Citrate synthase expression and enzyme activity after endurance training in cardiac and skeletal muscles.

The present study was designed to examine the acute and chronic effects of endurance treadmill training on citrate synthase (CS) gene expression and enzymatic activity in rat skeletal and cardiac muscles. Adult rats were endurance trained for 8 wk on a treadmill. They were killed 1 h (T(1), n = 8) or 48 h (T(48), n = 8) after their last bout of exercise training. Eight rats were sedentary controls (C) during the training period. CS mRNA levels and enzymatic activities of the soleus and ventricle muscles were determined. Training resulted in higher CS mRNA levels in both the soleus muscles (21% increase in T(1); 18% increase in T(48), P < 0.05) and ventricle muscles (23% increase in T(1); 17% increase in T(48), P < 0.05) when compared with the C group. The CS enzyme activities were 42 (P < 0.01) and 25% (P < 0.01) greater in the soleus muscles of T(1) and T(48) groups, respectively, when compared with that of the C group. Soleus CS enzyme activity was significantly greater in the T(1) vs. T(48) groups (P < 0.05). However, no appreciable alterations in CS enzyme activities were observed in the ventricle muscles in both training groups. These findings suggest differential responses of skeletal and cardiac muscles in CS enzymatic activity but similar responses in CS gene expression at 1 and 48 h after the last session of endurance training. Moreover, our data support the existence of an acute effect of exercise on the training-induced elevation in CS activity in rat soleus but not ventricle muscles.     

Neuronal adaptation of corticospinal mechanisms of muscle contraction regulation in athletes

Adaptation changes in the corticospinal mechanisms of muscle contraction control in athletes were investigated. Using the transcranial magnetic stimulation method, the parameters of motor evoked potentials of skeletal muscles of the lower limbs during voluntary static loads of various intensities and durations were measured. Athletes, as compared to the reference group, exhibited a greater increase in the maximal amplitude of the motor evoked potentials of the skeletal muscles of the lower limbs, a smaller decrease in the central motor conduction time of nerve pulses and the peripheral period in electromyograms, and a smaller increase in the cortical and segmental silent periods with increasing intensity and duration of isometric muscle contractions. The mechanisms of adaptation of corticospinal regulation of human muscle contraction to specific conditions of extreme motor activities are discussed.     

Differential adaptations during growth spurt and in young adult rat muscles

During the post-weaning growth and maturation period (25/90 days after birth), rat limb muscles are submitted to specific adaptations. Our aim was to characterize the mechanical properties of two muscles that are opposite in terms of fibre-type distribution, the soleus and the extensor digitorum longus (EDL) muscles of male Wistar rats. Results showed a fast-to-slow fibre-type transition in soleus while no modification in fibre-type distribution was observed in EDL. A growth-induced increase in muscle force was observed. Soleus underwent an increase in twitch kinetics, but EDL showed no modification. Resistance to fatigue was higher in 90-day-old soleus but not modified in the EDL. Surprisingly, analysis of maximal shortening velocity showed a decrease in both soleus and EDL. Finally, tension/extension curves indicated a growth-induced increase in series elastic stiffness in the two muscles. These results suggest that during this growth period, skeletal muscles are submitted to differential adaptations. Moreover, whereas adaptation of biomechanical properties observed can be explained partly by an adaptation of fibre profile in soleus, this is not the case for EDL. It is suggested that changes in muscle architecture, which are often disregarded, could explain some variations in mechanical properties, especially when muscles undergo an increase in both mass and length.     

Effects of aging and denervation on the expression of uncoupling proteins in slow- and fast-twitch muscles of rats

We investigated the effects of aging and denervation on the gene expression of uncoupling proteins (UCPs) in slow-twitch soleus and fast-twitch gastrocnemius muscles. In a comparison between the control limbs of 6- and 24-month-old rats, the mRNA levels of UCP3, heart-type fatty acid binding protein (HFABP), and glucose transporter-4 (GLUT4) were considerably lower in the gastrocnemius muscles of the older rats, whereas no significant differences in the mRNA levels of those genes as well as UCP2 and cytochrome oxidase subunit IV (COX-IV) were observed in the soleus muscles of young and old rats. The UCP3 and COX-IV protein levels were also reduced considerably in the aged gastrocnemius muscles with atrophy. Denervation of the sciatic nerve caused an increase in UCP3 mRNA levels in both muscles, but the regulation of other genes contrasted between the two types of skeletal muscles. In spite of the increased mRNA level, a remarkable reduction in UCP3 protein was found in the denervated gastrocnemius muscles. These results indicate that the effects of aging and denervation on the gene expression of UCPs, HFABP, GLUT4, and COX-IV are different between the muscle types. The reduction in the mitochondrial UCP3 and COX proteins in aged fast-twitch muscles may have a negative effect on energy metabolism and thermogenesis in old animals.     

Thyroid hormone regulation of MHC isoform composition and myofibrillar ATPase activity in rat skeletal muscles.

Myosin heavy chain (MHC) isoform composition and Ca2+ Mg2+ dependent ATPase activity were determined in myofibrils prepared from skeletal muscles (diaphragm, soleus, plantaris and tibialis anterior) of euthyroid (C), hypothyroid (Tx) and hyperthyroid (T3) rats. Direct comparison between T3 and Tx gave an indication of the maximal effect of thyroid hormones. Significant differences in MHC-1 and MHC-2B proportions and in ATPase activity were found in all muscles. The difference in MHC-2A/X proportion was significant only in soleus, diaphragm and plantaris. When T3 and C were compared, significant variations in MHC isoform composition were found only in plantaris and diaphragm. The comparison between Tx and C showed significant differences in MHC isoform distribution and in ATPase activity in most muscles. The differences in ATPase activity among muscles and among thyroid states were consistent with those in MHC isoform distribution. From the correlations between ATPase activity and MHC isoform distribution the enzymatic activities of individual MHC isoforms were calculated. The results indicate that MHC isoform distribution is controlled by thyroid state in all skeletal muscles and that changes in MHC isoforms distribution are accompanied by proportional changes in ATPase activity.     

Regulation of skeletal muscle dihydropyridine receptor gene expression by biomechanical unloading.

Biomechanical unloading of the rat soleus by hindlimb unweighting is known to induce atrophy and a slow- to fast-twitch transition of skeletal muscle contractile properties, particularly in slow-twitch muscles such as the soleus. The purpose of this study was to determine whether the expression of the dihydropyridine (DHP) receptor gene is upregulated in unloaded slow-twitch soleus muscles. A rat DHP receptor cDNA was isolated by screening a random-primed cDNA lambda gt10 library from denervated rat skeletal muscle with oligonucleotide probes complementary to the coding region of the rabbit DHP receptor cDNA. Muscle mass and DHP receptor mRNA expression were assessed 1, 4, 7, 14, and 28 days after hindlimb unweighting in rats by tail suspension. Isometric twitch contraction times of soleus muscles were measured at 28 days of unweighting. Northern blot analysis showed that tissue distribution of DHP receptor mRNA was specific for skeletal muscle and expression was 200% greater in control fast-twitch extensor digitorum longus (EDL) than in control soleus muscles. A significant stimulation (80%) in receptor message of the soleus was induced as early as 24 h of unloading without changes in muscle mass. Unloading for 28 days induced marked atrophy (control = 133 +/- 3 vs. unweighted = 62.4 +/- 1.8 mg), and expression of the DHP receptor mRNA in the soleus was indistinguishable from levels normally expressed in EDL muscles. These changes in mRNA expression are in the same direction as the 37% reduction in time to peak tension and 28% decrease in half-relaxation time 28 days after unweighting. Our results suggest that muscle loading necessary for weight support modulates the expression of the DHP receptor gene in the soleus muscle.     

The effect of heat stress on skeletal muscle contractile properties

An elevated heat-shock protein (HSP) content protects cells and tissues, including skeletal muscles, from certain stressors. We determined if heat stress and the elevated HSP content that results is correlated with protection of contractile characteristics of isolated fast and slow skeletal muscles when contracting at elevated temperatures. To elevate muscle HSP content, one hindlimb of Sprague–Dawley rats (21–28 days old, 70–90 g) was subjected to a 15 min 42 °C heat-stress. Twenty-four hours later, both extensor digitorum longus (EDL) and soleus muscles were removed, mounted in either 20 °C or 42 °C Krebs-Ringer solution, and electrically stimulated. Controls consisted of the same muscles from the contra-lateral (non-stressed) hindlimbs as well as muscles from other (unstressed) animals. Isolated muscles were twitched and brought to tetanus every 5 min for 30 min. As expected, HSP content was elevated in muscles from the heat-stressed limbs when compared with controls. Regardless of prior treatment, both EDL and soleus twitch tensions were lower at 42 °C when compared with 20 °C. In addition, when incubated at 42 °C, both muscles showed a drop in twitch tension between 5 and 30 min. For tetanic tension, both muscles also showed an increase in tension between 5 and 30 min when stimulated at 20 °C regardless of treatment but when stimulated at 42 °C no change was observed. No protective effect of an elevated HSP content was observed for either muscle. In conclusion, although heat stress caused an elevation in HSP content, no protective effects were conferred to isolated contracting muscles.     

Effects of high-intensity training on MCT1, MCT4, and NBC expressions in rat skeletal muscles: influence of chronic metabolic alkalosis

This study investigated the effects of high-intensity training, with or without induced metabolic alkalosis, on lactate transporter (MCT1 and MCT4) and sodium bicarbonate cotransporter (NBC) content in rat skeletal muscles. Male Wistar rats performed high-intensity training on a treadmill 5 times/wk for 5 wk, receiving either sodium bicarbonate (ALK-T) or a placebo (PLA-T) prior to each training session, and were compared with a group of control rats (CON). MCT1, MCT4, and NBC content was measured by Western blotting in soleus and extensor digitorum longus (EDL) skeletal muscles. Citrate synthase (CS) and phosphofructokinase (PFK) activities and muscle buffer capacity (betam) were also evaluated. Following training, CS and PFK activities were significantly higher in the soleus only (P < 0.05), whereas betam was significantly higher in both soleus and EDL (P < 0.05). MCT1 (PLA-T: 30%; ALK-T: 23%) and NBC contents (PLA-T: 85%; ALK-T: 60%) increased significantly only in the soleus following training (P < 0.01). MCT4 content in the soleus was significantly greater in ALK-T (115%) but not PLA-T compared with CON. There was no significant change in protein content in the EDL. Finally, NBC content was related only to MCT1 content in soleus (r = 0.50, P < 0.01). In conclusion, these results suggest that MCT1, MCT4, and NBC undergo fiber-specific adaptive changes in response to high-intensity training and that induced alkalosis has a positive effect on training-induced changes in MCT4 content. The correlation between MCT1 and NBC expression suggests that lactate transport may be facilitated by NBC in oxidative skeletal muscle, which may in turn favor better muscle pH regulation.     

Reduced T2* Values in Soleus Muscle of Patients with Type 2 Diabetes Mellitus

Tissue water transverse relaxation times (T2) are highly sensitive to fluid and lipid accumulations in skeletal muscles whereas the related T2* is sensitive to changes in tissue oxygenation in addition to factors affecting T2. Diabetes mellitus (DM) affects muscles of lower extremities progressively by impairing blood flow at the macrovascular and microvascular levels. This study is to investigate whether T2 and T2* are sensitive enough to detect abnormalities in skeletal muscles of diabetic patients in the resting state. T2 and T2* values in calf muscle of 18 patients with type 2 DM (T2DM), 22 young healthy controls (YHC), and 7 age-matched older healthy controls (OHC) were measured at 3T using multi-TE spin echo and gradient echo sequences. Regional lipid levels of the soleus muscle were also measured using the Dixon method in a subset of the subjects. Correlations between T2, T2*, lipid levels, glycated hemoglobin (HbA1c) and presence of diabetes were evaluated. We found that T2 values were significantly higher in calf muscles of T2DM subjects, as were T2* values in anterior tibialis, and gastrocnemius muscles of T2DM participants. However, soleus T2* values of the T2DM subjects were significantly lower than those of the older, age-matched HC cohort (22.9±0.5 vs 26.7±0.4 ms, p<0.01). The soleus T2* values in the T2DM cohort were inversely correlated with the presence of diabetes (t = −3.46, p<0.001) and with an increase in HbA1c, but not with body mass index or regional lipid levels. Although multiple factors may contribute to changes in T2* values, the lowered T2* value observed in the T2DM soleus muscle is most consistent with a combination of high oxygen consumption and poor regional perfusion. This finding is consistent with results of previous perfusion studies and suggests that the soleus in individuals with T2DM is likely under tissue oxygenation stress.     

Adrenal hormones enhance glycogenolysis in nonexercising muscle during exercise

The purpose of this study was to investigate whether epinephrine exerts an effect on glycogen metabolism in nonexercising (Non-Ex) as well as in exercising (Ex) skeletal muscle. Rats ran (15 m/min; 8% grade) on their forelimbs while their hindlimbs (Non-Ex) were suspended above the treadmill. Electromyographic records confirmed the lack of significant contractile activity in muscles during suspension. Plasma epinephrine levels were manipulated in three experimental groups (n = 20 for each group): adrenalectomized (ADX), intact adrenals (IA), and IA + epinephrine injection (+Ep). Another group of rats performed normal exercise on all four limbs (15 m/min; 8% grade). Muscle glycogen levels were measured in selected hindlimb muscles at t = 0 and after 90 min exercise (15 m/min; 8% grade) or suspended rest. In the absence of epinephrine (ADX), no glycogen loss was found (P greater than 0.05) in Non-Ex muscles during the exercise period. In the IA group (epinephrine levels elevated sixfold above basal at t = 90 min), glycogen levels in the nonexercising soleus, plantaris, and red and white gastrocnemius were significantly (P less than 0.05) depleted to 62 +/- 6, 67 +/- 6, 58 +/- 5, and 67 +/- 9% of control values, respectively. Similar decrements occurred in these muscles when exercise was performed on all four limbs (P greater than 0.05). We conclude that glycogenolysis occurs in nonexercising skeletal muscle independent of contractile activity, probably due to the effect of epinephrine. Furthermore, the present data strongly suggest that glycogen depletion patterns in muscles during exercise cannot be used as an index of motor unit recruitment.     

Proteomic analysis of rat soleus muscle undergoing hindlimb suspension-induced atrophy and reweighting hypertrophy

A proteomic analysis was performed comparing normal rat soleus muscle to soleus muscle that had undergone either 0.5, 1, 2, 4, 7, 10 and 14 days of hindlimb suspension-induced atrophy or hindlimb suspension-induced atrophied soleus muscle that had undergone 1 hour, 8 hour, 1 day, 2 day, 4 day and 7 days of reweighting-induced hypertrophy. Muscle mass measurements demonstrated continual loss of soleus mass occurred throughout the 21 days of hindlimb suspension; following reweighting, atrophied soleus muscle mass increased dramatically between 8 hours and 1 day post reweighting. Proteomic analysis of normal and atrophied soleus muscle demonstrated statistically significant changes in the relative levels of 29 soleus proteins. Reweighting following atrophy demonstrated statistically significant changes in the relative levels of 15 soleus proteins. Protein identification using mass spectrometry was attempted for all differentially regulated proteins from both atrophied and hypertrophied soleus muscle. Five differentially regulated proteins from the hindlimb suspended atrophied soleus muscle were identified while five proteins were identified in the reweighting-induced hypertrophied soleus muscles. The identified proteins could be generally grouped together as metabolic proteins, chaperone proteins and contractile apparatus proteins. Together these data demonstrate that coordinated temporally regulated changes in the skeletal muscle proteome occur during disuse-induced soleus muscle atrophy and reweighting hypertrophy.     

Morphological and biochemical changes in old rat muscles: effect of increased use

Male Wistar rats were strength and swim trained during a substantial period of old age to determine the influence of aging and activity on the histochemical and metabolic characteristics of a predominantly slow (soleus) and a predominantly fast (plantaris) skeletal muscle. Strength training counteracted the age-related atrophy of the fibers and the age-induced changes in fiber-type distribution of both muscles. Swim training, on the other hand, was without any effect on these parameters. The activity of both mitochondrial and cytoplasmic enzymes became lower with aging in the soleus muscle, whereas only the activity of the cytoplasmic enzymes became lower in the plantaris. Strength training reduced the aerobic capacity of both muscles, whereas swim training had the opposite effect. Aging induced a lower glycogen concentration of the lateral gastrocnemius muscle. This was avoided by swim training. The phosphocreatine and adenosine 5'-triphosphate concentrations were unchanged with aging but became higher with strength training. The activity pattern, therefore, seems to have a considerable influence on the age-related modification of the histochemical and metabolic characteristics of skeletal muscles of the rat. The effect, however, is related to the recruitment pattern of the fiber populations and the form of activity.     

Increased DNA fragmentation and altered apoptotic protein levels in skeletal muscle of spontaneously hypertensive rats.

Apoptosis is a highly conserved process that plays an important role in controlling tissue development, homeostasis, and architecture. Dysregulation of apoptosis is a hallmark of numerous human pathologies including hypertension. In the present work we studied the effect of hypertension on apoptosis and the expression of several apoptotic signaling and/or regulatory proteins in four functionally and metabolically distinct muscles. Specifically, we examined these markers in soleus, red gastrocnemius, white gastrocnemius, and left ventricle (LV) of 20-wk-old normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Compared with WKY rats SHR had a significantly greater heart weight, LV weight, and mean arterial pressure. In general, SHR skeletal muscle had increased Bax protein, procaspase-3 protein, caspase-3 activity, cleaved poly(ADP-ribose) polymerase protein, and DNA fragmentation as well as decreased Bcl-2 protein and a lower Bcl-2-to-Bax ratio. Subcellular distribution studies demonstrated increased levels of apoptosis-inducing factor protein in cytosolic or nuclear extracts as well as elevated nuclear Bax protein in SHR skeletal muscle. Moreover, heat shock protein 70 in red gastrocnemius and soleus was significantly correlated to several apoptotic factors. With the exception of lower heat shock protein 90 levels in SHR no additional differences in any apoptotic markers were observed in LV between groups. Collectively, this report provides the first evidence that apoptotic signaling is altered in skeletal muscle of hypertensive animals, an effect that may be mediated by both caspase-dependent and -independent mechanisms. This proapoptotic state may provide some understanding for the morphological and functional abnormalities observed in skeletal muscle of hypertensive animals.     

Changes in fiber composition of soleus muscle during rat hindlimb suspension

Chronic reduction of gravitational load in the rear limbs of rats to simulate the influence of near-zero gravity in skeletal muscles has been shown previously to elicit atrophy in the soleus muscle. Use of this model by the present investigation indicates that soleus atrophy was characterized by a decline in the number of fibers in groups that contained the slow isoenzyme of myosin and which were classified as type I from intensity of staining to myofibrillar actomyosin adenosinetriphosphatase (ATPase) and to NADH tetrazolium reductase. Furthermore total fiber number was not changed, whereas fibers containing the intermediate isoenzyme and those classified as type IIa increased. There results could be explained by either a change in the composition within existing fibers or a simultaneous loss of slow fibers and de novo synthesis of intermediate and fast fibers. Evidence for transformation included an absence of embryonic or neonatal myosin in muscles from suspended rats and the constant fiber number that was unchanged by 4 wk of suspension. Furthermore although fiber areas of both groups of type I and IIa fibers declined during suspension, variability of the fiber areas within each group did not increase.     

Difference in thiamine metabolism between extensor digitorum longus and soleus muscles

1. Thiamine diphosphate level was higher in soleus muscle than in extensor digitorum longus muscle in various animals, whereas thiamine triphosphate level was less in the former muscle than in the latter except for mouse. 2. 2-Oxoglutarate dehydrogenase, transketolase and thiamine pyrophosphokinase activities were higher in soleus muscle than in extensor digitorum longus in rat and guinea pig. 3. The differences between rat two muscle phenotypes in thiamine diphosphate, but not thiamine triphosphate, level and the thiamine-related enzyme activities disappeared after denervation. 4. Tenotomy had little effect on thiamine phosphate levels and the thiamine-related enzyme activities in rat skeletal muscles.     

Seven skeletal muscles rich in slow muscle fibers may function to sustain neutral position in the rodent hindlimb

Skeletal muscles consist of slow-twitch and fast-twitch muscle fibers, which have distinct physiological and biochemical properties. The muscle fiber composition determines the contractile velocity and fatigability of a particular skeletal muscle. We analyzed the systemic distribution of slow muscle fibers in all rodent skeletal muscles by myosin ATPase staining and found that only seven hindlimb skeletal muscles were extremely rich in slow muscle fibers. These included the mouse piriformis (56.5%), gluteus minimus (35.7%), vastus intermedius (24.7%), quadratus femoris (69.9%), adductor brevis (44.3%), gracilis (24.6%), and soleus muscles (35.1%). In mice, the relative proportion of slow muscle fibers did not exceed 15% in skeletal muscles in other regions. The distribution of slow muscle fibers was well conserved in rats and rabbits. The soleus muscle is an important antigravity muscle in both rodents and humans; therefore, these skeletal muscles rich in slow muscle fibers might play an important role in sustaining neutral alignment of the lower extremity.     

PGC-1α and FOXO1 mRNA levels and fiber characteristics of the soleus and plantaris muscles in rats after hindlimb unloading

Fifteen-week-old rats were subjected to unloading induced by hindlimb suspension for 3 weeks. The peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) and forkhead box-containing protein O1 (FOXO1) mRNA levels and fiber profiles of the soleus and plantaris muscles in rats subjected to unloading (unloaded group) were determined and compared with those of age-matched control rats (control group). The body weight and both the soleus and plantaris muscle weights were lower in the unloaded group than in the control group. The PGC-1α mRNA was downregulated in the soleus, but not in the plantaris muscle of the unloaded group. The FOXO1 mRNA was upregulated in both the soleus and plantaris muscles of the unloaded group. The oxidative enzyme activity was reduced in the soleus, but not in the plantaris muscle of the unloaded group. The percentage of type I fibers was decreased and the percentages of type IIA and IIC fibers were increased in the soleus muscle of the unloaded group, whereas there was no change in fiber type distribution in the plantaris muscle of the unloaded group. Atrophy of all types of fibers was observed in both the soleus and plantaris muscles of the unloaded group. We conclude that decreased oxidative capacity and fiber atrophy in unloaded skeletal muscles are associated with decreased PGC-1α and increased FOXO1 mRNA levels.     

Skeletal muscle oxidative capacity, antioxidant enzymes, and exercise training

The purposes of this study were to determine whether exercise training induces increases in skeletal muscle antioxidant enzymes and to further characterize the relationship between oxidative capacity and antioxidant enzyme levels in skeletal muscle. Male Sprague-Dawley rats were exercise trained (ET) on a treadmill 2 h/day at 32 m/min (8% incline) 5 days/wk or were cage confined (sedentary control, S) for 12 wk. In both S and ET rats, catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPX) activities were directly correlated with the percentages of oxidative fibers in the six skeletal muscle samples studied. Muscles of ET rats had increased oxidative capacity and increased GPX activity compared with the same muscles of S rats. However, SOD activities were not different between ET and S rats, but CAT activities were lower in skeletal muscles of ET rats than in S rats. Exposure to 60 min of ischemia and 60 min of reperfusion (I/R) resulted in decreased GPX and increased CAT activities but had little or no effect on SOD activities in muscles from both S and ET rats. The I/R-induced increase in CAT activity was greater in muscles of ET than in muscles of S rats. Xanthine oxidase (XO), xanthine dehydrogenase (XD), and XO + XD activities after I/R were not related to muscle oxidative capacity and were similar in muscles of ET and S rats. It is concluded that although antioxidant enzyme activities are related to skeletal muscle oxidative capacity, the effects of exercise training on antioxidant enzymes in skeletal muscle cannot be predicted by measured changes in oxidative capacity.     

Acid phosphatase activity in soleus and plantaris muscle fibres of normal and dystrophic hamsters

Summary The activity of acid phosphatase in skeletal muscle fibres of the plantaris and soleus of normal and dystrophic male hamsters was quantified using a histochemical post-coupling semipermeable membrane technique. Althoug the absolute levels of activity were found to vary widely from one animal to another, the ratio of the mean activities in the two muscles in each animal was virtually constant. In normal muscles, the ratio was about 0.73 and in dystrophic muscles, about 0.77. The activity in plantaris muscle fibres was always significantly lower than that in the corresponding soleus fibres, and in normal fibres compared to dystrophic ones. Another difference was that in normal fibres the mean activity declined to a constant level in mature animals older than about 3 months. In contrast, the activity in dystrophic muscles appeared to fall exponentially throughout life. The functional significance of these findings is discussed.In honour of Prof. P. van Duijn     

Acid phosphatase activity in soleus and plantaris muscle fibres of normal and dystrophic hamsters. A quantitative histochemical study

The activity of acid phosphatase in skeletal muscle fibres of the plantaris and soleus of normal and dystrophic male hamsters was quantified using a histochemical post-coupling semipermeable membrane technique. Although the absolute levels of activity were found to vary widely from one animal to another, the ratio of the mean activities in the two muscles in each animal was virtually constant. In normal muscles, the ratio was about 0.73 and in dystrophic muscles, about 0.77. The activity in plantaris muscle fibres was always significantly lower than that in the corresponding soleus fibres, and in normal fibres compared to dystrophic ones. Another difference was that in normal fibres the mean activity declined to a constant level in mature animals older than about 3 months. In contrast, the activity in dystrophic muscles appeared to fall exponentially throughout life. The functional significance of these findings is discussed.