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The purpose of this study was to determine whether an epinephrine (Epi) infusion would enhance muscle glycogenolysis during intense aerobic exercise. Epi was infused at rates that produced the same plasma Epi concentrations observed after caffeine (Caf) ingestion. Seven male subjects cycled for 15 min at 80% maximal O2 uptake during four different trials. Trial 1 was preceded by a 9 mg/kg oral dose of Caf to determine resting and exercise plasma Epi concentrations. Trial 2 was used to determine the Epi infusion rates needed to mimic the plasma Epi levels found with Caf. Trials 3 and 4 were randomized and consisted of either an Epi infusion or a saline infusion (control, Con). During Epi and Con trials muscle samples were obtained from the vastus lateralis at 0, 3, and 15 min of exercise. Plasma Epi levels were similar between Caf and Epi and were elevated twofold compared with Con. At 5 min of exercise the plasma Epi concentrations were 1.51 +/- 0.26, 2.61 +/- 0.34, and 2.97 +/- 0.45 nM for the Con, Caf, and Epi trials, respectively. Plasma Epi increased to 3.08 +/- 0.56, 5.45 +/- 1.11, and 5.86 +/- 1.03 nM at 14 min of exercise in the Con, Caf, and Epi trials, respectively. Muscle glycogenolysis was not different between trials (Con 220.5 +/- 25.3 vs. Epi 240.6 +/- 12.1 mmol/kg dry muscle). In addition, the degradation of muscle ATP and phosphocreatine and the accumulation of muscle lactate, ADP, and AMP were similar between trials.(ABSTRACT TRUNCATED AT 250 WORDS)

To investigate the effects of renal transplantation (Rtx) on the nutritional status, muscle composition and the plasma and muscle free amino acid (AA) pattern, three groups of altogether 30 renal transplant patients (group I n = 10; 46 +/- 14 [SD] days after Trx), (group II n = 10; 13 +/- 2 months after Rtx) and (group III n = 10; 9 +/- 2 years after Rtx) underwent anthropometric measurements, blood sampling and percutaneous muscle biopsy. The immunosuppressive therapy consisted of prednisolone, azathioprine and cyclosporine-A. The results were compared with data from age-matched healthy subjects. Renal function was impaired in groups I, II and III. Serum albumin was decreased in groups I and II. The patients of group II had an increased percentage of body fat, triceps and subscapular skin folds and total sum of skinfolds. In group I the ratio alkaline-soluble protein (ASP) to DNA, which is a sensitive index of protein depletion on the cellular level, was decreased. Muscle magnesium content was decreased whereas the muscle DNA, sodium and chloride contents were increased. The mean plasma concentration of most essential AA (EAA) was essentially normal except phenylalanine which was increased in groups I and II.(ABSTRACT TRUNCATED AT 250 WORDS)

New techniques to extract natural gas from unconventional resources have become economically competitive over the past several years, leading to a rapid and largely unanticipated expansion in natural gas production. The US Energy Information Administration projects that unconventional gas will supply nearly half of US gas production by 2035. In addition, by significantly expanding and diversifying the gas supply internationally, the exploitation of new unconventional gas resources has the potential to reshape energy policy at national and international levels—altering geopolitics and energy security, recasting the economics of energy technology investment decisions, and shifting trends in greenhouse gas (GHG) emissions. In anticipation of this expansion, one of the perceived core advantages of unconventional gas—its relatively moderate GHG impact compared to coal—has recently come under scrutiny. In this paper, we compare the GHG footprints of conventional natural gas, unconventional natural gas (i.e. shale gas that has been produced using the process of hydraulic fracturing, or ‘fracking’), and coal in a transparent and consistent way, focusing primarily on the electricity generation sector. We show that for electricity generation the GHG impacts of shale gas are 11% higher than those of conventional gas, and only 56% that of coal for standard assumptions.

We present a newborn boy who died after 53 days of life in respiratory failure with lactic acidosis. Analysis of skeletal muscle mitochondria demonstrated a combined defect in complexes I and IV of the respiratory chain. The boy had severe muscle hypotonia but no signs of encephalopathy, illustrating the variation in multi-organ presentation of mitochondrial defects.

Seven subjects cycled to exhaustion [58 +/- 7 (SE) min] at approximately 75% of their maximal oxygen uptake (VO2max). Needle biopsy samples were taken from the quadriceps femoris muscle at rest, after 3, 10, and 40 min of exercise, at exhaustion, and after 10 min of recovery. After 3 min of exercise, a nearly complete transformation of the pyruvate dehydrogenase complex (PDC) into active form had occurred and was maintained throughout the exercise period. The total in vitro activated PDC was unchanged during exercise. The muscle concentration of acetyl-CoA increased from a resting value of 8.4 +/- 1.0 to 31.6 +/- 3.3 mumol/kg dry wt at exhaustion and that of acetylcarnitine from 2.9 +/- 0.7 to 15.6 +/- 1.6 mmol/kg dry wt. This was accompanied by corresponding decreases in reduced CoA (CoASH) from 45.3 +/- 3.1 to 25.9 +/- 3.1 mumol/kg dry wt and in free carnitine from 18.8 +/- 0.7 to 5.7 +/- 0.5 mmol/kg dry wt. Acetyl group accumulation, in the form of acetyl-CoA and acetylcarnitine, was maintained throughout exercise to exhaustion while the glycogen content decreased by 90%. This suggests that availability of acetyl groups was not limiting to exercise performance despite the nearly total depletion of the glycogen store. The increased acetyl-CoA-to-CoASH ratio during exercise caused inhibition of neither the PDC transformation nor the calculated catalytic activity of active PDC.

This study was designed to examine the effects of stimulation and fat availability on the contents of acetyl coenzyme A (acetyl-CoA), free CoA (CoASH), acetylcarnitine, and free carnitine in the oxidative fiber types of rat skeletal muscle. Hindlimb muscles were perfused with no exogenous free fatty acids (FFA) or high FFA (0.93 +/- 0.03 mM) for 10 min at rest and during isometric, tetanic stimulation. Soleus (SOL) and red gastrocnemius (RG) muscles were sampled prior to perfusion and following rest perfusion and 1 and 5 min of stimulation. The SOL muscle contains predominantly slow oxidative (SO) fibers and the RG contains 56% fast oxidative-glycolytic (FOG) and 35% SO fibers. O2 uptake and tetanic tension production were similar in the fat-free and high FFA treatments. Rest perfusion with high FFA increased acetyl-CoA from 14.6 +/- 1.0 to 20.1 +/- 2.5 nmol/g dry muscle (dm) and acetylcarnitine from 0.12 +/- 0.01 to 0.78 +/- 0.18 mumol/g dm in the RG, while fat-free perfusion had no effect. The SOL results were similar as high FFA increased acetyl-CoA from 7.7 +/- 1.0 to 14.2 +/- 3.1 nmol/g dm and acetylcarnitine from 0.14 +/- 0.02 to 0.49 +/- 0.09 mumol/g dm. Stimulation increased acetyl-CoA and acetylcarnitine to values above rest in SOL and RG in both treatments and removed all fat-free and high-fat differences. The decreases in CoASH and free carnitine were reciprocal to the increases in acetyl-CoA and acetylcarnitine at all time points in both muscles such that total CoA and carnitine were constant.(ABSTRACT TRUNCATED AT 250 WORDS)

We examined the effects of a high-caffeine dose on endurance performance and muscle acetyl group metabolism during prolonged exercise. Eight subjects cycled to exhaustion at approximately 80% maximal oxygen uptake (VO2max) 1 h after ingestion of 9 mg/kg body wt dextrose (Pl) or caffeine (Caf). In the Pl trial, muscle biopsies were taken at rest (1 h postingestion) and at 15 min and exhaustion during exercise. The Caf trial followed the same protocol 1 wk later, with an additional biopsy at the time corresponding to Pl exhaustion. The subjects cycled significantly longer during the Caf trial (96.2 +/- 8.8 min) than in the Pl trial (75.8 +/- 4.8 min). Net glycogenolysis during the initial 15 min of cycling was reduced in the Caf vs. Pl trial (4.7 +/- 1.5 vs. 10.6 +/- 1.3 mmol.kg dry muscle-1.min-1; P less than 0.05). Muscle citrate concentration was increased at rest with Caf (0.59 +/- 0.07 vs. 0.37 +/- 0.05 mmol/kg dry muscle; P less than 0.05) but increased to similar values in both trials during cycling. Caf elevated the acetyl-CoA/CoA-SH ratio at rest (0.316 +/- 0.046 vs. 0.201 +/- 0.023; P less than 0.05) but had no effect on the increases in muscle acetyl-CoA and acetylcarnitine during exercise. The results indicate that Caf before exercise decreased muscle glycogenolysis by approximately 55% over the first 15 min of exercise at approximately 80% VO2max. This "spared glycogen" was available late in exercise and coincided with a prolonged time to exhaustion. Increased utilization of intramuscular triacylglycerol and/or extramuscular free fatty acids after caffeine ingestion may inhibit carbohydrate use at rest and early during exercise via elevations in muscle citrate and the acetyl-CoA/CoA-SH ratio. Muscle acetyl-CoA and acetylcarnitine were maintained above resting contents even at exhaustion when muscle glycogen was depleted.

It has previously been shown that cobalt accumulates in the myocardium of rats, mainly the sarcoplasmic reticulum (SR) and the mitochondrial inner membrane. In order to investigate the mode of accumulation of cobalt in the SR, rats were given a dietary cobalt supplementation of 40 mg of CoSO4 x 7H2O kg-1 body wt, after which the rats were sacrificed and the sarcoplasmic reticulum was isolated. The SR proteins were subjected to analysis by polyacrylamide gel electrophoresis followed by protein staining and determination of the content of cobalt in each protein band. The major cobalt-binding protein was found to have a molecular weight of about 100,000; a 200,000 molecular weight protein was also found to bind cobalt, although less extensively. These results suggest that cobalt is bound to the monomeric and dimeric forms of Ca(2+)-ATPase in the SR of the myocardium.

The degradation of adenosine triphosphate, phosphocreatine and glycogen was determined in type I and type II fibres of the human quadriceps femoris muscle during intermittent electrical stimulation at 20 and 50 Hz, (1.6 seconds stimulation, 1.6 seconds rest). Seven healthy volunteers took part in the study. Muscle biopsy samples were obtained at rest and after 10 and 20 seconds of stimulation (six and 12 contractions, respectively). The resting contents of adenosine triphosphate, phosphocreatine and glycogen were all higher (P less than 0.05) in type II fibres compared to type I fibres. By the end of stimulation, whole muscle force production had declined to 84 and 77% of the initial force at 20 and 50 Hz, respectively. The phosphocreatine degradation rate for 10 and 20 seconds of stimulation was greater in type II fibres (P less than 0.05) compared to type I fibers at both 20 and 50 Hz. The rates of glycogenolysis after 20 seconds stimulation in type II fibres were 3.18 +/- 1.1 and 6.31 +/- 1.39 mmol glycosyl units kg-1 s-1. The corresponding rates in type I fibres were 0.46 +/- 0.73 and 0.60 +/- 0.39 mmol glycosyl units kg-1 s-1, which were not significantly different from zero. It is hypothesized that the decline in whole muscle force observed during electrical stimulation may be a consequence of the rapid loss of PCr stores in type II fibres.

Firm decisions to invest in low-carbon projects in developing countries: the influence of climate policy and evolving carbon markets Nathan Hultman(1, 3, 4), S Pulver(2) (1) University of Maryland, School of Public Policy , College Park, MD, USA (2) Brown University, Providence, RI, USA (3) Joint Global Change Research Institute, College Park, MD, USA (4) Martin Institute for Science & Civilization, University of Oxford, UK

A radioactive assay for the determination of pyruvate dehydrogenase complex activity in muscle tissue has been developed. The assay measures the rate of acetyl-CoA formation from pyruvate in a reaction mixture containing NAD+ and CoASH. The acetyl-CoA is determined as [14C]citrate after condensation with [14C]-oxaloacetate by citrate synthase. The method is specific and sensitive to the picomole range of acetyl-CoA formed. In eleven normal subjects, the active form of pyruvate dehydrogenase (PDCa) in resting human skeletal muscle samples obtained using the needle biopsy technique was 0.44 +/- 0.16 (SD) mumol acetyl-CoA.min-1.g-1 wet wt. Total pyruvate dehydrogenase complex (PDCt) activity was determined after activation by pretreating the muscle homogenate with Ca2+, Mg2+, dichloroacetate, glucose, and hexokinase. The mean value for PDCt was 1.69 +/- 0.32 mumol acetyl-CoA.min-1.g-1 wet wt, n = 11. The precision of the method was determined by analyzing 4-5 samples of the same muscle piece. The coefficient of variation for PDCa was 8% and for PDCt 5%.

1. A method is described enabling the determination of fat, water, electrolytes, protein, DNA, RNA and total creatine in a single sample of human muscle obtained by the percutaneous needle-biopsy technique. The amino acid content can also be analysed in the same muscle sample. 2. Fifty healthy subjects were studied: 29 between 19 and 40 years of age, 11 between 41 and 60 years of age, and 10 between 61 and 85 years of age. The two groups aged less than 60 years showed only marginal differences in muscle composition, whereas the highest age group showed increases in muscle fat content in relation to tissue weight and decreases in alkali-soluble protein content in relation to both tissue weight and tissue DNA content. Also, potassium, magnesium, total creatine and RNA contents were decreased in this age group when related to tissue DNA content. When alkali-soluble protein was used as a reference base, only magnesium content was decreased. 3. A comparison was also made between female (n = 23) and male (n = 18) subjects in the age groups below 60 years. Differences observed included a higher fat content in female muscle, and an increase in total creatine content in relation to tissue weight. The alkali-soluble protein content was lower per muscle cell in the females when calculated on the basis of DNA content. 4. The results show that in the assessment of muscle constituents, age and sex must be taken into account.

Nutritional status was assessed in 25 anemic hemodialysis patients before and during erythropoietin treatment. Nutritional assessment included regular blood chemistry determinations, anthropometric measurements, analysis of protein content in skeletal muscle, and estimation of daily protein intake from protein catabolic rate determinations (using urea kinetic modelling) and dialysis efficiency for urea. These measurements were done immediately prior to erythropoietin treatment, after anemia correction and after one year of maintenance erythropoietin treatment. Both relative body weights and subcutaneous fat stores were low at the start, but increased significantly (p less than 0.05) during the study. Sixteen of the 25 patients gained weight and eight patients lost weight. The patients with weight gain had at the start of the study low weight indices (body weight 89.9 +/- 7.6% of ideal body weight, body mass index 20.6 +/- 1.6), significantly (p less than 0.005) lower than the patients with weight loss. Although protein malnutrition was not obvious from arm anthropometrics, alkali soluble protein/DNA ratio or from serum albumin determinations, ASP/DNA ratio, increased in three of five patients investigated after one year on erythropoietin treatment. Neither protein catabolic rate nor dialysis efficiency changed significantly during the study. We conclude that anemia correction with erythropoietin has a positive effect on malnutrition in hemodialysis patients. In patients with underweight, an adjustment of fat stores was initially observed, followed possibly by an improvement in muscle protein content.

The concentrations of glycogen, ATP, and phosphocreatine were analyzed in types I and II muscle fibers separated from biopsy samples of the quadriceps femoris muscle in five healthy volunteers. Muscle samples were obtained before and after 64 s of intermittent electrical stimulation. The experiment was carried out without and with epinephrine (Epi) infusion. Before stimulation the glycogen concentration was 11% higher in type II than in type I fibers (P less than 0.05). During electrical stimulation, rapid glycogenolysis occurred in type II fibers with hardly any detectable glycogenolysis in type I fibers. The calculated rates of glycogenolysis were 0.18 +/- 0.14 and 3.54 +/- 0.53 mmol glucose.kg dry muscle-1.s-1 in types I and II fibers, respectively. Epi infusion increased the rate of glycogenolysis during electrical stimulation in type I fibers (10-fold) but did not enhance the rate in type II fibers (P greater than 0.05). It is considered that, during short-term maximal muscle contraction, rapid muscle glycogenolysis occurs predominantly in type II fibers even though types I and II fibers are recruited and that, when Epi stimulation of glycogenolysis occurs, this is predominantly limited to type I fibers.

Force and relaxation were measured during electrical stimulation of the quadriceps muscle of 14 volunteers. Stimulation produced 51.2 s of intermittent ischaemic contractions either as 16 3.2-s tetani or as 64 0.8-s tetani. Changes during recovery were followed for 180 s. On 8 subjects muscle biopsies were taken during work and after the rest period for determination of ATP, phosphocreatine and intermediates in glucolysis. The stimulation using 0.8-s contractions gave more pronounced fatigue and slowing of relaxation. There was a good correlation between force and relaxation during work but this relation changed during recovery, indicating that no general relation exists between these two contraction characteristics. In the 0.8-s stimulation more ATP was utilized and there were more profound changes in metabolite levels. We found a correlation between estimated [H2PO4−] and relaxation covering both work and recovery and hypothesize that inorganic phosphate and its removal by phosphocreatine resynthesis during recovery might be important. Since stimulation patterns differ in force and relaxation even after the recovery period we suggest that additional factors, such as pH, are of importance in this work model.

Nuclear power is an opaque, technologically complex, and—let's be forthright—potentially hazardous way to generate electricity. Because of these characteristics, some people will always view the technology with skepticism or suspicion and argue that the benefits are not worth the risks. In addition, in part because nuclear power presents many potential benefits, there will always be others, usually with more thorough technical expertise, who see it as an obviously elegant solution to major energy and climate constraints and whose risks are relatively small and manageable. These well-worn and arguably defensible perspectives have infused and colored the past few decades of public policy discourse—particularly in the US and some European countries—on nuclear power as part of global energy supply. The pressing constraints of anthropogenic climate change, regional air quality in growing cities, and volatile resource prices, however, raise the appropriate question of how much nuclear power might reasonably contribute in a future global energy portfolio.

Percutaneous electrical stimulation was used to study the force response of the quadriceps muscle. The normal frequency dependence of force was investigated in muscles at rest and after fatiguing contractions. A comparison between force response during fatigue induced by electrical stimulation at different frequencies and by voluntary work suggested equal changes in contractility, irrespective of the fatigue-inducing procedure. In fresh muscle we found a linear relation between stimulation period (10–100 ms) and force. At fatigue the relation changes with maximal deviation from linearity at a 50-ms period (20 Hz). There is a rapid recovery of high frequency force whereas the low frequency response remains low even after 30 min rest. At very low frequencies there is initially unexpectedly high force in fatigued muscle. This could be a result of increased fusion of twitches with initially prolonged relaxation time. To study the twitch summation we compared experimental results in a wide frequency range with computer-simulated twitch summations and present the frequency dependence of summation processes in human quadriceps muscle.

The control mechanism of glycogenolysis by phosphorylase a in contracting muscle has been investigated. The quadriceps femoris muscles of six subjects were intermittently stimulated at 15 and 50 Hz. The stimulation lasted 9.6 s and was performed twice at 15 Hz and once at 50 Hz. Epinephrine was infused continuously during the experiment. The force generation and ATP turnover rate were nearly twofold higher at 50 Hz than at 15 Hz. Calculated mean Pi was 5.7 and 10.0 mM during the two 15-Hz stimulations and 8.1 mM during the 50-Hz stimulation. Phosphorylase a varied between 85.5 and 91.5% without significant differences between periods. However, the rate of glycogenolysis was twofold higher during the stimulation at 50 Hz than it was at 15 Hz (P less than 0.05) and was related to the ATP turnover rate (r = 0.992). These results demonstrate that rapid glycogen breakdown during muscle contraction cannot be solely explained by transformation of phosphorylase b to a and increased Pi concentration. The contraction intensity may determine the glycogenolytic rate through a transient increase in free AMP level related to the ATP turnover rate.

The ATP content was measured in type I and type II fibres from human vastus lateralis muscle at rest, after electrical stimulation and during recovery. At rest the mean values were 25.2 +/- 4.02 and 25.9 +/- 3.62 mmol kg-1 dry muscle (mean +/- SD) for type I and type II fibres respectively. Normal distribution curves were found for both types I and II fibres. After intermittent electrical stimulation for 83 s (1.6 s stimulation, 1.6 s pause) with occluded blood flow, the force generation decreased to 22% of the initial value and the muscle tissue showed a mean decrease in ATP to 14.8 and in phosphocreatine to 5.44 mmol kg-1 dry muscle; lactate increased to 128.9 mmol kg-1 dry muscle. The ATP content in isolated fibres was equally decreased in both fibre types to 16 mmol kg-1 dry muscle. In 11% of the fibres the ATP content was lower than 10 mmol kg-1 dry muscle. After 15 min rest with intact blood circulation ATP was completely resynthesized in type I fibres and to 91% in type II fibres.

Treadmill exercise of 2-min duration and increasing intensity resulted in increased formation of acetyl-CoA and acetylcarnitine in working muscle of Thoroughbred horses. At high work intensities a plateau was reached for both acetyl-CoA (approximately 50 mumols/kg dry muscle) and acetylcarnitine (approximately 20 mmol/kg dry muscle). Postexercise concentrations were significantly (P less than 0.001) correlated; [acetylcarnitine] = 349.[acetyl-CoA] + 2.4. The results indicate that approximately 350 mumols acetylcarnitine were accumulated for every 1 mumol acetyl-CoA. Under the conditions of exercise used it is probable that most of the acetyl-CoA formed is generated through the intramitochondrial decarboxylation of pyruvate. The acetyl groups of acetyl-CoA are apparently redistributed throughout the whole cell through formation of acetylcarnitine, which readily transverses the mitochondrial membrane. Despite the redistribution, however, the close correlation between acetylcarnitine and acetyl-CoA would indicate that equilibrium was maintained and that neither acetylcarnitine transferase nor carnitine/acetylcarnitine translocase were rate limiting. There is some question as to whether the changes observed relate directly to exercise itself or to the state in muscle 10 s or more after exercise.

Cobalt has been shown to accumulate in the myocardium of uraemic patients and has been suggested as a myocardial toxin inhibiting mitochondrial respiration. In order to study the cellular effects of cobalt exposure three groups of rats (n = 12 per group) were fed a diet containing 12% protein without supplementation or with 20 mg and 40 mg CoSO4 7 H2O/kg body weight/day respectively. After 8 weeks the hearts and soleus muscles were removed. Cobalt in tissues and in four cell fractions were analysed with neutron-activation analysis (ng/g wet weight and ng/mg protein respectively). Mitochondrial respiration was analysed as ATP-production rate using pyruvate + malate and palmitoyl-carnitine + malate as substrate. The ATP-production from pyruvate + malate was unchanged in both heart and skeletal muscle in the exposed animals. With palmitate as substrate, the heart muscle showed a slightly lower ATP-production rate (p less than 0.05) after the 20 mg cobalt dose, but the rate was unchanged in the group with higher cobalt intake. No changes in ATP-production rate from palmitate was observed in soleus muscle. The microsomal (100,000 g) fraction in the myocardial cells contained significantly higher cobalt concentrations compared to the mitochondrial fraction in both the unexposed (1.4 ng/mg protein vs 0.19, p less than 0.05) and exposed rats (53.4 ng/mg protein vs 13.2, p less than 0.005). In conclusion, cobalt showed a large accumulation in myocardial cells, without significant effects on mitochondrial ATP-formation rate from oxidation of pyruvate or palmitate and with the highest cobalt content contained in the microsomal (100,000 g) fraction.

1. Muscle buffering capacity (beta m) and dipeptide content were measured in locomotory muscles of the Thoroughbred horse, Greyhound dog and Man. 2. Beta m and carnosine contents were highest in the horse. Anserine was only found in dog muscle. 3. The higher beta m in horse and dog muscle, compared with man, appears to be predominantly due to higher muscle contents of histidine containing dipeptides in these species.

As countries begin to reassess and expand their energy research and development programs, it is appropriate to understand the likely costs of alternate approaches. Unfortunately, communities of experts have a well-known optimistic bias in their judgments. We review findings from several disciplines that underscore this tendency toward overconfidence as well as some proposed alternatives to incorporate it in public decision-making. We further argue, based on a disaggregated analysis of US nuclear power costs, that incorporating a second-order uncertainty in the shape of the distribution of cost components is essential for capturing important elements of uncertainty in moving forward with expanded energy R&D programs.

Disagreement over principles for the inclusion of developing countries in future global greenhouse gas caps remains an obstacle to the ratification and implementation of the Kyoto Protocol. [ Baer et al. ][1] argue that a transition from allocations based on past emissions (with a "grandfather clause"), such as the Kyoto Protocol, embodies for the industrialized nations, to allocations a new regime based on equal per capita emissions rights, is a necessary and fair solution that can lead to an effective global reduction regime. Such an allocation is consistent with numerous ethical principles and legal precedents, could facilitate trading in emissions permits, and can be implemented through a transitional period that accommodates the different situations and emissions levels of various countries. [1]: http://www.sciencemag.org/cgi/content/full/289/5488/2287

In order to evaluate different methods of estimating intracellular content of potassium, determinations of potassium were made in erythrocytes, in muscle biopsy specimens and in the total body. The total body potassium (TBK) was related to body weight (Bwt), lean body mass (LBM), dry LBM, soft fat-free solids (SFFS), total body water (TBW) and calculated intracellular fluid (ICF). Sixty-two healthy subjects and 80 patients with various diseases and therapy known to influence the potassium metabolism were studied. Statistically significant correlations were found between potassium content in muscle biopsies related to fat-free solids and TBK/Bwt (r = +0.56, P less than 0.05), TBK/LBM (r = + 0.58, P less than 0.01), dry LBM (r = + 0.54, P less than 0.05) and TBK/SFFS (r = + 0.68, P less than 0.01). A correlation was found between muscle potassium related to intramuscular water and TBK/TBW (r = + 0.47, P less than 0.05). No correlations were found between EK and TBK/LBM, TBK/dry LBM or TBK/ICF. Between EK and serum potassium a negative correlation (r = -0.31, P less than 0.05) was found in a group of untreated hypertensives. It is concluded that the quotients of TBK (TBK/LBM, TBK/TBW and TBK/SFFS) might be used in the study of intracellular potassium--at least in the study of patient groups.

Phosphorylase activity, glycogenolytic and glucolytic rates were estimated in human quadriceps muscle during electrical stimulation at 20 Hz. Two stimulation periods of 10 s duration were separated by a pause of 60 s. The blood circulation to the leg was intact or occluded during the experiment. ATP turnover rates and force production were of the same order during the two contraction periods both with and without intact blood flow. Also the increase in phosphorylase a activity (from approximately 30% to approximately 65%) was the same during the contraction periods. Glycogenolytic and glucolytic rates were however about 30% higher (P less than 0.05) during the second contraction compared with the first when circulation was occluded, but similar when the circulation was intact. During the 60 s rest period, the phosphocreatine (PCr) was maintained at a low level and inorganic phosphate (Pi) remained increased under occluded circulation while PCr was resynthesized in the rest period with intact circulation. We conclude that the increased glycogenolytic rate observed during the second contraction with occluded blood circulation was due to the high [Pi] in the muscle and that the increased glucolytic rate was caused by high [Pi] and low [PCr]. In the rest period with anoxia the glycogenolysis was completely inhibited and glucolysis was inhibited by 95% in spite of the changes in [PCr] and [Pi].

The regulation of glycogenolysis in human muscle during epinephrine infusion has been investigated. The content of cAMP in resting muscle was 2.7 +/- 0.7 (SD) mumol . kg dry muscle-1 and increased threefold during the first 5 min of infusion. Total glycogen phosphorylase and glycogen synthase activities were unchanged during the infusion. The proportion of phosphorylase in the a form in the basal state was estimated to be at least 22.5% and during infusion 80–90%. During infusion, synthase I activity decreased. The muscle glycogen content was 340 mmol . kg dry wt-1 and decreased during the first 2 min of infusion at a rate of 11.0 mmol glycosyl units . kg dry wt-1 . min-1. Prolonged infusion resulted in a much lower glycogenolytic rate, even though most of the phosphorylase was still in the a form. Accumulation of hexose monophosphates and lactate followed the changes in glycogen. It was concluded that despite the almost total transformation of phosphorylase to the a form, the in vivo activity was maintained at a low level. It is suggested that this may be due to a low concentration of inorganic phosphate at the active site of the enzyme.

Phosphorylase was determined in biopsy samples frozen immediately or after a delay of 10 s to 6 min. Muscle biopsies were performed at rest without and with propranolol, or adrenalin infusion and after electrical stimulation. The phosphorylase a fraction was 36% (28-44) in resting samples frozen immediately and 12% (12-13) after 10 s delay and remained at the same level when the freezing was further delayed (up to 6 min). It is suggested that an increase in [Ca2+] in the cytoplasm due to the insertion of the needle in muscle or cutting of tissue membranes may cause transformation of phosphorylase from b to a form, a transformation which is restored when Ca2+ is pumped back during the delay. Also the increased phosphorylase a fraction observed in biopsy samples obtained during adrenalin infusion reverted partially back when freezing was delayed for 10 s and 30 s, respectively. In muscle samples taken during contraction the mole fraction of phosphorylase a decreased from 53 to 12% when freezing was delayed for 10 s. The lowest value of the phosphorylase a mole fraction was observed in resting muscle after beta-blockade when the tissue samples were frozen 10 s after sampling and corresponded to 10% of the total phosphorylase. It is concluded that both muscle sampling and circulating adrenalin will increase phosphorylase a fraction in resting muscle and probably also augment the effect of adrenalin infusion.

To determine the effects of epinephrine (EPI) infusion on muscle glycogenolysis and force production, the quadriceps muscles of both legs in six subjects were intermittently stimulated for 30 min. Contractions lasted 1.6 s (20 Hz) and were separated by 1.6 s of rest. EPI was infused (approximately 0.14 micrograms.kg body wt-1.min-1) in one leg during the last 15 min and the vastus lateralis was biopsied at rest (control leg only) and after 15, 18 (EPI leg only), and 30 min of stimulation. EPI infusion doubled the mole fraction of phosphorylase a (22.5 ± 4.1 to 44.8 ± 9.0%) and glycogenolysis (2.16 ± 0.72 to 5.45 ± 0.81 mmol glucosyl U.kg dry muscle wt-1.min-1) during stimulation. Muscle glucose 6-phosphate increased from 3.04 ± 0.17 to 6.43 ± 0.20 mmol/kg dry muscle wt, and lactate increased from 25.8 ± 4.4 to 34.3 ± 4.6 mmol/kg after 3 min of EPI infusion. Isometric force production was unaltered by EPI infusion. These results demonstrate a strong glycogenolytic effect of EPI infusion during prolonged electrical stimulation and suggest that the extra pyruvate formed was converted mainly to lactate. Exclusive anaerobic metabolism of the extra substrate would provide only a 10% increase in total ATP production, possibly accounting for the lack of improvement in force production. We suggest that the decrease in force production during prolonged electrical stimulation is related to decreased excitation of the contractile mechanism rather than inhibition of cross-bridge turnover caused by a shortage of energy or accumulation of hyproducts.

An enzymatic method is described for the determination of fructose-1-phosphate photometrically with fructose-6-phosphate kinase. By using the reaction rate to calculate the absorbance at the end of the reaction, the precision of the method is improved and the time taken for one assay reduced from 2 to 3 hr to about 1 hr.

The concentrations of ATP, phosphocreatine (PCr), creatine, and lactate were determined in muscle biopsy samples frozen immediately or after a delay of 1–6 min. During the delay the samples were exposed to normal air or a gas mixture of 6.5% CO2-93.5% O2. The ATP content was unchanged, but PCr increased significantly from 72 mmol after rapid freezing to 85 mmol X kg dry muscle-1 during the 1st min in air. The lactate concentration increased (2.8 to 5.2 mmol X kg-1). If muscles were made anoxic by circulatory occlusion for 4–6 min before sampling, no increase in PCr was observed. Direct homogenization of fresh tissue in perchloric acid gave the same ATP, PCr, and lactate contents as frozen samples. It is concluded that the ATP and PCr contents in muscle are unaffected by freezing but that the biopsy procedure activates the energy utilization processes resulting in PCr decrease. It is suggested that the muscle PCr content after a 1-min delay in tissue freezing corresponds to the level in resting fresh muscle.

Force and relaxation time were measured during intermittent electrical stimulation of the quadriceps muscle on 14 volunteers. Each stimulation had a duration of 1.6 s and the work to rest ratio was 1:1. Relaxation times increased during the first 20-30 contractions and then reached a plateau. The rate of increase in relaxation time during the first contractions as well as the plateau levels were found to correlate to maximal oxygen uptake capacity, predicted from submaximal cycle ergometer tests. Since slow-twitch fibres are known to produce work at a lower energy cost it is suggested that studies of relaxation time changes could provide functional estimates of fibre-type proportions in the quadriceps muscle.

At rest the cAMP concentration in (muscle samples of) the quadriceps femoris ranged from 1.55 to 3.00 mumol per kg dry muscle and in plasma from 15.3 to 32.3 nmol per 1. Blockade of the beta adrenoreceptors with propranolol resulted in a significant decrease in the concentration in muscle at rest, the magnitude of the fall being related to the initial level. Similarly in plasma there was a trend towards lower levels of cAMP in those with the highest pretreatment levels, but the overall change was not statistically significant. There was no relation between the concentrations in muscle and plasma, before or after beta-blockade. Maximum dynamic exercise for 4-8 min resulted in an approximate doubling in the cAMP concentration in both muscle and blood. The increase in plasma was closely related to that in muscle. Beta-blockade inhibited totally the rise in cAMP in muscle during exercise but was marginally less effective in preventing the increase in blood. No increase in plasma or muscle cAMP levels during 40-70 s isometric contraction were observed.