Human myocardial and skeletal muscle enzyme activities: creatine kinase and its isozyme MB as related to citrate synthase and muscle fibre types

Summary. Activities of myocardial and skeletal muscle total creatine kinase (CK) and its isozyme MB were related to the oxidative capacity [measured as the citrate synthase (CS) activity] and to the contractile characteristics (estimated as the percentage of type I muscle fibres). Skeletal muscle biopsies were obtained both from physically trained and untrained men and myocardial biopsies from patients subjected to open-heart surgery performed because of mitral or aortic valve disease. Enzyme activities were determined on freeze-dried muscle specimens. The CK-MB activity was about twice as high in trained skeletal muscle as in untrained ones reaching the myocardial level. The total CK activity was about three times higher in skeletal muscle than in myocardium; the myocardium, however, had CS activity 3–4 times larger than that of skeletal muscle. A close correlation was demonstrated between activities of CK-MB on one hand and CS (r= 0·76) or percentage type I fibres (r= 0·83) on the other hand suggesting a connection between CK-MB activity and the oxidative capacity of the cell. This was in contrast to total CK where different regressions were obtained when comparing the myocardium and the skeletal muscle of trained or untrained men. In conclusion, CK-MB activity in trained skeletal muscle in athletes were similar to that in myocardium. CK-MB was related to the oxidative capacity and formation of cellular energy in skeletal and heart muscle.     

Skeletal muscle fibre types and sizes in anorexia nervosa patients

Summary. Fibre type composition and fibre areas in skeletal muscle of anorexia patients were studied on biopsies from the m. quadriceps femoris in five male and five females, whose body weight was 2–3-5 SDs less than expected from the normal weight/height relationship. In two of the males, the muscle studies were also made after rehabilitation. A higher than normal percentage of type I fibres was found in the patients (male, 62 ±12, female, 69 ±7) whereas the percentage of type IIA fibres did not differ from normal individuals (male, 38 ±12, female 24 ±15). Of note was the observation that no type IIB fibres were found and some patients had an increased occurrence of the normally rare type IIC fibres. All muscle fibres were markedly atrophied with the mean cross-sectional area of type IIA fibres being significantly smaller (male, 26-1 ±3–7, female, 21-2 ±10-3, fi.m²×10^-2) than the mean area of type I fibres (male, 34-1 ±4–7, female, 35-3±7-4, (j.m²× 10^-2). In the two males studied after rehabilitation (body weight increased 12 and 19 kg), mean fibre area had increased by 40%. Our results suggested that a predominant part of the reduction in body weight and lean body mass, seen in adolescent children suffering from anorexia nervosa, could be accounted for by a loss of skeletal muscle mass. In the six subjects where marker enzymes of glycolytic (TPDH, LDH) and mitochondrial pathways (CS, HAD) were assayed, the former were 50% and the latter 10–20% below sedentary controls. Maximal oxygen uptake was only 35 (males) and 29 (females) ml/kg min^-1; this contrasted with the physical activity pattern of these patients, yet was in line with their small muscle mass with its low oxidative potential.     

High blood pressure and muscle morphology/metabolism – causal relationship or only associated factors?

As muscle tissue constitutes a main target organ for glucose metabolism and is responsible for the development of insulin resistance, it seems plausible to elucidate the relationship between blood pressure and muscle morphology and metabolism. The association between blood pressure and capillarization/morphology of the vastus lateralis muscle and metabolic variables was evaluated in 24 perimenopausal obese women [body mass index (BMI) 34·9 ± 1·1; waist–hip ratio (WHR) 0·90 ± 0·02]. The muscle enzyme activity of lipoprotein lipase (LPL), citrate synthase and glycogen synthase was determined. There was a significant negative correlation between the percentage of type I fibres and relative fibre area of type I on the one hand and systolic and diastolic blood pressure on the other. There was a negative correlation between the capillary density (i.e. number of capillaries/muscle fibre) and a positive correlation between the diffusion distance (fibre area supplied by one capillary) and diastolic blood pressure. The activities of LPL and citrate synthase were positively correlated with the percentage of type I and negatively correlated with the percentage of type II muscle fibres. The activity of LPL was also negatively correlated with plasma glucose and the insulin/C-peptide ratio. The insulin/C-peptide ratio was positively correlated with the percentage of type II muscle fibres. In stepwise multiple regression analyses, 20–30% of the variation in systolic and diastolic blood pressure could be explained by the variables of muscle fibre distribution. Excluding muscle morphological variables from the regression model, the insulin/C-peptide ratio accounted for 13% of the variation in systolic and diastolic blood pressure. The results of the study show the close association between muscle morphology and blood pressure. It remains to be elucidated whether this association indicates a causal relationship.     

Elevated endothelial-cell-stimulating angiogenic factor activity in rodent glycolytic skeletal muscles.

1. Capillary density is greater in skeletal muscles comprised of predominantly oxidative (type I) fibres than in those comprised of mainly glycolytic (type II) fibres. In order to investigate further the angiogenic mechanisms involved in muscle capillarization, endothelial-cell-stimulating angiogenic factor activities in various rodent skeletal muscles were compared. 2. Eleven untrained adult male Wistar rats were killed and the predominantly oxidative (type I) muscle,s soleus and heart, the predominantly glycolytic (type II) muscle, extensor digitorum longus, and the mixed-fibre muscle, gastrocnemius, were removed. Each sample was separately homogenized and centrifuged and the supernatants were diafiltered to isolate the low-molecular-mass fraction containing endothelial-cell-stimulating angiogenic activity. This was assayed for its ability to activate latent collagenase and was expressed as units, where 1 unit represents the percentage activation of the enzyme h-1 (mg of protein in the supernatant)-1. 3. The results (medians and ranges) demonstrated significantly greater endothelial-cell-stimulating angiogenic factor activity in extensor digitorum longus muscle (2.14 units, 0.62-2.87 units, n = 13) than in soleus (0.82 units, 0.59-1.79 units, n = 15), gastrocnemius (0.34 units, 0.28-0.40 units, n = 4) or heart (0.43 units, 0.16-0.52 units, n = 11) (P less than 0.01 for each) muscle. 4. These findings suggest that endothelial-cell-stimulating angiogenic activity in muscle is either inversely or not related to the local capillary density, which may be at or near a maximum in physiologically contracting, predominantly oxidative muscles.     

A simple and rapid method for the determination of the concentrations of magnesium, sodium, potassium and sodium, potassium pumps in human skeletal muscle

1. For the diagnosis of electrolyte disorders, data on skeletal muscle composition are often valuable, but rarely available. We have therefore developed a simple and rapid needle biopsy procedure for the determination of the concentrations of K+, Na+, Mg2+ and Na+, K+-pumps in muscle. 2. Using a Bergstr?m needle, biopsies weighing around 25 mg were taken from the vastus lateralis muscle of 18 normal subjects (aged 44-86 years) and extracted with trichloroacetic acid (TCA). The concentrations of K+, Na+ and Mg2+ were 90.7 +/- 1.8, 31.9 +/- 1.6 and 9.5 +/- 0.2 mumol/g wet wt., respectively (means +/- SE). 3. The TCA extraction gave the same values as digestion with 65% HNO3 or 35% H2O2, could be used over the weight range 10-55 mg and showed a Mg2+ recovery of 101.7%. 4. The concentration of Na+, K+-pumps was quantified as the total capacity for [3H]ouabain binding. In vastus lateralis biopsies obtained from six normal subjects the mean value was 258 +/- 16 pmol/g wet wt. 5. Comparison of the concentrations of K+, Mg2+ and [3H]ouabain-binding sites in samples obtained post mortem showed modest variation among different muscles with varying fibre composition. 6. Measurements of the concentrations of K+, Na+, Mg2+ and Na+, K+-pumps in duplicate biopsies of the vastus lateralis yield values which seen representative for the total pool of skeletal muscle fibres and can be performed within a few hours.(ABSTRACT TRUNCATED AT 250 WORDS)     

Muscle Fibre Types,Ubiquinone Content and Exercise Capacity in Hypertension and Effort Angina

The composition of skeletal muscle fibre expressed as a percentage of slow twitch (ST), type I or “red” and fast twitch (FT), type II or “white” were determined in patients with hypertension (HT) or with severe ischaemic heart disease (IHD) and compared to age matched controls. Similarly, exercise capacity expressed as the cycle intensity eliciting a blood lactate concentration corresponding to 2.0 mmol × 1–¹ were compared with healthy controls. Both patient groups had a higher percentage of FT fibres with relatively lower exercise capacities than their controls. The exercise capacities were reduced even when the relationship of decreased capacity with the percentage of increased FT was considered. There was an increase IHD but not in HT in patients with fibre subgroup FTc, which most probably reflected fibre trauma. Both patient groups were low in the skeletal muscle mitochondrial electron carrier and unspecific antioxidant ubiquinone, coenzyme Q₁₀ or CoQ₁₀. Patients with IHD but not HT showed, however, a faster fall in the ratio CoQ₁₀ over ST% the higher the percentage value of ST. The ratio reflects the antioxidant activity related to CoQ₁₀ in the fibre hosting most of the oxidative metabolism. A low ratio indicates a risk of metabolic lesion and cell trauma. This could explain fibre plasticity and offer an alternative cause to heredity in elucidating in deviating muscle fibre composition in patients with HT and IHD.     

Increased acylphosphatase levels in erythrocytes from hyperthyroid patients

Acylphosphatase activity and content were measured in erythrocytes from hyperthyroid patients and healthy controls. In addition, the soluble enzymes glucose-6-phosphate dehydrogenase, hexokinase, and the membrane bound (Na+ + K+)-ATPase and Ca2+-ATPase were assayed. Our results confirmed previous studies indicating a decrease of (Na+ + K+)-ATPase and an increase of Ca2+-ATPase activity in hyperthyroid erythrocytes. While glucose-6-phosphate dehydrogenase was not significantly changed, hexokinase and acylphosphatase activities were significantly higher in the hyperthyroid group. Both activities and content of acylphosphatase returned to normal levels in erythrocytes from treated patients, when they were euthyroid. These findings suggest that an excess of thyroid hormones may stimulate acylphosphatase biosynthesis in erythroid cells and indicate a potential clinical usefulness of this enzyme in hyperthyroidism.     

Determinants of insulin-stimulated skeletal muscle glycogen metabolism in man

Abstract. To examine factors which influence skeletal muscle glycogen synthesis in man, we related insulin sensitivity measured by euglycaemic insulin clamp in 43 healthy males to muscle glycogen synthase (GS) activity, GS protein content (Western blot), glycogen concentrations and fibre composition. Insulin increased muscle glycogen content (P<0.05) and the change in glycogen content correlated with the GS protein content (r=0.90, P=0.01). GS protein concentration correlated inversely with age (r=-0.69, P=0.04). Non-oxidative glucose disposal was inversely related to per cent type 2B fibres (r=-0.52, P< 005). The influence of age on these relationships was separately studied in young (n=12, age=26 ± 2 years) and elderly (n=15, age = 56 ± 2 years) males. Insulin increased GS activity significantly only in young subjects (from 17.8 ± 30 to 25.3 ± 3.2 nmol mg protein ' min^-1; P=0.015). GS activity and non-oxidative glucose disposal correlated in young (r=0.69, P=001) but not in the elderly (r=0.064, P = 0.82) males, and this relationship was not influenced by the degree of obesity. In conclusion, muscle fibre type and GS activity are both determinants of muscle glycogen metabolism in healthy, normoglycae-mic males. The close relationship between non-oxidative glucose metabolism and GS activity in young males is altered in ageing.     

Glycogen Phosphorylase Activity in Biopsy Samples and Single Muscle Fibres of Musculus Quadriceps Femoris of Man at Rest

Harris, R. C, Essén, B. & Hultman, E. Glycogen Phosphorylase Activity in Biopsy Samples and Single Muscle Fibres of Musculus Quadriceps Femoris of Man at Rest. Scand. J. clin. Lab. Invest. 36, 521–526, 1976.

Glycogen phosphorylase activity in biopsy samples of the quadriceps muscle of man taken at rest was measured in the direction of glycogen breakdown. The conditions of assay used were pH 6.8 and 35 d`C. Mean phosphorylase activity per kg fresh muscle in 8 male volunteers was: phosphorylase a - 259 U, and total phosphorylase - 627 U, where 1U is the production of 1 μmol glucose-1-phosphate/s under the conditions of assay. The mean value of total activity, transposed to the in vivo condition, is sufficient to support a maximum rate of glycogen degradation calculated as glucosyl units utilized per kg fresh muscle, of 627 μmol/s. This is approximately the rate at which glycolysis occurs during a maximum voluntary isometric contraction. The mean ratio of phosphorylase a activity to total activity at rest was 0.40. Estimates of the mean total phosphorylase activity in type I (‘slow’) muscle fibres isolated from the quadriceps of 9 volunteers ranged from 210–385 U/kg fresh muscle, and in type II (‘fast’) muscle fibres from 493–934 U/kg fresh muscle. The average ratio of activity in type II fibres compared with that in type I fibres was 2.5.     

ATP and IMP in single human muscle fibres after high intensity exercise

Summary. Within a muscle there is large variation in the activity of various enzymes among single fibres. It is reasonable, therefore, to expect a corresponding variation in their metabolic response to exercise. This was examined by obtaining muscle biopsies from five men at rest and after intense short-term exercise consisting of three bouts of 30 knee extensions each and intervened by 60 s rest. Freeze-dried dissected single fibres identified as type 1 or type 2 were analysed for ATP and IMP contents by liquid chromatography. Rest. Average ATP tended to be higher in type 2 than in type 1 fibres. The ATP range was 14–30 and 14–32 mmol × kg^-1 dry muscle (dm) in type 1 and 2 fibres, respectively. IMP was less than 1 mmol × kg^-1 dm in most fibres and similar in types 1 and 2. Exercise. Muscle force decreased 70% during exercise. The average decrease in ATP content was significant for both fibre types with somewhat larger response for type 2 (20%) than type 1 (10%) fibres. The ATP range was 10–28 and 10–30 mmol × kg^-1 dm in type 1 and 2 fibres, respectively. Average IMP content increased substantially in both fibre types, more so for type 2, and the range for individual fibres was 0–13 (type 1) and 0–21 (type 2) mmol × kg^-1 dm. Conclusion. After exhaustive short-term exercise, a large variation in ATP and IMP contents was evident among single type 1 and type 2 fibres. None of the fibres, however, showed an ATP content lower than 10 mmol × kg^-1 dm. It is suggested that the muscle force loss, demonstrated in the present study, is not attributed to a lowered ATP content per se.     

Proteasome proteolytic activity in skeletal muscle is increased in patients with sepsis

Patients with sepsis in the ICU (intensive care unit) are characterized by skeletal muscle wasting. This leads to muscle dysfunction that also influences the respiratory capacity, resulting in prolonged mechanical ventilation. Catabolic conditions are associated with a general activation of the ubiquitin-proteasome pathway in skeletal muscle. The aim of the present study was to measure the proteasome proteolytic activity in both respiratory and leg muscles from ICU patients with sepsis and, in addition, to assess the variation of proteasome activity between individuals and between duplicate leg muscle biopsy specimens. When compared with a control group (n=10), patients with sepsis (n=10) had a 30% (P<0.05) and 45% (P<0.05) higher proteasome activity in the respiratory and leg muscles respectively. In a second experiment, ICU patients with sepsis (n=17) had a 55% (P<0.01) higher proteasome activity in the leg muscle compared with a control group (n=10). The inter-individual scatter of proteasome activity was larger between the patients with sepsis than the controls. We also observed a substantial intra-individual difference in activity between duplicate biopsies in several of the subjects. In conclusion, the proteolytic activity of the proteasome was higher in skeletal muscle from patients with sepsis and multiple organ failure compared with healthy controls. It was shown for the first time that respiratory and leg muscles were affected similarly. Furthermore, the variation in proteasome activity between individuals was more pronounced in the ICU patients for both muscle types, whereas the intra-individual variation between biopsies was similar for ICU patients and controls.     

Activities of key enzymes in the energy metabolism of human myocardial and skeletal muscle

Summary. Activities of total creatine kinase (CK), its isoenzyme MB (CK-MB), total lactate dehydrogenase (LD) and its isoenzyme LD₁, phosphofructokinase (PFK), asparate aminotransferase (ASAT) and citrate synthase (CS) were determined in skeletal muscle biopsies obtained from physically trained and untrained men and in myocardial biopsies from patients subjected to open heart surgery because of valve disease. The LD₁, ASAT and CS activities were higher in trained than in untrained skeletal muscle and still higher in heart muscle than in either trained or untrained skeletal muscle. The CK-MB activity was higher in trained than untrained skeletal muscle and the myocardial CK-MB activity was similar to that in trained skeletal muscle. Total CK activity was slightly lower in trained than in untrained skeletal muscle and the myocardial CK activity was approximately one third of the skeletal muscle CK. Both the PFK and the total LD activity was of similar magnitude in the different muscle types. In conclusion, as estimated by enzyme activities, the oxidative capacity is 2–3 times larger in myocardial than in skeletal muscle, while the glycolytic capacity as estimated by PFK appears to be the same.     

Insulin resistance is associated with reduced fasting and insulin-stimulated glycogen synthase phosphatase activity in human skeletal muscle.

Insulin-stimulated glycogen synthase activity in human skeletal muscle correlates with insulin-mediated glucose disposal rate (M) and is reduced in insulin-resistant subjects. We have previously reported reduced insulin-stimulated glycogen synthase activity associated with reduced fasting glycogen synthase phosphatase activity in skeletal muscle of insulin-resistant Pima Indians. In this study we investigated the time course for insulin stimulation of glycogen synthase and synthase phosphatase during a 2-h high-dose insulin infusion (600 mU/min per m2) in six insulin-sensitive caucasians (group S) and in five insulin-resistant Pima Indians (group R). Percutaneous muscle biopsies were obtained from the quadriceps femoris muscle after insulin infusion for 0, 10, 20, 40, and 120 min. In group S, insulin-stimulated glycogen synthase activity increased with time and was significantly higher than in group R. In group S, synthase phosphatase activity increased significantly by 25% at 10 min and then decreased gradually. No significant change in synthase phosphatase was seen in group R and activity was lower than group S at 0 to 20 min. These data suggest that a low basal synthase phosphatase activity and a defect in its response to insulin explain, at least in part, reduced insulin stimulation of skeletal muscle glycogen synthase associated with insulin resistance.     

Muscle adaptations and glucose control after physical training in insulin-dependent diabetes mellitus

Summary. Six men and three women with insulin-dependent diabetes (without complications) participated in physical training three times a week for 20 weeks. Physical training did not change the concentration of fasting blood-glucose, glucose excretion in urine or glucosylated haemoglobin (Hb_A1). However, the glucose disposal rate during euglycaemic clamp increased after training. In two patients a minor reduction of insulin dosage was necessary to alleviate slight hypoglycaemic episodes. The training resulted in significant increases in quadriceps isometric and dynamic strength and endurance. Maximal oxygen uptake increased by 8%, the activity of glycolytic enzymes in vastus lateralis muscle by 47% for hexokinase, and 30% for tri-osephosphate dehydrogenase and 25% for lactic dehydrogenase, the activity of oxidative enzymes by 42% for citrate synthase and 46% for 3-hydroxy-acyl-CoA-dehydrogenase. The glycogen concentration in the vastus lateralis muscle did not change significantly. Lipoprotein lipase activity did not change in muscle, nor in adipose tissue. The mean muscle fibre area increased by 25% and the area of FTa fibres by 30%. The new formation of capillaries around different muscle fibres was significant for FTb fibres (26%). The proliferation of capillaries, however, appeared to be insufficient to cope with the increased area of muscle fibres. As a result, the mean area of muscle fibre supplied by one capillary (a measure of diffusion distance) significantly increased after training for FTa fibres. It is concluded that with the exception of deficient proliferation of capillaries, patients with insulin-dependent diabetes mellitus show a normal central and peripheral adaptation to physical training. Physical training does not apparently improve blood glucose control in most cases, despite an increased insulin sensitivity.     

Skeletal muscle morphology and exercise response in congenital generalized lipodystrophy

OBJECTIVE: Congenital generalized lipodystrophy (CGL) is an autosomal recessive genetic disorder characterized by almost complete absence of adipose tissue, muscular appearance, and severe insulin resistance since birth. We investigated whether insulin resistance in CGL patients is associated with abnormal muscle morphology and whether increased muscularity imparts increased muscle strength and exercise capacity RESEARCH DESIGN AND METHODS: We obtained quadriceps muscle biopsies to study muscle fiber types and capillary density in three African-American women (aged 17-20 years) with CGL. We also assessed quadriceps muscle strength, muscle metabolism, and maximal O2 consumption in the patients. RESULTS: Quadriceps muscle biopsies revealed a markedly higher percentage of type II (fast-twitch glycolytic) muscle fibers in patients with CGL versus sedentary young women (75-78 vs. 47-57%, respectively). The capillary-to-fiber ratio (2.7-3.0), however, was normal. Cross-sectional areas of type I (slow-twitch oxidative) (1,262-2,685 microm2) and type II (2,304-3,594 microm2) fibers were far below the normal values (3,811-4,310 and 3,115-4,193 microm2, respectively), suggesting muscle hyperplasia but not hypertrophy The quadriceps muscle strength, as measured by Cybex, was below average; the maximal O2 consumption (23-32 ml x kg(-1) x min(-1)) was also below average. 31P nuclear magnetic resonance spectroscopy of the forearm muscles revealed normal pH and metabolic responses to static and dynamic exercises. CONCLUSIONS: We conclude that insulin resistance in patients with CGL is associated with an increased proportion of type II muscle fibers but not reduced capillary density. Increased muscularity in CGL is due to muscle hyperplasia and is not associated with increased muscle strength.     

Serum carnosinase activities in patients with alcoholic chronic skeletal muscle myopathy

1. Serum carnosinase activity was assayed in a group of alcoholic patients with and without histologically proven atrophy of type II skeletal muscle fibres, and in control subjects. No significant activity was detected in muscle biopsy samples or washed erythrocytes. 2. Serum carnosinase activity was significantly lower in chronic alcoholic patients compared with a group of age-matched controls. Alcoholics with abnormal muscle biopsies had significantly lower enzyme activities than either those patients with normal muscle biopsies or the controls. Serum enzyme activities in patients with normal muscle biopsies were not significantly different from controls. 3. Serum carnosinase activity was inversely correlated with the degree of muscle atrophy as measured by the type II fibre atrophy factor. There was a positive correlation between the enzyme activity and skeletal muscle mass as reflected by the creatinine-height index. Furthermore, the enzyme activity significantly increased, with resolution or improvement in the myopathy, in patients who abstained from alcohol. 4. Kinetic studies showed that the reduced carnosinase activity was due mainly to a decrease in the apparent Vmax. The apparent Km was significantly higher in the myopathic compared with non-myopathic alcoholics. Mixing serum from controls and patients with myopathy gave the expected values, indicating the absence of a serum enzyme inhibitory factor. Acute alcohol loading had no effect on the serum carnosinase activity. 5. The decrease in serum carnosinase activity in alcoholics was not related to the severity of their liver disease. Assays of serum carnosinase in chronic alcoholics, can thus be used as a marker of their associated myopathy.     

Taurine content and distribution in equine skeletal muscle.

Taurine (TAU) is found in large but variable amounts in the skeletal muscles of many species. It has been reported that slow twitch muscles in the rat exhibit higher TAU levels than fast twitch muscles. Variation in muscle taurine content may be attributable to differences in the fibre type composition of different muscles. TAU content (mmol kg-1 dry muscle) and percentage type-1, type-2A, and type-2B fibre section area (f.s.a.) were measured in muscle samples taken from up to six sites in the middle gluteal muscle of four horses and one pony at post mortem and in biopsy samples taken from twenty Thoroughbred horses in race training. TAU was positively correlated to type-1 f.s.a. (r = 0.94, p < 0.001) in both post mortem samples and biopsies from horses in race-training. Multiple linear regression analysis was used to estimate the TAU content of individual fibre types when present at 100%. TAU is almost exclusively localized in type-1 fibres. The TAU content of type-1 and type-2A fibres was estimated to be 45.4 mmol kg-1 d.m. and 4.5 mmol kg-1 d.m. respectively in the post mortem horses, and 32.4 mmol kg-1 d.m. and 7.9 mmol kg-1 d.m. respectively in the horses in training. TAU was estimated to be absent from type-2B fibres in both horse groups.     

Maximum rate of oxygen consumption related to succinate dehydrogenase activity in skeletal muscle fibres of chronic heart failure patients and controls

Previous studies indicate that the low maximum rate of oxygen consumption (VO2max) of chronic heart failure (CHF) patients is not because of impaired pump function of the heart. We hypothesize that VO2 during maximum exercise is determined by the total oxidative capacity of skeletal muscle. VO2max of six controls and 14 CHF patients, New York Heart Association class I-III, was determined using an incremental bicycle ergometer test. Cryostat sections of a biopsy from the quadriceps femoris muscle were incubated for succinate dehydrogenase (SDH) using quantitative histochemistry. VO2max (range: 29 ml O2 kg muscle(-1) min(-1) in a class III patient to 118 ml O2 kg muscle(-1) min(-1) in a control subject) correlates with the mean SDH activity of skeletal muscle fibres (r=0.79 or r=0.81, including or excluding oxygen uptake at rest, respectively; P<0.001). The relationship between VO2max and SDH activity is similar to that determined previously using isolated single muscle fibres and myocardial trabeculae under hyperoxic conditions. From the product of SDH activity and the cross-sectional area of the fibre (i.e. spatially integrated SDH activity), it is possible to calculate the maximum oxygen uptake rate per unit muscle fibre length. This uptake rate is linearly related to the number of capillaries per fibre (r=0.76, P<0.001) in all subjects, suggesting that oxidative capacity of skeletal muscle fibres in CHF patients decreases in proportion to the oxygen supply capacity of the microcirculation.     

Insulin treatment increases skeletal muscle fibre area in patients with diabetes mellitus type 2

The effects of insulin treatment on skeletal muscle characteristics were studied in 18 patients (62 ± 11 years) with poorly controlled diabetes mellitus type 2 (mean duration 7·5 ± 6 years). Skeletal muscle biopsy samples were taken from the lateral portion of the quadriceps muscle before and after a period of insulin treatment of 40 ± 14 days. Enzyme activities (phosphofructokinase, 3‐hydroxyacyl‐CoA dehydrogenase, citrate synthase, lactate dehydrogenase and creatine kinase) and myoglobin content were assessed. In a subgroup of 11 patients (60 ± 11 years), skeletal muscle fibre type composition (type I, IIA, IIB and IIC) and fibre type cross‐sectional area were also analysed. Following insulin treatment there were 32 and 38% increases, respectively, in the cross‐sectional areas of type IIA and IIB fast‐twitch fibres (P<0·02). The fibre type distribution did not change. The myoglobin content in muscle decreased by 20% (P<0·01). Of the enzymes tested, the 3‐hydroxyacyl‐CoA dehydrogenase activity decreased by 10% (P<0·04). Serum glucose, HbA1_C and serum triglyceride levels decreased (P<0·001) and body weight and arm muscle circumference increased (P<0·02). In conclusion, insulin treatment of patients with poorly controlled non‐insulin‐dependent diabetes mellitus increased the fast‐twitch fibre area, reduced myoglobin levels and decreased muscle enzyme activity related to fatty acid oxidation.     

Variability in muscle fibre areas in whole human quadriceps muscle: how to reduce sampling errors in biopsy techniques

Summary. A single biopsy is a poor estimator of the muscle fibre cross-sectional area (CSA) for a whole human muscle because of the large variability in the fibre area within a muscle. To determine how the sampling errors in biopsy techniques can be reduced, data on the CSA of type 1 and type 2 fibres obtained from cross-sections of whole vastus lateralis muscle of young men, have been analysed statistically. To obtain a good estimate of the mean fibre CSA in a biopsy, measuring all fibres in that biopsy gives the best result. To obtain a good estimate of the mean fibre CSA for a whole muscle, the number of biopsies has a much greater influence on the sampling error than the number of fibres measured in each biopsy, but the number of biopsies needed to obtain a given sampling error can vary by a factor of two. If the fibre CSA in three or more biopsies is measured, it is sufficient to measure only 25 fibres in each biopsy. If less than three biopsies are taken, there is no worthwhile reduction in sampling error when more than 100 fibres are measured. To determine the mean fibre CSA for a whole group of individuals, our preference is to maximize the number of individuals, and only take single biopsies. In conclusion, to determine the mean fibre CSA for this particular muscle with a certain precision, we suggest analysis of three biopsies, taken from different depths of the muscle, and measurement of 25 fibres in each biopsy.