Enzyme levels in pools of microdissected human muscle fibres of identified type: Adaptive response to exercise

Enzyme activities were determined in pools of type I (slow twitch) and IIA and II B (fast twitch) fibres of the thigh muscle from individuals engaged to a high degree in physical training of an endurance character and from non-endurance-trained controls. The endurance-trained (ET) group had significantly higher activity levels of the mitochondrial enzymes citrate synthase, malate dehydrogenase, and 3-OH-acylCoA dehydrogenase both in type I (2.1×, 1.7×, 1.4×) and in type IIA (2.3×, 1.8×, 1.4×) and IIB fibres (2.0×, 1.5 ×, 1.5×) than the non-endurance-trained (NET) group. Of the glycolytic enzymes, phosphofructokinase (PFK) in type I fibres was significantly higher (I.8×) in the ET than in the NET group whereas glyceraldehydephosphate dehydrogenase (GAPDH) in type I fibres was similar in the two groups. In type II fibres both PFK and GAPDH levels tended to be higher in the ET group. Lactate dehydrogenase (LDH) of both fibre types were not different in the two groups. Type 1 fibres differed significantly from type II fibres for all the six enzymes measured in both groups. However, no significant difference between fibres of types IIA and IIB was found. The results indicate that fibres of types I, IIA and IIB in human skeletal muscle all possess great adaptability with regard to their oxidative capacity. Furthermore, the data suggest that extensive endurance training may enhance the glycolytic capacity in both type I and type II fibres although the glycolytic capacity of the muscle as a whole generally is low in endurance trained subjects owing to a predominance of type I fibres. It is concluded that further studies are needed to determine whether there is a metabolic distinction between fibres of types IIA and IIB.     

Metabolic characteristics of fibre types in human skeletal muscle.

Muscle biopsy samples were obtained from healthy subjects in order to evaluate quantitative differences in single fibres of substrate (glycogen and triglyceride) and ion concentrations (Na+ and K+) as well as enzyme activity levels (succinate-dehydrogenase, SDH; phosphofructokinase, PFK; 3-hydroxyacyl-CoA-dehydrogenase, HAD; myosin ATPase) between human skeletal muscle fibre types. After freeze drying of the muscle specimen fragments of single fibres were dissected out and stained for myofibrillar-ATPase with preincubations at pH's of 10.3, 4.6, 4.35. Type I ("red") and II A,B, and C ("white") fibres could then be identified. Glycogen content was the same in different fibres, whereas triglyceride content was highest in Type I fibres (2-3 X Type II). No significant differences were observed for Na+ and K+ between fibre types. The activity for the enzymes studied were quite different in the fibre types (SDH and HAD, Type I is approximately 1.5 X Type II; PFK Type I is approximately 0.5 X Type II, Myosin ATPase Type I is approxiamtely 0.4 X Type II). The subgroups of Type II fibres were distinguished by differences in both SDH and PFK activities (SDH, Type II C is greater than A is greater than B; PFK, Type II B is greater than A is approximately C). It is concluded that contractile and metabolic characteristics of human skeletal fibres are very similar to many other species. One difference, however, appears to be than no Type II fibres have an oxidative potential higher than Type I fibres.     

Different metabolic responses to exercise training programmes in single rat muscle fibres

Summary The aim of this report is to elucidate the effects of exercise training on metabolic properties of different muscle fibre types of the rat hindlimb. Single muscle fibres were dissected from soleus (SOL) or extensor digitorum longus (EDL) muscles of Wistar strain male rats trained on a treadmill for 16 weeks. Each fibre was typed histochemically (SO, slow-twitch oxidative; FOG, fast-twitch oxidative glycolytic; FG, fast-twitch glycolytic). Then glycolytic and oxidative enzymes (CK, LDH, PFK, PK, SDH, and MDH) activities were measured biochemically. Slow,-type fibres (SO) were hypertrophied following endurance training and fast-twitch fibres (FOG and FG) were hypertrophied following sprint training. In EDL muscles the distribution of the slow-type fibres was reduced following the sprint training. The activity of glycolytic enzymes increased significantly in the fast-type fibres (FOG and FG) following sprint training, while oxidative enzymes activities increased in both fast (FOG and FG) and slow (SO) muscle fibres following the endurance training. Neither glycolytic nor oxidative enzymes' activities always increased equally in all types of fibre following exercise training. Consequently, the metabolic profiles in each type of single muscle fibre were affected differently by different intensities of exercise training. These results suggest that the functional (enzymes activity) and structural (muscle fibre hypertrophy) changes of skeletal muscle fibre following exercise training appeared gradually, and would be controlled by different factors.     

Differences in ultrastructural and metabolic profiles within the same type of fibres in various muscles of young and adult rats

Single fibres from tibialis anterior, extensor digitorum longus, gastrocnemius and soleus muscles in young (4–week–old) and adult (35–week–old) Wistar male rats were classified into three types on the basis of their enzyme–histochemical features: slow–twitch oxidative (SO), fast–twitch oxidative and glycolytic (FOG) and fast–twitch glycolytic (FG) fibres. Ultrastructural (volume density of mitochondria: V_mt and Z line width) and metabolic (phosphofructokinase: PFK and succinate dehydrogenase: SDH activities) profiles were measured. PFK activity in all types of fibres¹ was higher in adult rats, and the difference between the two age–groups (adult/young) was largest between FG, FOG and SO fibres respectively. SDH activity and V_mt were lower in adult rats in a similar way in all fibres. A significant positive correlation was observed between the V_mt and SDH activity in both age–groups. This positive correlation was very specific in fast–twitch and slow–twitch fibres. Changes in the V_mt did not relate directly to the changes in fibre cross–sectional area. The overall pattern indicates that glycolytic capacity of fast–twitch fibres in flexor muscles (TA and EDL) is higher than in extensor muscles (GC and SOL), and that oxidative capacity of all types of fibre in extensor muscles is higher than in flexor muscles. These profiles were changed by growth, and may be related to the specific differences in pattern of activity of each skeletal muscle, and may reflect differences in the recruitment order of different muscles.     

Fibre type related changes in the metabolic profile and fibre diameter of human vastus medialis muscle after anterior cruciate ligament rupture

Vastus medialis muscles of patients with chronic anterior instability of the knee after anterior cruciate ligament rupture were analysed to investigate changes in defined muscle fibres of the diseased leg in comparison to the healthy leg of the same patient. Metabolic and morphological parameters were obtained by cytophotometrical measurements of the activities of succinate dehydrogenase (a marker of oxidative metabolism) and glycerol-3-phosphate dehydrogenase (a marker of glycolytic metabolism) of slow-oxidative (SO), fast-oxidative glycolytic (FOG) and fast-glycolytic (FG) fibre types in serial sections and by measuring the minimal fibre diameters of type I (slow) and type II (fast) fibres. We found decreased glycolytic activity and a shift to more oxidative metabolism in each fibre type suggesting diminished fast force and shift to endurance force development. The latter was interpreted as a sign of active compensation for the knee instability. Significantly decreased minimal fibre diameters to 85.9% in type I fibres, and to 88.7% in type II fibres of the diseased muscle were measured, indicating the fibre atrophy. Our findings suggest that the atrophied muscle fibres of the affected vastus medialis muscle adapt to the altered conditions by changing their metabolic profile. Muscle fibres of different types were found to be affected similarly.     

Enzyme levels of the NADH shuttle systems: measurements in isolated muscle fibres from humans of differing physical activity

The aim of the present study was to investigate enzyme levels of the malate-aspartate and alpha-glycerophosphate shuttles in type I (slow-twitch) and type II (fast-twitch) fibres of human skeletal muscle. The influence of endurance training on these levels was also elucidated. Biopsy specimens were obtained from the lateral part of the quadriceps femoris muscle of six untrained and six endurance-trained subjects. Type I vs. type II. In both groups the type I fibres exhibited higher levels of the TCA cycle marker enzyme citrate synthase (CS), as well as of the malate-aspartate shuttle enzymes (cytoplasmic and mitochondrial malate dehydrogenase (cMDH, mMDH), and aspartate aminotransferase (cASAT, mASAT]. A more pronounced difference between type I and type II fibres was noted for cMDH (58%) than for mMDH (16%), cASAT (20%), mASAT (18%) and CS (25%). In contrast to these enzymes, the levels of cytoplasmic glycerol-3-phosphate dehydrogenase (cGPDH), the enzyme representative of the alpha-glycerophosphate shuttle, were higher (25%) in the type II fibres. Endurance-trained vs. untrained. In the endurance-trained group, both fibre types were characterized by higher levels of CS (mean for both fibre types: 48%) as well as of mitochondrial malate-aspartate shuttle enzymes (mMDH: 47%, mASAT: 48%) than in the corresponding fibre types in the untrained group, while the differences in the levels of cytoplasmic malate-aspartate shuttle enzymes (cMDH: 13%, cASAT: 16%) were not statistically significant. Nor were the differences in cGPDH levels (8%) between the untrained and endurance-trained groups statistically significant. It is concluded that in human skeletal muscle, malate-aspartate shuttle enzymes are expressed to a higher degree in type I (slow) fibres than in type II (fast) fibres, with cMDH exhibiting the most marked difference. The single fibre analysis indicated that the muscle's activity level might exert a greater influence on the mitochondrial isoenzymes than on the cytoplasmic ones. In contrast to the malate-aspartate shuttle enzymes, the alpha-glycerophosphate shuttle is expressed to a higher degree in type II fibres and its capacity appears to not be influenced by endurance training. The present studies demanded considerable methodological investigations which also are presented in this paper.     

Metabolic Characteristics of Fibre Types in Human Skeletal Muscle

Muscle biopsy samples were obtained from healthy subjects in order to evaluate quantitative differences in single fibres of substrate (glycogen and triglyceride) and ion concentrations (Na⁺ and K⁺) as well as enzyme activity levels (succinate-dehydrogenase, SDH; phosphofructokinase, PFK; 3-hydroxyacyl-CoA-dehydrogenase, HAD; myosin ATPase) between human skeletal muscle fibre types. After freeze drying of the muscle specimen fragments of single fibres were dissected out and stained for myofibrillar-ATPase with preincubations at pH's of 10.3, 4.6, and 4.35. Type I (“red”) and II A, B, and C (“white”) fibres could then be identified. Glycogen content was the same in different fibres, whereas triglyceride content was highest in Type I fibres (2–3 × Type II). No significant differences were observed for Na⁺ and K⁺ between fibre types. The activity for the enzymes studied were quite different in the fibre types (SDH and HAD, Type I ? 1.5 × Type II; PFK Type I ? 0.5 × Type II; Myosin ATPase Type I ? 0.4 × Type II). The subgroups of Type II fibres were distinguished by differences in both SDH and PFK activities (SDH, Type II C > A > B; PFK, Type II B > A ? C). It is concluded that contractile and metabolic characteristics of human skeletal fibres are very similar to many other species. One difference, however, appears to be that no Type II fibres have an oxidative potential higher than Type I fibres.     

Enzyme activities in type I and II muscle fibres of human skeletal muscle in relation to age and torque development

The quadriceps muscles from 20- 30- and 70-year-old clinically healthy men and women were studied regarding maximal isometric and isokinetic muscle torque in Newton metres (Nm), morphology and enzyme activity. Biopsy specimens were taken from the vastus lateralis muscle and freeze-dried, and individual fibres were dissected out and identified as type I or type II. The activities of citrate synthase (CS), 3-OHacyl-coA dehydrogenase (HAD), lactate dehydrogenase (LDH), myokinase (MK) and creatine phosphokinase (CPK) were determined in pools of type I and type II fibres. In both age groups a higher oxidative (CS, HAD, 1.3-1.5 x) and a lower glycolytic (LDH, 0.7 x) capacity was found in type I than in type II fibres. The myokinase activity was higher in type II (2 x) than in type I, whereas CPK activity was similar. The young men showed higher CS activity in both type I and type II fibres (1.5 x) and higher CPK activity in type I fibres (1.4 x) than the young women. There were only minor changes in oxidative or glycolytic capacities in relation to age. Myokinase was the only enzyme that decreased markedly with age in both pools of fibre types. Type II fibre area and mean fibre area correlated significantly to muscle torque in both sexes. In men, myokinase activity in type II fibres was significantly correlated to type II fibre area and to maximal muscle torque.     

Determination of metabolic profiles on single muscle fibres of different types

Summary Single muscle fibres separated from extensor digitorum longus (EDL) as well as soleus (SOL) in the Wistar strain male rat in relaxing solution were typed histochemically, then glycolytic and oxidative enzyme activities were determined on the same fibres. Glycolytic enzyme lactate dehydrogenase (LDH), phosphofructokinase (PFK), pyruvate kinase (PK) and creatine kinase (CK) showed highest activities in fast-twitch glycolytic (FG), lower in fast-twitch oxidative glycolytic (FOG) and lowest in slow-twitch oxidative (SO) fibres. Also oxidative enzyme succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) showed highest activities in SO, lower in FOG and lowest in FG fibres. The activities of LDH, PFK, PK and CK in FOG fibres separated from EDL showed higher activity compared to those separated from SOL, whereas the opposite result was obtained for the activities of SDH and MDH. Enzyme activities in a single muscle fibre type were not distinguishable from those of another type, and the activity profiles overlapped over a considerable range. The correlations among the separate enzyme activities of CK, LDH and MDH obtained from the same single fibre overlapped over a considerable range.     

Coexistence of slow and fast isoforms of contractile and regulatory proteins in human skeletal muscle fibres induced by endurance raining

The distribution of fast and slow isoforms of troponin C, I, and T components and myosin heavy chains was investigated in histochemically typed myofibrillar ATPase intermediate (IM) fibres, that is, fibres that stain after both acid and alkaline pre-incubation in stainings for myofibrillar ATPase. In addition to the previously described IM fibres of types II C and I B, fibres that displayed staining characteristics between types II C and I B were observed and termed type II C–I B. The IM fibres constitute less than 1% of the fibres in normal human limb and abdominal muscles. The IM fibres studied here resulted from extensive endurance training of human triceps brachii muscle (n= 6) and were induced by conversion of a proportion (130) of type II fibres. The immunohistochemical stains of serial sections with antibodies to slow isoforms of troponin I, T, C and myosin heavy chain showed no staining of type II fibres but intense staining of types I and I B fibres, whereas type II C fibres stained with intermediate intensity. The antibodies to fast isoforms of the troponin components and myosin heavy chain did not give rise to staining of type I fibres but dark staining of type II fibres. Type I B fibres stained with intermediate intensity and type II C was either as dark as type II or slightly lighter. Type II C-I B fibres showed staining intensities intermediate between those observed for types I B and IIC in the immunohistochemical stains. It is therefore concluded that training-induced myofibrillar ATPase intermediate human skeletal muscle fibres are characterized by the coexistence of slow and fast isoforms of contractile and regulatory proteins. Changes in the distribution of fast and slow isoforms of several of the myofibrillar proteins appeared to be induced in a co-ordinated manner.     

Myopathy-dependent changes in activity of ATPase, SDH and GPDH and NOS expression in the different fibre types of hamster muscles

Proximal (vastus lateralis) and distal (gastrocnemius) muscles of 100-day-old normal and myopathic BIO TO-2 hamsters were analysed to study the effects of myopathy on the different muscle fibre types: SO (slow oxidative), FOG (fast oxidative glycolytic) and FG (fast glycolytic). Cytophotometric measurements of enzyme activities (myofibrillic adenosine triphosphatase, succinate dehydrogenase and glycerol-3-phosphate dehydrogenase), Western blot analysis of nitric oxide synthase (NOS) I, II, III isoforms and NOS II immunohistochemistry were performed. The following alterations were found in myopathic muscle fibres: all fibre types of both proximal and distal myopathic muscles showed decreased myofibrillic adenosine triphosphatase activity indicating depressed contractility. This was associated with depressed oxidative activity of the muscle fibres. A shift to more glycolytic metabolism was observed, mainly in FG fibres of proximal muscle. We found an increased NOS II expression in both myopathic muscle types investigated. It means that increased NO production inhibits force generation in myopathic muscle. NOS II immunoreactivity was found mainly in the cytoplasm of FG fibres. NOS I and NOS III expression was not significantly effected by this form of myopathy. Our findings demonstrate that muscle fibres of proximal and distal skeletal muscles of 100-day-old cardiomyopathic BIO TO-2 hamsters are altered with respect to contractility, metabolism and NOS II expression. FG fibres of the proximal muscle were effected most strongly.     

Quantitative measures of enzyme activities in type I and type II muscle fibres of man after training.

The effect of 7 to 8 weeks of physical training on oxidative and glycolytic enzyme activities in the 2 major fibre types of human quadriceps femoris muscle has been investigated. 2 groups of 4 and 5 subjects respectively were trained at the same total work-load on a bicycle ergometer 3 days per week using interval exercise with maximal intensity (I.T.) or continuous exercise with submaximal intensity (C.T.). Succcinate dehydrogenase (SDH) and phosphofructokinase (PFK) activities were determined on crude homogenates of muscle biopsy samples and on pools of type I and type II fibres dissected from freeze-dried samples taken before and after training. Crude homogenate SDH activity increased to the same extent in both groups, average increases were 27.5% (I.T.) and 22% (C.T.) respectively. Only type I-SDH increased in the C.T. group (p less than 0.01), the average increase being 32%. On the other hand only type II-SDH increased in the I.T. group (p less than 0.01), with an average increase of 49%. No changes in PFK activity could be detected. The results of the present study emphasize the great adaptability in oxidative potential of both the two major human skeletal muscle fibre types and further that this adaptation seems to be related to the pattern of fibre recruitment during exercise.     

Muscle adaptation to extreme endurance training in man.

To evaluate the effect of extreme endurance training on muscle fibre composition and activities of oxidative enzymes in different fibre types biopsies were taken from vastus lateralis, gastrocnemius and deltoideus of elite orienteers. Comparisons were made between the (trained) leg muscles and the (relatively untrained) arm muscles, and with leg muscles of 16--18 years old boys. The orienteers had the same percentage type I fibres and vastus lateralis and gastrocnemius as in deltoideus, but higher percentage type I fibres in vastus lateralis compared with the controls. The similarity between trained and untrained muscle in the orienteers suggests that training had not caused the high percentage type I fibres which rather might be the result of selection of individuals with the best prerequisites for high oxidative capacity. However, the distribution of type II subgroups in the leg muscles of the orienteers differed from both their own deltoideus and leg muscles of the controls, the relationship IIA/IIB being altered in favour of the more oxidative IIA. The leg muscles of the orienteers also showed an increased occurrence of the normally IIC fibre. These latter findings point at the possibility of a training induced alteration in the subgroup pattern. Unlike in the controls there was no significant difference in succinate dehydrogenase activity, measured in single fibres, between type I and II fibres in gastrocnemius of the orienteers. Thus, type II fibres have the ability metabolically to adapt to high oxidative demands. This might to some extent be mediated by a conversion from IIB to IIA form.     

Muscle Adaptation to Extreme Endurance Training in Man

To evaluate the effect of extreme endurance training on muscle fibre composition and activities of oxidative enzymes in different fibre types biopsies were taken from vastus lateralis, gastrocnemius and deltoideus of elite orienteers. Comparisons were made between the (trained) leg muscles and the (relatively untrained) arm muscles, and with leg muscles of 16–18 years old boys. The orienteers had the same percentage type I fibres in vastus lateralis and gastrocnemius as in deltoideus, but higher percentage type I fibres in vastus lateralis compared with the controls. The similarity between trained and untrained muscle in the orienteers suggests that training had not caused the high percentage type I fibres which rather might be the result of selection of individuals with the best prerequisites for high oxidative capacity. However, the distribution of type II subgroups in the leg muscles of the orienteers differed from both their own deltoideus and leg muscles of the controls, the relationship IIA/IIB being altered in favour of the more oxidative IIA. The leg muscles of the orienteers also showed an increased occurrence of the normally rare IIC fibre. These latter findings point at the possibility of a training induced alteration in the subgroup pattern. Unlike in the controls there was no significant difference in succinate dehydrogenase activity, measured in single fibres, between type I and II fibres in gastrocnemius of the orienteers. Thus, type II fibres have the ability metabolically to adapt to high oxidative demands. This might to some extent be mediated by a conversion from IIB to IIA form.     

Capillary supply and mitochondrial content of different skeletal muscle fiber types in untrained and endurance-trained men. A histochemical and ultrastructural study

Summary The number of capillaries per fiber, per mm², around each fiber type and relative to fiber area was determined in six untrained subjects (UT) and six elite cross-country skiers (ET). Average values for maximal oxygen uptake were 49.8 ml·kg^–1·min^–1 (UT) and 77.9 ml·kg^–1·min^–1 (ET). Type I fibers constituted 39.2% (UT) and 68.6% (ET), type II A fibers 39.6% (UT) and 19.2% (ET), while 12.8% (UT) and 6.6% (ET) of the fibers were type II B. The mean fiber area for the type II A fibers was significantly greater (p<0.01) than the areas for type I and II B in the untrained group.The average numbers of capillaries around each fiber type (CA) were 4.76-4.84-2.94 (UT) and 7.79-6.63-4.5 (ET) for type I, II A, and II B, respectively. There was a significant difference (p<0.01) in the CA values relative to fiber area for all fiber types in both groups, being highest for type I and lowest for type II B. The CA increased linearly with increasing size of the fibers for all fiber types in both groups.The mitochondrial content was determined semiquantitatively for each fiber type. The differences in capillary supply between the fiber types are accompanied by similar differences in mitochondrial content.The results indicate that endurance training increases the capillary supply of all fiber types in the human quadriceps muscle. The fact that light microscopical studies have given lower capillarization values than those obtained with the electron microscope is discussed.     

Differences of morphometrical parameters in hind limb muscle fibres between ovarectomized and sexually intact female dogs.

Slow and fast twitch fibres of the Mm. tibialis cranialis, semitendinosus and sartorius of seven sexually intact and seven ovarectomized female beagles were histochemically and morphometrically analysed. Along with type I and type IIA fibres, another main type II fibre (IIS), which seems to be peculiar to the dog, was found in the Mm. semitendinosus and tibialis cranialis. Type I fibers comprised 26% and type II fibres 74% of all recorded muscle fibres in the M. tibialis cranialis, 29% (type I) and 71% (type II) in the M. semitendinosus and 51% (type I) and 49% (type II) in the M. sartorius, respectively. The average single profile area and the corresponding mean diameter of fibre types I and II in the investigated hind limb muscles were generally larger in ovarectomized than in sexually intact animals. This was more evident in type II than in type I fibres. However only the type II fibres of the M. tibialis cranialis and sartorius exhibited a statistically significant increase in diameter (p < 0.01 and p < 0.05, respectively). Accordingly, the mean density (number of fibres/mm2) of both fibre types in the hind limb muscles of spayed dogs was generally reduced. Again, this reduction attained statistical relevance in the type I and II fibres of the tibialis cranialis. In addition, the fibre densities of type I in the semitendinosus and type II in the sartorius muscles were also significantly reduced in ovarectomized dogs. In conclusion, ovarectomized beagles showed a generally increased mean diameter of the investigated type I and II hind limb muscle fibres and a concomitant decreased average fibre density of the respective types when compared to sexually intact animals.     

Ultrastructural and metabolic characteristics of single muscle fibres belonging to the same type in various muscles in rats

Summary Single muscle fibres from soleus (SOL) as well as extensor digitorum longus (EDL) muscles from Wistar male rats in relaxing solution were divided into three types by their histochemical features — slow-twitch oxidative (SO), fast-twitch oxidative glycolytic (FOG), or fast-twitch glycolytic (FG) fibres. The relationship between ultrastructural profiles (mitochondrial volume, number, and Z-line width) and metabolic profiles (glycolytic and oxidative enzymes' activity) were analysed using the same types of fibres dissected from different SOL and EDL muscles using stereological and biochemical techniques. The Z-line width is specialized in different fibre types. Fast-twitch (FG and FOG) fibres have narrow Z-line width compared to slow-twitch (SO) fibre in SOL and EDL muscles. A significant difference was observed between SOL muscle SO and FOG fibres and EDL muscle SO and FOG fibres. All glycolytic (lactate dehydrogenase (LDH), phosphofructokinase (PFK), pyruvate kinase (PK) and creatine kinase (CK) activities in FOG fibres from EDL muscles were significantly higher (p<0.01) than those dissected from SOL muscles. The oxidative enzyme (succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) activity in SO and FOG fibres dissected from SOL muscle were significantly higher (p<0.01) than those dissected from EDL muscles. Mitochondrial volume and number in SO fibres dissected from SOL muscle were significantly higher (volume,p<0.01, number,p<0.01) than those dissected from EDL muscles. A significant difference was not observed in mitochondrial volume of FOG fibres between SOL and EDL muscles. Significant positive correlation was observed in FOG (p<0.05) and FG (p<0.01) fibres between mitochondrial volume and number dissected from EDL muscle.The results suggest that the same type of single muscle fibres in different muscles have different ultrastructural and metabolic profiles, and these profiles resembled those of the fibre types primarily constituting those muscles.     

Creatine kinase MB and citrate synthase in type I and type II muscle fibres in trained and untrained men

Summary Total creatine kinase (CK), creatine kinase MB (CK-MB) and citrate synthase (CS) were determined in isolated and pooled type I and type II skeletal muscle fibres. Determinations were made on biopsies from 3 sedentary men, 3 junior cyclists and 2 elite cyclists. CS and CK-MB activities were higher in the trained groups in both fibre types. The total CK activity was not related to training status, although it was lower in type I fibres than in type II fibres (p<0.05). The reverse relation was observed for CS and CK-MB activities (p<0.01). The ratio of type I/type II for CS was not related to training status, while the corresponding ratio for CK-MB increased with a greater degree of endurance training. For a given increase in CS activity, the increase in CK-MB activity was greater in type I fibres than in type II fibres (p<0.01). Thus, with endurance training there seems to be a specific adaptation for CK-MB, particularly in type I fibres.     

Ultrastructural and metabolic profiles on single muscle fibers of different types after hindlimb suspension in rats

The relationships between ultrastructural and metabolic profiles in different types of single muscle fiber after hindlimb suspension in rats were examined. Glycolytic (lactate dehydrogenase, LDH; phosphofructokinase, PFK) and oxidative (succinate dehydrogenase, SDH; malate dehydrogenase, MDH) enzyme activities in extensor digitorum longus (EDL) and soleus (SOL) muscles were measured. Relative mitochondrial and lipid droplet volumes were also measured in single muscle fiber of different types. Glycolytic enzyme activity in EDL muscle and oxidative enzyme activity in soleus muscle decreased following suspension for 2 weeks. LDH and PFK activities in fast-twitch (FG, fast-twitch glycolytic; FOG, fast-twitch oxidative glycolytic) fibers and oxidative enzymes in FOG and FG fibers decreased following suspension. Relative mitochondrial volume decreased significantly in all types (SO, slow-twitch oxidative; FOG, and FG) of fibers following suspension. The mitochondrial volume in SO fiber of the control group was significantly (p less than 0.01) higher than that of suspended group; however, SDH and MDH activities were not different between the control and suspended groups. The structural and metabolic changes following hindlimb suspension were influenced by different factors, respectively. Changes in ultrastructural and metabolic profiles in response to the hindlimb suspension differed according to the type of fibers.     

Species-specific effects of chronic nerve stimulation upon tibialis anterior muscle in mouse,rat, guinea pig,and rabbit

Tibialis anterior (TA) muscle of mouse, rat, guinea pig, and rabbit was indirectly stimulated for 10 h/day at 10 Hz up to 28 days. Changes in the activity levels of hexokinase (HK), phosphofructokinase (PFK) glyceraldehydephosphate dehydrogenase (GAPDH), lactate dehydrogenase (LDH), creatine kinase (CK), citrate synthase (CS), malate dehydrogenase (MDH), 3-hydroxyacyl-CoA dehydrogenase (HADH), and -hydroxybutyrate dehydrogenase (HBDH) were compared. Although the direction of changes in the enzyme activity pattern was in accordance with previous findings on rabbit TA, the magnitude of the responses varied markedly between themammals under study. Mouse TA was almost unaffected. A major effect of chronic stimulation in rat, guinea pig and rabbit was an increase in enzyme activities of aerobic-oxidative metabolism. According to intrinsic differences of the muscles under study, the increases varied among the species and appeared to be inversely related to the basal levels of these enzymes in the unstimulated muscles. Conversely, glycolytic enzyme activities (PFK, GAPDH, LDH) markedly decreased in rat, guinea pig, and rabbit, and were only slightly reduced in mouse. Changes in HK and HBDH activities displayed the largest variations in the induced change between species. These results indicate species-specific patterns of metabolic adaptation to increased contractile activity.