exceed the animal's aerobic dive limit. Hence, the heart, liver, kidneys and gastrointestinal organs of harbor seals exhibit adaptations that promote an aerobic, fat-based metabolism under hypoxic conditions but can provide ATP anaerobically if required.

Metabolic enzyme activities across an altitudinal gradient: an examination of pikas (genus Ochotona)

Changes in metabolic enzyme activities were examined in three species of pikas that occur over a range of altitudes. Because these closely related mammals live in comparable ecosystems and face similar environmental factors regardless of altitude, modifications of metabolic machinery are probably due to differences in oxygen availability. Citrate synthase (CS), beta-hydroxyacyl CoA dehydrogenase (HOAD) and lactate dehydrogenase (LDH) activities were measured in heart, diaphragm, vastus lateralis, gastrocnemius and soleus muscles. Additionally, the activity levels of both M-LDH (skeletal muscle type) and H-LDH (heart type) isozymes were quantified in tissue samples. Pikas from high altitude had greater CS and HOAD activities in heart and diaphragm when compared with pikas from low altitude, while activity levels did not differ in skeletal muscles. The increase in oxidative enzyme activities in tissues with high metabolic demand is thought to enhance oxygen utilization when oxygen availability is low and may reflect greater metabolic demand on heart and diaphragm tissue. Pikas from high altitude were also found to have greater total LDH activities in all tissues examined. High altitude animals had dramatically higher H-LDH activity (2.3-3.8 times greater) while M-LDH activity was more comparable (1.8 times lower to 1.7 times greater) when compared with low altitude animals. High total LDH activity enables pikas to perform short bouts of anaerobic activity, while high levels of H-LDH isozymes may serve to enhance lactate removal and decrease recovery time in animals living at high altitude.

Large functional range of steady-state levels of nuclear and mitochondrial transcripts coding for the subunits of the human mitochondrial OXPHOS system

We have measured, by reverse transcription and real-time quantitative PCR, the steady-state levels of the mitochondrial and nuclear transcripts encoding several subunits of the human oxidative phosphorylation (OXPHOS) system, in different normal tissues (muscle, liver, trachea, and kidney) and in cultured cells (normal fibroblasts, 143B osteosarcoma cells, 143B206 rho(0) cells). Five mitochondrial transcripts and nine nuclear transcripts were assessed. The measured amounts of these OXPHOS transcripts in muscle samples corroborated data obtained by others using the serial analysis of gene expression (SAGE) method to appraise gene expression in the same type of tissue. Steady-state levels for all the transcripts were found to range over more than two orders of magnitude. Most of the time, the mitochondrial H-strand transcripts were present at higher levels than the nuclear transcripts. The mitochondrial L-strand transcript ND6 was usually present at a low level. Cultured 143B cells contained significantly reduced amounts of mitochondrial transcripts in comparison with the tissue samples. In 143B206 rho(0) cells, fully depleted of mitochondrial DNA, the levels of nuclear OXPHOS transcripts were not modified in comparison with the parental cells. This observation indicated that nuclear transcription is not coordinated with mitochondrial transcription. We also observed that in the different tissues and cells, there is a transcriptional coregulation of all the investigated nuclear genes. Nuclear OXPHOS gene expression seems to be finely regulated.

Neuromuscular fatigue during repeated exhaustive submaximal static contractions of knee extensor muscles in endurance-trained, power-trained and untrained men

The neural and muscular changes during fatigue produced in repeated submaximal static contractions of knee extensors were measured. Three groups of differently adapted male subjects (power-trained, endurance-trained and untrained, 15 in each) performed the exercise that consisted of 10 trials of submaximal static contractions at the level of 40% of maximal voluntary contraction (MVC) force till exhaustion with the inter-trial rest intervals of 1 min. MVC force, reaction time and patellar reflex time components before and after the fatiguing exercise and following 5, 10 and 15 min of recovery were recorded. Endurance-trained athletes had a significantly longer holding times for all the 10 trials compared with power-trained athletes and untrained subjects. However, no significant differences in static endurance between power-trained athletes and untrained subjects were noted. The fatigue test significantly prolonged the time between onset of electrical and mechanical activity (electromechanical delay) in voluntary and reflex contractions. The electromechanical delay in voluntary contraction condition for power-trained and untrained subjects and in reflex condition for endurance-trained subjects had not recovered 15 min after cessation of exercise. No significant changes in the central component of visual reaction time (premotor time of MVC) and latency of patellar reflex were noted after fatiguing static exercise. It is concluded, that in this type of exercise the fatigue development may be largely owing to muscle contractile failure.

Initial aerobic power does not alter muscle metabolic adaptations to short-term training

To investigate the hypothesis that training-induced increases in muscle mitochondrial potential are not obligatory to metabolic adaptations observed during submaximal exercise, regardless of peak aerobic power (VO(2 peak)) of the subjects, a short-term training study was utilized. Two groups of untrained male subjects (n = 7/group), one with a high (HI) and the other with a low (LO) VO(2 peak) (means +/- SE; 51.4 +/- 0.90 vs. 41.0 +/- 1.3 ml. kg(-1). min(-1);P < 0.05), cycled for 2 h/day at 66-69% of VO(2 peak) for 6 days. Muscle tissue was extracted from vastus lateralis at 0, 3, and 30 min of standardized cycle exercise before training (0 days) and after 3 and 6 days of training and analyzed for metabolic and enzymatic changes. During exercise after 3 days of training in the combined HI + LO group, higher (P < 0.05) concentrations (mmol/kg dry wt) of phosphocreatine (40.5 +/- 3.4 vs. 52.2 +/- 4.2) and lower (P < 0.05) concentrations of P(i) (61.5 +/- 4.4 vs. 53.3 +/- 4.4), inosine monophosphate (0.520 +/- 0.19 vs. 0.151 +/- 0.05), and lactate (37.9 +/- 5.5 vs. 22.8 +/- 4.8) were observed. These changes were also accompanied by reduced levels of calculated free ADP, AMP, and P(i). All adaptations were fully expressed by 3 min of exercise and by 3 days of training and were independent of initial VO(2 peak) levels. Moreover, maximal activity of citrate synthase, a measure of mitochondrial capacity, was only increased with 6 days of training (5.71 +/- 0.29 vs. 7.18 +/- 0.37 mol. kg protein(-1). h(-1); P < 0. 05). These results demonstrate that metabolic adaptations to prolonged exercise occur within the first 3 days of training and during the non-steady-state period. Moreover, neither time course nor magnitude of metabolic adaptations appears to depend on increases in mitochondrial potential or on initial aerobic power.

Serial effects of high-resistance and prolonged endurance training on Na+-K+ pump concentration and enzymatic activities in human vastus lateralis

The purpose of this study was to compare two contrasting training models, namely high-resistance training and prolonged submaximal training on the expression of Na+-K+ ATPase and changes in the potential of pathways involved in energy production in human vastus lateralis. The high-resistance training group (VO2peak = 45.3 +/- 1.9 mL kg(-1) min(-1), mean +/- SE, n = 9) performed three sets of six to eight repetitions maximal, each of squats, leg presses and leg extensions, three times per week for 12 weeks, while the prolonged submaximal training group (VO2peak = 44.4 +/- 6.6 mL kg(-1) min(-1), n = 7) cycled 5-6 times per week for 2 h day(-1) at 68% VO2peak for 11 weeks. In the HRT group, Na+-K+ ATPase (pmol g(-1) wet wt), measured with the 3H-ouabain binding technique, showed no change from 0 (289 +/- 22) to 4 weeks (283 +/- 15), increased (P < 0.05) by 16% at 7 weeks and remained stable until 12 weeks (319 +/- 19). For prolonged submaximal training, a 22% increase (P < 0.05) was observed from 0 (278 +/- 31) until 3 weeks (339 +/- 29) with no further changes observed at either 9 weeks (345 +/- 25) or 11 weeks (359 +/- 34). In contrast to high-resistance training, where a 15% increase (P < 0.05) was observed, only in the maximal activity of phosphorylase, prolonged submaximal training resulted in increases in malate dehydrogenase, beta-hydroxyl-CoA dehydrogenase, hexokinase and phosphofructokinase. In contrast to high-resistance training which failed to result in an increase in VO2peak, prolonged submaximal training increased VO2peak by approximately 15%. Only for prolonged exercise training was a relationship observed for VO2peak and Na+-K+-ATPase (r = 0.59; P < 0.05). Correlations between VO2peak and mitochondrial enzyme activities were not significant (P > 0.05) for either training programme. It is concluded that although both training programmes stimulate an up-regulation in Na+-K+ ATPase concentration, only the prolonged submaximal training programme enhances the potential for beta-oxidation, oxidative phosphorylation and glucose phosphorylation.

Use of cytosolic metabolite patterns to estimate free magnesium in normoxic myocardium

Cytosolic free magnesium (Mgf) is considered relatively constant. To test this concept, Mgf was estimated during hyperkalemic ventricular akinesis, normal and maximum adrenergic stimulation, and sulfate loading of the normoxic perfused guinea-pig heart. The Mgf estimates utilized a new sliding scale derived from the Mg(2+)-dependence of glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase (GAPDH/PGK). The pseudo constant K'GAPDH.K'PGK was measured as ([creatine phosphate][3-phosphoglycerate][lactate]KLDH)/([creatine][Pi] [glyceraldehyde 3-phosphate][pyruvate]KCK), which varied with magnesium due to KCK (CK, LDH = creatine kinase, lactate dehydrogenase). However, the correct magnesium dependencies of the true constants KGAPDH.KPGK and KCK were taken from the literature. The [Mg2+] at which pseudo K'GAPDH.K'PGK equalled true KGAPDH.KPGK was the best estimate of Mgf.Mgf fell to approximately 0.13 mM in hyperkalemic arrest from a control of approximately 0.6 mM, rising to approximately 0.85 mM only during maximum adrenergic stress. Mgf increased further to approximately 1.3 mM during sulfate loading which induced ATP catabolism. Mgf and ATP were reciprocally related. Thus; (1) myocardial free [Mg2+] judged from GADPH/PGK mass-action relations changed appreciably only under extreme physiological states; (2) ATP was a major chelator of Mg2+ in perfused myocardium, i.e., acute ATP pool size reduction may be associated with increments in Mgf.

Mitochondrial actaptations to chronic muscle use: Effect of iron deficiency

1. The effects of chronic muscle use on mitochondrial structure, enzymes and gene expression is reviewed. The role of iron deficiency in modulating this adaptation is discussed. 2. Chronic muscle use and disuse alter mitochondrial composition and affect mitochondrial subpopulations differentially. This has implications for an understanding of organelle assembly. 3. Iron deficiency decreases mitochondrial functional mass within muscle by reducing the level of heme and non-heme iron-containing components. This alters the metabolic response during exercise and results in a reduced endurance performance. 4. Both iron deficiency and chronic muscle use represent contrasting experimental models for the study of mitochondrial function and biogenesis.

Combined glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase in catecholamine-stimulated guinea-pig cardiac muscle. Comparison with mass-action ratio of creatine kinase

The steady-state reactant levels of triose-phosphate isomerase and the glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase system were examined in guinea-pig cardiac muscle. Key glycolytic intermediates, including glyceraldehyde 3-phosphate were directly measured and compared with those of creatine kinase. Non-working Langendorff hearts as well as isolated working hearts were perfused with 5 mM glucose (plus insulin) under normoxia conditions to maintain lactate dehydrogenase near-equilibrium. The cytosolic phosphorylation potential ([ATP]/([ADP].[Pi])) was derived from creatine kinase and the free [NAD+]/([NADH].[H+]) ratio from lactate dehydrogenase. In Langendorff hearts glycolysis was varied from near-zero flux (hyperkalemic cardiac arrest) to higher than normal flux (normal and maximum catecholamine stimulation). The triose-phosphate isomerase was near-equilibrium only in control or potassium-arrested Langendorff hearts as well as in postischemic 'stunned' hearts. However, when glycolytic flux increased due to norepinephrine or due to physiological pressure-volume work the enzyme was displaced from equilibrium. The alternative phosphorylation ratio [ATP]'/([ADP]).[Pi]) was derived from the magnesium-dependent glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase system assigning free magnesium different values in the physiological range (0.1-2.0 mM). As predicted, [ATP]/([ADP].[Pi]) and [ATP]'/([ADP]'.[Pi]') were in excellent agreement when glycolysis was virtually halted by hyperkalemic arrest (flux approximately 0.2 mumol C3.min-1.g dry mass-1). However, the equality between the two phosphorylation ratios was not abolished upon resumption of spontaneous beating and also not during adrenergic stimulation (flux approximately 5-14 mumol C3.min-1.g dry mass-1). In contrast, when flux increased due to transition from no-work to physiological pressure-volume work (rate increase from approximately 3 to 11 mumol C3.min-1.g dry mass-1), the two ratios were markedly different indicating disequilibrium of the glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase. Only during adrenergic stimulation or postischemic myocardial 'stunning', not due to hydraulic work load per se, glyceraldehyde-3-phosphate levels increased from about 4 microM to greater than or equal to 16 microM. Thus the guinea-pig cardiac glyceraldehyde-3-phosphate dehydrogenase/phosphoglycerate kinase system can realize the potential for near-equilibrium catalysis at significant flux provided glyceraldehyde-3-phosphate levels rise, e.g., due to 'stunning' or adrenergic hormones.

Turnover of sarcoplasmic proteins in the breast muscle of rapidly growing chicks

1. Turnover of the sarcoplasmic proteins aldolase, phosphoglycerate mutase, lactate dehydrogenase and creatine phosphokinase isolated from chicken breast muscle was investigated using a pulse labelling technique. 2. A single injection of [U-14C]leucine was given and the proteins were extracted and purified at 2, 6, 15, 30, 48 and 72 hr following administration. Specific radioactivity in all of these isolated enzymes showed unexpected multiple peak profiles which did not intersect with the specific radioactivity profile of the blood plasma. 3. These results were interpreted as showing that either a large proportion of these proteins was not turned over in rapidly growing muscle or that the plasma amino acid pool was not the precursor pool for muscle protein synthesis. 4. The results also suggested that at least two sub-populations of the proteins exist within the muscle tissue. 5. A further conclusion drawn from these data was that established techniques of pulse labelling may seriously overestimate the rate of protein synthesis in growing muscle.

Distribution and developmental transition of phosphoglycerate mutase and creatine phosphokinase isozymes in rat muscles of different fiber-type composition

Phosphoglycerate mutase and creatine phosphokinase have in mammals three isozymes (types MM, MB and BB) with similar tissue distribution and developmental transition in muscle cells. To assess whether the phenotype and the developmental switch of these isozymes differ in the diverse types of muscle fibers, the enzymatic activities and the isozyme patterns, analyzed by cellulose acetate electrophoresis, have been determined in rat soleus, extensor digitorum longus and gastrocnemius muscles during postnatal development. Both phosphoglycerate mutase and creatine phosphokinase activity increased in the three muscles, the increase in extensor digitorum longus and gastrocnemius being higher than in soleus. For the two enzymes the increase in activity was due to the progressive increment of the muscle-specific forms. It is concluded that whereas phosphoglycerate mutase and creatine phosphokinase type-B subunits are present at similar levels in both type I and type II muscle fibers, phosphoglycerate mutase and creatine phosphokinase type-M subunits exhibit much higher levels in type II fibers.

Pyruvate-enhanced phosphorylation potential and inotropism in normoxic and postischemic isolated working heart. Near-complete prevention of reperfusion contractile failure

Bioenergetic and hemodynamic consequences of cellular redox manipulations by 0.2-20 mM pyruvate were compared with those due to adrenergic stress (0.7-1.1 microM norepinephrine) using isolated working guinea-pig hearts under the conditions of normoxia, low-flow ischemia, and reperfusion. 5 mM glucose (+ 5 U/l insulin) + 5 mM lactate were the basal energy-yielding substrates. To stabilize left ventricular enddiastolic pressure, ventricular filling pressure was held at 12 cmH2O under all conditions; this preload control minimized Frank-Starling effects on ventricular inotropism. Global low-flow ischemia was induced by reducing aortic pressure to levels (20-10 cmH2O) below the coronary autoregulatory reserve. Reactants of the creatine kinase, including H+ and other key metabolites, were measured by enzymatic, HPLC, and polarographic techniques. In normoxic hearts, norepinephrine stimulations of inotropism, heart rate x pressure product, and oxygen consumption (MVO2) were associated with a fall in the cytosolic phosphorylation potential [( ATP]/[( ADP].[Pi]] as judged by the creatine kinase equilibrium. In contrast, infusion of excess pyruvate (5 mM) markedly increased [ATP]/[( ADP].[Pi]) and ventricular work output, while intracellular phosphate decreased; MVO2 remained constant under the same conditions. During reperfusion following ischemia, pyruvate effected striking and concentration-dependent increases in MVO2, phosphorylation potential, and inotropism. Pyruvate dehydrogenase flux was augmented during reperfusion hyperemia followed by near-complete recoveries of [ATP]/([ADP].[Pi]), contractile force, heart rate x pressure product, and MVO2 in the presence of 5-10 mM pyruvate. Pyruvate also attenuated ischemic adenylate degradation. Omission of glucose from the perfusion medium rendered pyruvate ineffective in postischemic hearts. Similarly, excess lactate (5-15 mM) or acetate (5 mM) failed to reenergize reperfused hearts and severe depressions of MVO2 and inotropism developed despite the presence of glucose. Apparently, subcellular redox manipulations by pyruvate dissociated stimulated mitochondrial respiration and increased inotropism from low cytosolic phosphorylation potentials. This was evidence against the extramitochondrial [ADP].[Pi]/[ATP] ratio being the primary factor in the control of mitochondrial respiration. The mechanism of pyruvate enhancement of inotropism during normoxia and reperfusion is probably multifactorial. Thermodynamic effects on subcellular [NADH]/[NAD+] ratios are coupled with a rise in the cytosolic [ATP]/[( ADP].[Pi]) ratio at constant (normoxia) or increased (reperfusion) MVO2.(ABSTRACT TRUNCATED AT 400 WORDS)

Differential response of enzyme activities in rat diaphragm and intercostal muscles to exercise training

To determine whether respiratory muscles undergo alterations in enzyme activities of energy metabolism as a result of increased mechanical activity, adult male Wistar rats were subjected to a prolonged endurance training program. Analysis off maximal enzyme activity patterns in the diaphragm following 15 weeks of extreme training (final running duration: 210 min per day, 27 m.min-1 at 15 degrees grade, indicated significant reductions in the marker enzymes of the citric acid cycle (citrate synthase), glycolysis (pyruvate kinase, PK; lactate dehydrogenase, LDH), ketone body utilization (3-keto acid: CoA transferase) and transamination (glutamate pyruvate transaminase, GPT). No changes were found for the enzymes of glycogenolysis (phosphorylase, PHOSPH), glycolysis (glyceraldehyde phosphate dehydrogenase, GAPDH), glucose phosphorylation (hexokinase, HK) and beta-oxidation (3-hydroxyacyl: CoA dehydrogenase, HAD) following training. In contrast, in the external intercostal muscle, increases in the range of 57-77% were noted for the enzymes CS and HAD, whereas in the internal intercostal muscles no training induced alteration was evident for these enzymes. For both the intercostal muscles, a consistent trend was noted towards a reduction in all of the glycolytic enzymes investigated, however, significantly lower values were recorded for only PK and LDH in the internal intercostals. GPT was increased in the internal intercostal muscles. These findings indicate that the response pattern observed in the enzyme activities studied following training are to some degree specific to the respiratory muscle investigated.

Metabolic and contractile properties of rabbit muscles: a statistical approach

The metabolic and contractile properties of rabbit muscles representative of the three main muscle types have been studied. A statistical analysis of the results indicates the more discriminant variables for this characterization and shows in particular that the myosin light chains represent a very significant discriminant factor of the muscular type. Results also show that lactate dehydrogenase activity is strongly correlated with the percentage of lactate dehydrogenase M-subunit and with myosin light chains.

Effects of training and methandrostenolone (an anabolic steroid) on energy metabolism in the guinea pig: changes in enzyme activities in gastrocnemius muscle and myocardium

Modifications of enzyme activities (creatine kinase and its B subunit; adenylate kinase; hexokinase; phosphofructokinase; lactate dehydrogenase; malate dehydrogenase, isocitrate dehydrogenase; citrate synthase; acetylcarnitine transferase; beta-hydroxyacetyl-CoA dehydrogenase; cytochrome c oxidase) in gastrocnemius muscle and myocardium were reported after two forms of training with or without administration of anabolic steroid. Endurance training was on a horizontal motor-driven treadmill, 2 km X hr-1, 5 days a week for 0.5 hr per day for 5 weeks. In the case of power endurance training there was a slope of 45 degrees. Enzyme activities in controls and treated guinea pigs, as well as treatment-induced enzyme activity changes are time dependent. Some of these activities correlate linearly with one another; such correlations characterize the effect of adaptation. Endurance training and power endurance training in this study induce similar modifications and seem to differ essentially in the daily work load. The anabolic steroid methandrostenolone (dianabol) induces modifications which training does not bring about but which training at least partially eliminates.

Trophic effect of the sympathetic nervous system on vascular smooth muscle

While the vasomotor effect of the sympathetic nervous system (SNS) on the arterial wall is well recognized, its trophic function is not. It is the aim of these studies to demonstrate this all-important function as it relates to the vascular muscle. Although the exact mechanism by which sympathetic nerve impulses influence the metabolism of the vessel wall is unknown, effects of sympathectomy can be demonstrated. Several lines of evidence indicate that chronic absence of sympathetic innervation in rabbits increases collagen synthesis and decreases activity of tricarboxylic acid cycle enzymes in the vascular wall. When chemically sympathectomized rabbits were fed a 1% cholesterol dietary supplement for 80 days, the aortas of these rabbits contained significantly more cholesterol and total lipids than those from fully innervated controls in spite of insignificant differences in plasma lipids. In a subsequent series of experiments we analyzed the efficacy of the SNS in two strains of pigeons. White Carneau (WC) pigeons are known by the susceptibility to atherosclerosis of the aorta while Show Racer (SR) pigeons are not. Our results demonstrate that the abdominal aorta of WC pigeons has less sympathetic innervation and it declines faster with age than that of SR pigeons. The results of the described studies documenting the direct trophic influence of the SNS on the arterial wall are reinforced by the similarity to the vessel wall changes induced by partial sympathectomy and natural ageing.

Metabolic meaning of elevated levels of oxidative enzymes in high altitude adapted animals: an interpretive hypothesis

It is commonly observed that during acclimatization to altitude oxidative enzyme activities increase per g wet weight of tissue. To examine this problem in long-term adapted animals we measured citrate synthase (CS), hydroxyacylCoA dehydrogenase (HOAD), pyruvate kinase (PK), and lactate dehydrogenase (LDH) activities/g of myocardium in two domestic species (llama and alpaca) and a high altitude deer, the taruca. In all these species, we found an upward scaling of oxidative capacity (indicated by absolute activities of CS and HOAD) but a downward scaling of anaerobic/aerobic metabolic potentials of the heart (indicated by low ratios of LDH/CS, and LDH/HOAD, but high ratios of PK/LDH). As the direction and magnitude of these long-term adaptations are the same as in shorter-term acclimatizations, we wondered why a similar pattern at the enzyme level correlates with the right shift of the O2 dissociation curve (ODC) in the latter case, but with a left shifted ODC in the former. We hypothesize that in the long term, increased oxidative enzyme activities allow increased maximum flux capacity of aerobic metabolism. This in turn calls for physiological adjustments in O2 transfer systems; flux limits of the former must be matched by flux limits of the latter. Only then can an acceptably high scope for aerobic activity be achieved despite reduced O2 availability in inspired air. Such long-term match-up invariably calls for a left-shifted ODC plus other well known adjustments in O2 transport. In the short term, right shifting the ODC may increase the total amount of aerobic work possible (by favoring O2 unloading and thus raising tissue O2 concentration), yet maximum flux capacity cannot be changed much because mitochondrial metabolism is designed for maintaining stable rates of ATP synthesis even at widely varying O2 tensions. That is why even in short-term acclimatization, in order to increase flux capacity, the activities of oxidative enzymes also must be increased.

Changes in muscle esterases in genetically dystrophic and control littermate mice

The hypothesis that the existence of a family of isoenzymes is at the basis of the heterogeneity of esterase activity among skeletal muscles from dystrophic Re 129J and control littermate mice was tested using isoelectrofocusing (IEF) in polyacrylamide gel. All muscles considered showed not only quantitative heterogeneity, as previously observed in this laboratory, but also qualitative differences with regard to their esterase isoenzymes. Differences in the number and the relative amounts of isoenzymatic bands were found between different muscles from both control and dystrophic animals. In most dystrophic muscles a new isoenzymatic band appeared at pH 6.6. Another band, identified at pH 5.12, was more pronounced in dystrophic than in control muscles. The specificity of these observations is indirectly supported by the fact that other tissue, such as heart, liver, and kidney, did not show the quantitative or qualitative abnormality present in the dystrophic skeletal muscles.

Metabolic types of muscle in the sheep: I. Myosin ATPase, glycolytic, and mitochondrial enzyme activities

The metabolic characteristics of 12 skeletal muscles of the sheep were studied. Glycolytic activities (hexokinase, glycogen synthetase I and D, phosphorylase a and b, phosphofructokinase) were measured. Myofibrillar ATPase activity was evaluated. Oxygen consumption, respiratory control and carnitine palmityl transferase, isocitrate dehydrogenase, succinate dehydrogenase and cytochrome oxidase activities were measured in isolated mitochondria. Three metabolic types could be distinguished; (1) essentially oxidative slow twitch muscles, typified by the supraspinatus and infraspinatus, having low ATPase activity, (2) fast twitch red muscles, typified by the longissimus dorsi and the semimembranosus, having a higher ATPase activity and both high oxidative and high glycolytic activity, and (3) essentially glycolytic fast twitch muscles, typified by the tensor fascia lata and the semitendinosus, having the highest ATPase activity.

Enzyme levels in individual rat muscle fibers

Individual muscle fibers from the rat anterior tibialis and soleus muscles were each analyzed in duplicate for lactate dehydrogenase (LDH, EC 1.1.1.27), malate dehydrogenase (MDH, EC 1.1.1.37), 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35), fumarate hydrotase (EC 4.2.1.2), glycogen phosphorylase (EC 2.4.1.1), 6-phosphofructokinase (EC 2.7.1.11), pyruvate kinase (EC 2.7.1.40), fructose-bisphosphatase (EC 3.1.3.11), and creatine kinase (EC 2.7.3.2). A few fibers were also analyzed for adenylate kinase (EC 2.7.4.3). In general, there was a wide and almost continuous spectrum of coordinated enzyme activities. In the tibialis muscle, two fiber groups could be clearly distinguished on the basis of MDH activity. The high MDH group had on the average lower LDH activity, but there was a great deal of overlap in LDH between the two groups. Less overlap was observed for phosphorylase and fructose-bisphosphatase, both inversely related to MDH. Only one main group of fibers (presumably slow twitch) was found in the soleus muscle, although enzyme activities also covered a wide range. These soleus fibers were clearly distinguished from the high MDH tibialis group by much lower activities of LDH, pyruvate kinase, and fructose-bisphosphatase.

Enzyme histochemical studies on the conducting system of the human heart

In this communication, the results of applying various histochemical techniques for the localization of oxidoreductases, transferases, hydrolases and isomerases in the human heart are presented. The Purkinje fibres of the atrioventricular conducting system of the human heart differ from the myocardium proper in containing a slightly higher activity of most of the glycolytic and gluconeogenetic enzymes investigated. The relatively higher activity of 6-phosphofructokinase, the key enzyme in anaerobic carbohydrate metabolism, is especially noteworthy. On the other hand, the activities of some of the enzymes that play a part in the aerobic energy metabolism is slightly less than those in the myocardium fibres. As for the activity of the NADPH regenerating enzymes, the activity of 6-phosphogluconate dehydrogenase and malate dehydrogenase (oxaloacetate-decarboxylating) is somewhat higher, and the activity of glucose-6-phosphate dehydrogenase similar, in the Purkinje fibres compared to that in the myocardial fibres. The activity of myosin ATPase is similar for both types of fibre. Likewise, the fibres of the conducting system and of the myocardium show a similar activity of acid phosphatase, beta-glucuronidase, non-specific naphthylesterase and peroxidase. The neurogenic function of the conducting system of the human heart was demonstrated by the high activity of acetylcholinesterase in the Purkinje fibres and in the atrioventricular node. All these histochemical findings in Purkinje fibres are similar at widely differing levels of the conducting system.

Inhibition by (aminooxy)acetate of the malate-aspartate cycle in the isolated working guinea pig heart

The quantitative importance of the malate-aspartate cycle and the sn-glycerol 3-phosphate cycle, with respect to the flux of cytosolic reducing equivalents across the mitochondrial membrane, was studied in isolated perfused guinea pig hearts. The heart preparations performed pressure-volume work and metabolized glucose, lactate, pyruvate or 3-hydroxybutyrate. With glucose or lactate as the substrate, (aminooxy)acetate, an inhibitor of the malate-aspartate cycle, caused left ventricular failure, manifested by reduced aortic pressure and cardiac output, in association with a decrease in myocardial oxygen consumption and a depletion of high energy phosphate stores; lactate and particularly sn glycerol 3-phosphate accumulated in the myocardium. Moreover, lactate release rates increased more than 10-fold in presence of glucose and (aminooxy)acetate. Pretreatment of the animals with high doses of triiodothyronine did not prevent the hemodynamic and metabolic alterations caused by (aminooxy)acetate. In contrast, (aminooxy)acetate did not affect performance and energy-yielding metabolism when hearts metabolized pyruvate or 3-hydroxybutyrate as the substrate. From the findings it is concluded that the malate-aspartate cycle preponderates over the sn-glycerol 3-phosphate cycle in the working guinea pig heart, even when sn-glycerol 3-phosphate accumulates.

Metabolic heterogeneity of muscle fibers classified by myosin ATPase

Muscle fibers are commonly classified histochemically into three types by the staining intensity for myosin ATPase combined with those for metabolic enzymes. Preincubation at pH 4.6 gives rise to three staining intensities of myosin ATPase which are also used for fiber typing. The two classification systems were compared by computer analysis of the individual staining profiles of over 2,500 fibers, and found not to be equivalent. The analysis showed metabolic heterogeneity among the fiber groups distinguished according to their differences in myosin ATPase.

Turnover rates of hexokinase I, phosphofructokinase, pyruvate kinase and creatine kinase in slow-twitch soleus muscle and heart of the rabbit

Hexokinase I was purified from rabbit heart to a specific activity of 70 U/mg protein. The purified enzyme was electrophoretically homogeneous with an apparent molecular weight of 102,000. Purified immunoglobulins from sheep were used to titrate the percentage of hexokinase I in various tissues of the rabbit. Precipitating antibodies from sheep were also prepared against rabbit muscle MM-creatine kinase, phosphofructokinase and pyruvate kinase. Apparent turnover rates of these phosphotransferases and of hexokinase I were determined in rabbit heart and soleus muscle by means of the immunoprecipitation technique after single pulse labelling with [U-14Cl]leucine in vivo. Apparent half-lives of phosphofructokinase, pyruvate kinase and hexokinase I were 0.56 d, 0.73 d and 0.93 d in rabbit heart. In slow-twitch soleus muscle half-lives of phosphofructokinase, pyruvate kinase, hexokinase II and creatine kinase were 0.63 d, 0.72 d, 0.85 d and 0.82 d. The similarity of the rate constants of degradation of these enzymes is interpreted as an indication that different tissue concentrations result primarily from different rates of synthesis.

Molecular transformations in sarcoplasmic reticulum of fast-twitch muscle by electro-stimulation

Chronic electro-stimulation of fast-twitch rabbit muscle with the frequency pattern received by a slow-twitch muscle induces a progressive transformation of the sarcoplasmic reticulum. After 2 days stimulation activities of Ca2+-dependent ATPase and of Ca2+ transport begin to decrease, and are paralleled by a progressive decrease in Ca2+-dependent and Ca2+, Mg2+-dependent phosphoprotein formation, reduced rate of dephosphorylation and a rearrangement of the electrophoretic polypeptide and phosphoprotein patterns. These findings suggest a transformation of the sarcoplasmic reticulum to resemble that of a slow-twitch muscle. This transformation is paralleled by increase in time-to-peak of twitch contraction and half relaxation time and occurs before conversion of the myosin light chain pattern is observed. The parallel time course of changes in contractile properties of stimulated muscle and the molecular and functional properties of the sarcoplasmic reticulum emphasizes the definitive role of the latter in determining the twitch characteristics of fast and slow twitch muscles.