Fiber Type Changes Research Articles

Differential modulation of carbonic anhydrase (CA III) in slow- and fast-twitch skeletal muscles of rat following denervation and reinnervation

Carbonic anhydrase III (CA III) is influenced by neuronal factors in skeletal muscles of the rat. CA III protein and its mRNA levels were assessed in slow- and fast-twitch muscles after short-term denervation by ligature of the sciatic nerve and reinnervation following removal of the sheath tightly fixed around the nerve. Significant elevations in the CA III mRNA content of fast-twitch muscles were recorded after denervation, but they were cancelled following spontaneous muscle reinnervation. No such variations were observed in the slow-twitch soleus muscle. CA III specific activity or cytosolic CA III protein content increased in both types of muscles after denervation, while a decrease was solely observed in the soleus after reinnervation. These results suggest that neuronal mediators may be responsible for up and down variations in CA III gene expression and (or) mRNA stability in slow- and fast-twitch muscles exposed to identical stimuli. Variations of the mRNA and the protein probably reflect, in a time-related manner, the well-programmed changes in fiber type of the muscles in the context of the denervation-reinnervation model.

Rostrocaudal pattern of fiber-type changes in an overloaded rat ankle extensor

Our aim was to quantify the overload-induced hypertrophy and conversion of fiber types (type II to I) occurring in the medial head of the gastrocnemius muscle (MG). Overload of MG was induced by a bilateral tenotomy/retraction of synergists, followed by 12-18 wk of regular treadmill locomotion (2 h of walking/running per day on 3 of 4 days). We counted all type I fibers and determined type I and II mean fiber areas in eight equidistant sections taken along the length of control and overloaded MG. Increase in muscle weights (31%), as well as in total muscle cross-sectional areas (37%) and fiber areas (type I, 57%; type II, 34%), attested to a significant hypertrophic response in overloaded MG. An increase in type I fiber composition of MG from 7.0 to 11.5% occurred as a result of overload, with the greatest and only statistically significant changes (approximately 70-100%) being found in sections taken from the most rostral 45% of the muscle length. Results of analysis of sections taken from the largest muscle girth showed that it significantly underestimated the extent of fiber conversion that occurred throughout the muscle as a whole. These data obtained on the MG, which possesses a compartmentalization of fiber types, support the notion that all fiber types respond to this model with a similar degree of hypertrophy. Also, they emphasize the complex nature of the adaptive changes that occur in these types of muscles as a result of overload.

Thermal expansion characteristics of PEEK composites

The thermal expansion behaviour of several fibre-reinforced PEEK composites is assessed. It is shown that thermal expansion behaviour is consistent, and changes in a predictable manner with changes in fibre type. Using a composite manufactured such that no interfacial bonding took place, it is demonstrated that compressive forces caused by differential thermal contraction of fibre and matrix are sufficiently large to dominate behaviour in a direction parallel to the fibres. This suggests that PEEK composites should be resistant to changes in thermal expansion behaviour with repeated thermal cycling, and such resistance is demonstrated for AS4/PEEK (APC-2/AS4). It is shown that conventional models for predicting laminate response from unidirectional composite properties are valid for such materials, but it is also shown that the common analytical models for calculating transverse fibre behaviour from composite properties are inaccurate.

Effects of Propranolol on Premature Action Potentials in Canine Purkinje and Ventricular Muscle

We compared the effects of a low (0.09 microgram/ml) concentration of propranolol expected to produce only beta-adrenoceptor blockade and a high concentration (0.9 microgram/ml) expected to produce additional direct local anesthetic-like electrophysiological effects on basic and premature action potentials. Both isolated dog cardiac Purkinje and ventricular muscle fibers were examined using conventional microelectrode techniques. The low concentration of propranolol produced no significant electrophysiological change in either fiber type. The high concentration of propranolol shortened the action potential duration and refractoriness while decreasing the maximal upstroke velocity (Vmax) in both Purkinje and ventricular muscle fibers at a constant basic cycle length. In Purkinje fibers, the high concentration also slowed the kinetics of restitution of the action potential duration (tau c from 124.6 +/- 6.5 to 201.4 +/- 16.0 ms, p less than 0.01, n = 7), slowed the recovery kinetics of Vmax, and shifted the early portion of the normalized restitution curve toward longer action potential duration values in both fiber types. The range of premature action potential durations, defined as the difference between action potential durations during the first 100 ms of restitution, was decreased by the high concentration of propranolol in both Purkinje and ventricular muscle fibers by 39.5% and 33.9%, respectively. These findings indicate that (a) low concentrations of propranolol produced no direct electrophysiological effect, and (b) high concentrations of propranolol produced several potential antiarrhythmic effects in addition to the previously reported effects on Vmax and the action potential duration.

Muscle responses of Thoroughbreds to conventional race training and detraining

Summary Ten healthy sedentary Thoroughbreds with previous race training experience were trained conventionally for 9 weeks. Muscle biopsy samples were obtained before and after training and after 6 weeks of detraining pasture rest. Biopsy samples were obtained from the right deltoid, triceps, vastus lateralis, middle gluteal, biceps femoris, and semitendinosus muscles. The deep-frozen biopsy samples were analyzed for activities of succinate dehydrogenase (sdh), 3-hydroxy-acylcoenzyme A dehydrogenase (had), and phosphorylase (phos) and for glycogen concentration. The triceps and gluteal muscle samples were also serially sectioned and stained for myofibrillar actomyosin adenosine triphosphatase (ATPase) activity after alkaline (pH 10.3) and sequential acidic (pH 4.34) ATPase inactivation. Fiber types I (alkaline preincubation), IIA1, IIA2, and IIA3 (sequential acidic preincubation over 5 minutes) were identified and were evaluated for fiber-type distribution and fiber areas. Increases in response to training were observed in deltoid and vastus muscle sdh and gluteal muscle had activities, and deltoid muscle glycogen concentration (P < 0.05 to P < 0.01). Changes in phos activity were not observed. Type-IIA1, -IIA2, and -IIA3 fiber areas in triceps muscle were increased in response to training (P < 0.05 to P < 0.01). Changes in fiber-type distribution did not occur in response to training. Changes in muscle enzyme activities, glycogen concentration, fiber types, and fiber areas were not seen from posttraining to detraining. Further increases were observed when detraining values were compared with pretraining values in deltoid, triceps, vastus, gluteal, and biceps femoris muscle sdh activities and in gluteal muscle glycogen concentration (P < 0.05 to P < 0.01). It was concluded that the predominant failure to detect training-induced muscle enzyme changes, along with documentation of increases in fast-twitch muscle fiber areas, indicate that conventional Thoroughbred training is principally of a sprinting nature. A greater emphasis on longer, slow endurance work early in training might add greatly to Thoroughbred horses’ abilities to withstand the rigors of sprint training.

Fiber-type composition of nine rat muscles. I. Changes during the first year of life

There are few data available that describe the changes in fiber-type profiles with age in a range of muscles; thus fiber-type profiles and areas were determined in nine muscles of female rats from weaning to 1 yr. The results not only demonstrated the difference in fiber-type composition, size, and hence functional area in the various muscles examined but also illustrated the changes in these parameters with age. In particular, it was clear that two ends of a spectrum of fiber compositions are represented in the muscles studied: tensor fasciae latae, mainly fast-twitch glycolytic at one end and soleus (and adductor longus), mainly slow-twitch oxidative at the other; the remaining muscles were mostly dominated by fast-twitch fibers of a variety of metabolic types. Aging resulted in an increase in fiber area that was most dramatic in fast-twitch glycolytic fibers. Changes in fiber type with age were noted in all muscles, but the exact nature of the developmental changes appeared muscle specific.

Effect of the repartitioning agent cimaterol on growth, carcass and skeletal muscle characteristics in lambs.

Ten crossbred (Suffolk X Rambouillet) whether lambs were randomly assigned to receive 0 or 10 ppm cimaterol (CIM) in a completely mixed high-concentrate diet for 8 wk. Total weight gain and feed efficiency were improved 29% (P less than .05) and 14%, respectively, in the CIM-fed group. CIM also improved (P less than .01) dressing percent by 4.9 percentage points and improved yield grade by one grade. CIM increased longissimus muscle (LD) area 38% (P less than .01) and the yield of four lean cuts 28% (P less than .01). No difference was found in the proportion of type I (slow-contracting, oxidative) and type II (fast-contracting, mixed glycolytic/oxidative) fibers in LD and semitendinosus (ST) muscles between control and CIM groups, indicating no change in fiber type. The cross-sectional area of type II fibers in LD and ST muscles of the CIM group was 2,081 and 1,951 micron 2 as compared with 1,391 and 1,296 micron2 of the control group, respectively. The increase was approximately 50% (P less than .01). No difference was found in cross-sectional area of type I fibers, indicating that the increase of muscle mass was due to hypertrophy of type II fibers only. DNA concentration (micrograms/g wet muscle or microgram/g protein) of CIM muscle was much lower (P less than .01) than that of control muscle, suggesting that the protein accretion in muscle was accomplished without additional incorporation of nuclei from satellite cells.

Effect of Duchenne muscular dystrophy on enzymes of energy metabolism in individual muscle fibers

Individual muscle fibers from patients with Duchenne muscular dystrophy at an early stage in their disease, and from apparently normal boys of similar age, were analyzed for 13 enzymes of energy metabolism. This approach avoided the serious problems with muscle homogenate assays from increases in nonparenchymal components and permitted assessment of disease changes in different fiber types. Some enzymes of glycogenolysis (phosphorylase, phosphoglucomutase, and pyruvate kinase) were decreased in dystrophic fibers of all types. Phosphofructokinase was decreased in presumptive type II fibers. Lactate dehydrogenase was increased in type I fibers and essentially unchanged in type II. Phosphoglucoisomerase was near normal. Two enzymes of glucose metabolism not involved in glycogenolysis, hexokinase and glycogen synthase, were near normal, but a third, fructose bisphosphatase, was sharply reduced. Two enzymes of oxidative metabolism, citrate synthase, and β-hydroxyacyl CoA dehydrogenase, were unchanged or increased. Two enzymes of high energy phosphate transfer, creatine kinase and adenylokinase, were only marginally affected. The net result is to leave the type II fibers, which normally exert the greatest force, with a severe deficit in the glycogenolytic enzyme machinery to maintain that force.

Fiber type and fiber size changes in selected thigh muscles six months after low thoracic spinal cord transection in adult cats: Exercise effects

The effects of low thoracic spinal cord transection on muscle weights, fiber type compositions and, fiber cross-sectional areas of selected hind limb muscles were studied. Adult cats were spinalized at T12 and maintained for approximately 6 months. Some spinalized cats were exercised on a treadmill 30 min/day, 5 days/week to determine the role of weight support in maintaining the muscle properties. Spinalization resulted in a significant decrease in the weights of most extensors, whereas the flexors or those that act as both flexors and extensors were maintained near control values. All muscles showed a significant increase in the percentage of fast-twitch fibers and decrease in slow oxidative fibers following spinalization. In addition, the predominant fast fiber type in each muscle tended to have the largest decrease in cross-sectional area in the spinalized cats. The atrophic and fiber type adaptations were less pronounced in the exercised cats. In contrast, the relative cross-sectional area of high oxidative fibers generally was similar among the three groups. These results demonstrated that the muscles below the level of the lesion became more “fast-like” histochemically following spinal cord transection, whereas the oxidative properties were relatively unaffected. Further, daily exercise involving weight support appeared to be an important deterrent to these atrophic responses, particularly in the muscles that normally have a postural function (i.e., the slow extensors).

Promiscuous expression of myosin in myotonic dystrophy.

The pathologic changes in myotonic dystrophy (DM) skeletal muscle biopsies have been analyzed at both the histochemical and molecular level. A histochemical stain for pretyping single fibers in conjunction with sodium dodecyl sulphate-polyacrylamide gel electrophoresis allowed biochemical differences to be pinpointed in specific histochemical fiber types. These biochemical differences can be related to histochemical changes in fiber type observed in cross-section of the DM biopsies. Such changes included specific fiber type atrophy, hypertrophy, and disproportion. The pathogenesis of DM appears to be characterized by a large increase in the number of promiscuous fibers, that is, those fibers that express both fast and slow myosins. This promiscuity, which is rare in control muscle (less than 2%), is also prevalent at high levels in some family members at risk for DM. The observed promiscuity, although probably not a primary effect of DM, appears to be linked to the histochemical changes in fiber type observed in the DM biopsies.

Long-term effects of spinal cord transection on fast and slow rat skeletal muscle: II. Morphometric properties

Morphometric properties of rat soleus and extensor digitorum longus muscles were studied 1 year following complete thoracic spinal cord transection (spinal cord level T9). Both muscles demonstrated almost complete type 1 to type 2 muscle fiber type conversion after 1 year. Muscle fiber atrophy was observed in both muscles. Type 2 fiber atrophy occurred to about the same extent in both muscles. Atrophy was most severe for the soleus type 1 fibers (50% decrease in size). Calculations based on the fiber type and size changes observed indicate that the percentage of the muscle cross-sectional area occupied by each fiber type was almost the same for both muscles 1 year after transection. Discriminant analysis of the data indicated that the percentage of type 2 fibers present in the muscle was the best discriminator between the various groups. These morphometric data provided a basis for understanding the contractile results presented in the previous study as well as insights into the mechanism of transformation in skeletal muscle. Furthermore, inherent differences between type 1 and type 2 fibers were demonstrated between predominantly slow and predominantly fast muscles. Thus, after almost one-half a lifetime of transection, rat muscles are almost completely transformed to fast muscle, and, regardless of initial conditions, have nearly identical properties.

Protein profiles of sarcoplasmic reticulum from normal and dystrophic mouse muscle

Sarcoplasmic reticulum (SR) was isolated from skeletal muscle of dystrophic (C57BL/6J dy 2J/dy 2J) mice and the protein composition analysed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Densitometric analysis of dystrophic SR preparations indicated a decrease in the Ca 2+-ATPase and calsequestrin, and the appearance of a protein with molecular weight 72000. These differences in the protein profiles between normal and dystrophic SR became more apparent as the disease progressed. The observations are discussed in relation to secondary changes in the dystrophic process such as changes in fibre type and the presence of immature fibres.

Muscle fiber type changes in human skeletal muscle after injuries and immobilization.

Eight athletes operated on for knee injuries were followed with muscle biopsies before and at various intervals after surgery and immobilization. A statistically significant change of the muscle fiber distribution was found. The percentage type I fibers dropped from an average of 54% to 43%. One competitive cross-country skier showed a dramatic drop from 81% type I fibers at surgery to 58% type I fibers six weeks later. After beginning training he returned to 85% type I fibers. One athlete who had been operated and immobilized for long periods several times showed a drastic difference in fiber type distribution between his two thighs with 20% type I fibers in the injured leg and 69% type I fibers in his uninjured leg. After three years of training his fiber type composition in the injured leg returned toward the fiber type distribution of the uninjured thigh. It is evident that muscle fiber type composition can change. The most probable reason for this is that the drastic change from hard sports training to nearly complete immobilization influences both the muscle itself and its innervation and causes this change of fiber types.

Fiber type changes in rat skeletal muscle after intense interval training

Summary. Female Sprague-Dawley rats were subjected to a ten week training program to determine the influence of intense interval running on the fiber type composition of selected hindlimb muscles; soleus (S), plantaris (P), deep vastus lateralis (DVL), and superficial vastus lateralis (SVL). The muscles of one hindlimb were used for histochemical ATPase analysis to determine the distribution of fiber types and those of the contralateral hindlimb were assayed biochemically for citrate synthase activity (an aerobic marker). Training induced a significant increase in citrate synthase activity in each muscle section. The largest absolute increase occurred in the DVL and the largest relative increase occurred in the SVL. The distribution of fiber types within the S (85% slow-twitch) and SVL (100% fasttwitch) remained unchanged with training. However, significant increases in the percentage of type I (slow-twitch) fibers in both the P (2-fold) and DVL (3-fold) were observed with concomitant decreases in the type II (fast-twitch) population. In addition, training induced significant changes in the fast-twitch subtype populations of the DVL (IIB IIA). These data suggest exercise-induced fiber type transformations occurring both within the fast-twitch population and between fast-twitch and slow-twitch fibers in certain hindlimb muscles of the rat following a high intensity interval training program.

Effects of chronic exercise during aging on muscle and end-plate morphology in rats.

Terminal sprouting, myofiber atrophy, and fiber type changes were studied in soleus and distal gastrocnemius muscles of 21- and 26-mo-old rats and in rats who performed treadmill running from 21 to 26 mo. End-plate structure and muscle fiber types were demonstrated by staining for acetylcholinesterase and myosin ATPase activity. Terminal sprouting was expressed as the percentage of end plates with growth configurations. Fiber atrophy was assessed as percentage of small-diameter fibers. In all three groups, the percentage of small-diameter fibers was significantly smaller and the percentage of growth configurations significantly larger in the soleus than in the gastrocnemius. The exercised-soleus group had a significantly higher percentage of growth configurations than the 26-mo controls, which had a higher percentage than the 21-mo controls. Percentages among gastrocnemius groups were not different. Fiber type was similar among gastrocnemius groups. However, the exercised-soleus had significantly more slow-twitch fibers than the controls. These data suggest that the soleus responds differently to chronic exercise during aging than does the gastrocnemius.

Relative independence of metabolic enzymes and neuromuscular activity.

Effects of spinal cord transection in 2-wk-old cats on the metabolic, histochemical, and fatigue properties of a fast- and a slow-twitch muscle were determined. Chronic (6-12 mo) spinalization (Sp) resulted in an increased ratio of fast-twitch, oxidative-glycolytic (FOG) to slow-twitch, oxidative (SO) fibers in soleus (SOL). In medial gastrocnemius (MG), Sp produced a histochemical profile suggesting that fast fibers were increased at the expense of slow fibers. Changes in biochemical markers for oxidative (citrate synthase) and glycolytic (GPD) potential were consistent with the histochemical findings. The fatigue index of Sp MG and SOL remained normal and was consistent with the type and degree of fiber type change. Daily treadmill exercise did not markedly alter any of the adaptations. The metabolic and fatigue properties of skeletal muscle of Sp cats are consistent with the view that as some fibers develop "faster-like" characteristics, the oxidative and the glycolytic potential is also enhanced. As was true of the contractile properties and related biochemical data, the changes observed suggest that significant changes occurred within as well as across fiber types. These data, in conjunction with that of chronic EMG recordings, provide evidence that there is a relative independence of both the oxidative potential and the fatigability of a muscle relative to its quantity of activation.

Fiber type changes in rat skeletal muscle after intense interval training.

Female Sprague-Dawley rats were subjected to a ten week training program to determine the influence of intense interval running on the fiber type composition of selected hindlimb muscles; soleus (S), plantaris (P), deep vastus lateralis (DVL), and superficial vastus lateralis (SVL). The muscles of one hindlimb were used for histochemical ATPase analysis to determine the distribution of fiber types and those of the contralateral hindlimb were assayed biochemically for citrate synthase activity (an aerobic marker). Training induced a significant increase in citrate synthase activity in each muscle section. The largest absolute increase occurred in the DVL and the largest relative increase occurred in the SVL. The distribution of fiber types within the S (85% slow-twitch) and SVL (100% fast-twitch) remained unchanged with training. However, significant increases in the percentage of type I (slow-twitch) fibers in both the P (2-fold) and DVL (3-fold) were observed with concomitant decreases in the type II (fast-twitch) population. In addition, training induced significant changes in the fast-twitch subtype populations of the DVL (IIB----IIA). These data suggest exercise-induced fiber type transformations occurring both within the fast-twitch population and between fast-twitch and slow-twitch fibers in certain hindlimb muscles of the rat following a high intensity interval training program.

Central core degeneration after tenotomy in soleus muscles of hyperthyroid rats

Tenotomy of the rat soleus muscle is followed by a central degeneration of slow, fatigue-resistant muscle fibers. Previous experiments showed that fast, fatigable fibers of the gastrocnemius when transformed to slow, fatigue-resistant fibers by cross-reinnervation also develop lesions after tenotomy. The experiments described in this communication were carried out to discover whether the susceptibility of fibers to lesions was determined by their fiber type or the nature of their innervation. Rats were rendered hyperthyroid by the administration of sodium 3,3′,5-triiodo- l-thyronine (T 3) for 7 to 10 weeks. Tenotomy of the soleus muscles was then carried out and the experimental and contralateral muscles were removed and stained for myosin ATPase activity after a further 2 weeks. The hyperthyroid state of each animal was confirmed by the assay of succinate dehydrogenase activity of liver and the contralateral muscle. After acid preincubation, whole muscle fiber type counts of contralateral muscles showed a statistically significant change from a predominantly acid-stable population of fibers to acid-labile fibers. In addition, many fibers of intermediate staining properties were seen. When the experimental muscles were examined, all three varieties of fiber showed central degeneration. The nature of the fiber type change induced by T 3 and the role that innervation might play in this is discussed. It was concluded that the susceptibility of fibers to the lesions that follow tenotomy is dependent on the nature of their innervation rather than their fiber type.

Fiber type changes in denervated soleus muscles of the hyperthyroid rat

The thyroid status of rats is known to influence the histochemical and biochemical myosin adenosine triphosphatase (M-ATPase) activity of the soleus muscle. In the hypothyroid state, denervated soleus muscles are not subject to that influence. Our experiments indicated that in the hyperthyroid state fibers of the denervated soleus muscle show a profound change from acid-stable M-ATPase positive to acid-stable M-ATPase negative. We concluded that this change was induced by the hyperthyroid state and was not neurally mediated.

Training-induced morphological and functional changes in skeletal muscle.

In addition to the histochemical ATPase staining techniques, immunohistochemistry and two-dimensional gel electrophoresis lead to a better understanding of the molecular structure of the contractile proteins actin, myosin, tropomyosin, and troponin in the different fiber types of human skeletal muscle. A great plasticity enables muscle fibers to adapt to different genetic and environmental influences not only on the level of cellular ultrastructure and metabolic function, but also on the molecular level of the contractile proteins. Fiber type transformation is possible with cross-innervation and specific electrical stimulation. Prolonged and intense endurance training probably also transforms type II fibers into type I fibers, whereas with spring or strength training changes in the different fiber types are restricted to ultrastructure (e.g., myofibrillar to mitochondrial volume ration) and metabolic function. The fiber type distribution pattern in top athletes seems to be determined by both hereditary and environmental factors.