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PubMed1978

Free autografting of entire limb muscles in the cat: histochemistry and biochemistry.

Fifty extensor digitorium longus muscles of 25 cats were autografted, 33 with and 17 without prior denervation. After 50 days, no significant differences were observed between predenervated and nonpredenervated autografts. Autografted muscles weighed 48% of the weight of control muscles. Few original muscle fibers survived and within 2 wk autografts contained regenerating muscle fibers. The mean cross-sectional area of muscle fibers in the autografts reached 125% of the value for control nontransplanted muscles. The mean percentage of fibers classified high oxidative in autografted muscles was 67% of values for control muscles. SDH activity of autografted muscle homogenates reached 55% of control values. Up to 60 days after surgery autografts had only fast-twitch fibers. At 170 days autografts remained 95% fast twitch in composition. Revascularization began within 4 days, but the capillary to fiber ratio of long term autografts reached only 60% of control values. Although fiber hypertrophy suggests that cats use autografted muscles, lower than control succinate dehydrogenase activity may result from altered recruitment.

Action Potentials↗

PubMed1976

Effects of an anabolic steroid and sprint training on selected histochemical and morphological observations in rat skeletal muscle types.

The effects on selected histochemical and morphological parameters of anabolic steroid administration and of high-intensity sprint running, separately, and in combination, were studied in young adult male rats. Dianabol (methandrostenolone) 1 mg/day for 8 weeks had no significant effects on phosphorylase or glycogen staining intensities and on fiber area in skeletal muscles of either trained or sedentary animals. The program of sprint training resulted in significantly decreased intensities of phosphorylase in all ten regions of the gastrocnemius, plantaris, and soleus muscles that were studied. Glycogen localization was significantly increased with training in five regions of the gastrocnemius and plantaris muscles which contained predominantly fast-switch fibers. No changes in fiber area occurred with the training program. We conclude from these results that (a) normal androgen levels in young, healthy male animals are sufficiently high so that the intake of large doses of anabolic steroid does not result in the stimulation of glycogen metabolism or hypertrophy of skeletal muscle; (b) the changes induced by high-intensity, short-duration sprint training suggest that the existing glycolytic capacity of muscle is adequate to supply the muscles energy needs even during the stress of very strenous exercise, and that more fast-twitch fibers were recruited by the exercise regimen than slow-twitch fibers.

Animals↗

PubMed1976

Muscle fiber involvement during training of different intensities and durations.

The extent of skeletal muscle fiber type involvement during exercise training was evaluated by assessing the increase in oxidative markers in the muscles of rats trained by various exercise programs. Rats were trained by running 6 days/wk at 1 mph for 12 wk by one of four protocols: group I-10% grade, 2 h/day; group II-10% grade, 4 h/day; group III-30% grade, 40 min/day; and group IV-30% grade, 2 h/day. No distinction was found between the different programs for the increase in cytochrome c content or citrate synthase (CS) activity of mixed muscle. The more intense programs utilizing a 30% grade induced an increase in CS activity in the fast-twitch white (FTW) fiber that was twice that found in the 10% grade groups. The fast-twitch red (FTR) fibers of the 2 h/day or more groups showed a similar increase (90-95%) in CS activity except for the group that ran for only 40 min/day. These data suggest that: 1) running durations of moderately intense exercise longer than 2 h/day do not further increase the oxidative capacity of the working muscles; and 2) more intense exercise builds on the performance of previously used FTR fibers and additionally involves the low oxidative FTW fibers.

Animals↗

PubMed1992

Adenosine triphosphatases during maturation of cultured human skeletal muscle cells and in adult human muscle.

Na+/K(+)-ATPase, Mg(2+)-ATPase and sarcoplasmic reticulum (SR) Ca(2+)-ATPase are examined in cultured human skeletal muscle cells of different maturation grade and in human skeletal muscle. Na+/K(+)-ATPase is investigated by measuring ouabain binding and the activities of Na+/K(+)-ATPase and K(+)-dependent 3-O-methylfluorescein phosphatase (3-O-MFPase). SR Ca(2+)-ATPase is examined by ELISA, Ca(2+)-dependent phosphorylation and its activities on ATP and 3-O-methylfluorescein phosphate. Na+/K(+)-ATPase and SR Ca(2+)-ATPase are localized by immunocytochemistry. The activities of Na+/K(+)-ATPase and SR Ca(2+)-ATPase show a good correlation with the other assayed parameters of these ion pumps. All ATPase parameters investigated increase with the maturation grade of the cultured muscle cells. The number of ouabain-binding sites and the activities of Na+/K(+)-ATPase and K(+)-dependent 3-O-MFPase are significantly higher in cultured muscle cells than in muscle. The Mg(2+)-ATPase activity, the content of SR Ca(2+)-ATPase and the activities of SR Ca(2+)-ATPase and Ca(2+)-dependent 3-O-MFPase remain significantly lower in cultured cells than in muscle. The ouabain-binding constant and the molecular activities of Na+/K(+)-ATPase and SR Ca(2+)-ATPase are equal in muscle and cultured cells. During ageing of human muscle the activity as well as the concentration of SR Ca(2+)-ATPase decrease. Thus the changes of the activities of the ATPases are caused by variations of the number of their molecules. Na+/K(+)-ATPase is localized in the periphery of fast- and slow-twitch muscle fibers and at the sarcomeric I-band. SR Ca(2+)-ATPase is predominantly confined to the I-band, whereas fast-twitch fibers are much more immunoreactive than slow-twitch fibers. The presence of cross-striation for Na+/K(+)-ATPase and SR Ca(2+)-ATPase in highly matured cultured muscle cells indicate the development and subcellular organization of a transverse tubular system and SR, respectively, which resembles the in vivo situation.

Ca(2+) Mg(2+)-ATPase↗

PubMed1977

Compensatory hypertrophy of skeletal muscle fibers in streptozotocin-diabetic rats.

Previous studies have demonstrated an apparent differential response of the fiber types in mixed skeletal muscles of rats to streptozotocin diabetes. The purpose of the present study was to examine the ability of the different fiber types to hypertrophy in muscles from diabetic rats, which should further clarify the apparent differential trophic influence of insulin on the fibers. One group of rats was injected with streptozotocin to induce diabetes. The gastrocnemius muscle was then removed from one hindlimb of rats of both the diabetic and a second, normal group, resulting in compensatory growth of ipsilateral plantaris muscle. Rats were sacrificed 60 days following the surgery. Experimental muscles in normal and diabetic rats enlarged 79% and 61% over control muscles, respectively. In normal hypertrophied muscles there was an 8% increase in relative cross-sectional area composed of slow-twitch fibers, whereas in diabetic rats the slow-twitch component increased 17%. The results indicate that slow-twitch fibers in diabetic rats were capable of responding to the chronic power overloaded condition, but that the fast-twitch fibers had a reduced capacity to undergo compensatory growth. These findings support our previous observations suggesting that insulin may exert a differential trophic effect upon the muscle fiber types.

Animals↗

PubMed1977

Morphological and histochemical organization of the flexor carpi radialis muscle in the cat.

Most studies concerning the structure and function of skeletal muscle have utilized the hind limb of the experimental animal. However, it has been shown that the number of behavioral tasks performed by the cat's forelimb is greater than that of the hind limb. In addition, the forelimb muscles exhibit a functional complexity not observed in hind-limb musculature. The purpose of this study was to investigate the distribution of fast-twitch and slow-twitch muscle fibers and muscle spindles in the flexor carpi radialis muscle (FCR) and to correlate the distributional patterns in these structures with muscle tendon architecture and muscle function. It was found that the FCR, a wrist flexor, contains 37% slow-twitch fibers and 63% fast-twitch fibers. However, the slow-twitch fibers were concentrated in the deep region located between the tendons of origin and insertion, while the fast-twitch-glycolytic fibers were concentrated more peripherally. Muscle spindles were associated with the slow-twitch region and were never found in the region containing high concentrations of fast-twitch-glycolytic fibers. Fast-twitch-oxidative-glycolytic fibers were uniformly distributed throughout the muscle. It is proposed that the association of muscle spindles with slow-twitch fibers and the differential distribution of muscle fibers into slow-twitch and fast-twitch regions might allow these regions to function independently of one another when called upon to perform complex behavioral tasks.

Adenosine Triphosphatases↗

PubMed1976

Biochemical adaptations in skeletal muscle of trained thyroidectomized rats.

The cytochrome c concentrations of the different types of skeletal muscle of trained and nontrained normal and thyroidectomized rats were measured. Animals were trained by treadmill running 1 mph, at a 15% incline, 1 h/day, 5 days/wk for at least 12 wk. This training program induced an expected 50% increase in cytochrome c in the high-oxidative fast-twitch red (FTR) and slow-twitch red (STR) fibers and only a 25% increase in the low-oxidative fast-twitch white (FTW) fibers of the normal rats. This same training program caused a greater increase (100%) in the FTR and STR fibers of the thyroidectomized runners and a dramatic 243% increase in the FTW fiber. Even though the thyroidectomy procedure caused a reduction in oxidative capacity of all types of skeletal muscle fibers to about one-half normal, the absolute increase in cytochrome c in the muscles of the trained thyroidectomized animals was essentially the same or greater than that of the normal trained animals. These results indicate that the adaptive response to training of an increased oxidative capacity in skeletal muscle occurs in the absence of normal thyroid function. They also suggest that the exercise bouts of the thyroidectomized animals were performed with a relatively greater involvement of the FTW muscle fibers.

Adaptation, Physiological↗

PubMed1975

Effect of exercise on lipoprotein lipase activity in rat heart and skeletal muscle.

Lipoprotein lipase activity was measured in the three skeletal muscle fiber types of untrained rats and in those of rats subjected to a 12-wk program of treadmill running. Lipoprotein lipase activity in slow-twitch red fibers was approximately 14- to 20-fold higher (P less than 0.001) than that in fast-twitch white and approximately 2-fold higher (P less than 0.001) than that in fast-twitch red fibers in the untrained animals. These results suggest that, in sedentary animals, mainly slow-twitch red and fast-twitch red fibers are capable of taking up plasma triglyceride fatty acids. Regularly performed endurance exercise resulted in significant increase (2- to 4.5-fold) in lipoprotein lipase activity in the three muscle fiber types examined. The increase in lipoprotein lipase activity in response to treadmill running suggests that exercise increases the capacity of these fibers to take up and oxidize plasma triglyceride fatty acids. Cardiac muscle did not undergo an exercise-induced increase in the levels of activity of lipoprotein lipase similar to that seen in skeletal muscle.

Animals↗

PubMed1979

The influence of exercise on muscle lysosomal enzymes.

Representative lysosomal enzyme activities were measured in muscles taken 0 h and 24 h after an acute exercise run that was completed without any overt signs of fatigue. The animals had progressed 2 and 4 weeks into a standard exercise program which typically produces adaptive changes in the working muscles. There was an increase in acetylglucosaminidase activity (12%) in the fast-twitch red muscle section of all animals that participated in the training program. This small increase may be representative of a delayed response found after more exhausting exercise. The single exercise bout, however, did not cause any acute change in lysosomal activity nor alter the partition of lysosomal enzymes between the "free" and particulate fractions. Thus, altered lysosomal enzyme activity does not appear to be a contributing influence that challenges muscle fiber homeostasis during moderately intense running.

Acetylglucosaminidase↗

PubMed1976

Enzymatic changes in hypertrophied fast-twitch skeletal muscle.

Fast-twitch plantaris muscles of female rats were subjected to unilateral compensatory overload, induced by partial excision of synergistic muscles. One group of rats remained sedentary whereas another was subjected to a supplemental program of treadmill exercise consisting of walking 3 m/min, 65% grade, 2 h/day, 5 days/week. Groups of rats were sacrificed after 1, 2, 4, and 8 weeks and their muscles were weighed and analyzed for protein, citrate synthase, phosphofructokinase (PFK) and myofibril ATPase. Absolute and relative (muscle weight/body weight) muscle weights were much greater in both overloaded groups as compared to contralateral controls. However, treadmill exercise also increased the absolute and relative muscle mass of control plantaris muscles in the exercising group as compared tonormal sedentary contralateral controls. Citrate synthase activity was decreased in overloaded, sedentary muscles as compared to contralateral controls, but after 8 weeks of exercise, it returned to normal levels. PFK was decreased in both sedentary and exercised overloaded muscles throughout the 8 week period. Myofibril ATPase showed a tendency to be reduced in sedentary, overloaded muscles, and was significantly reduced in overloaded, exercising muscles. These results collectively suggest that certain fibers of overloaded fast-patterns take on similar in certain aspects to that normally seen in differentiated slow-twitch muscle fibers.

Adenosine Triphosphatases↗

PubMed1978

Further observations on myelinated axon numbers in normal and dystrophic mice.

Counts of the number of myelinated axons in the nerves to slow-twitch soleus and fast-twitch plantaris muscles of 129 ReJ dy/dy dystrophic mice at 4, 15 and 24 weeks of age have shown statistically significant reductions when compared to normal values. In addition muscle fibre losses had occurred in both muscles at the earliest age point studied. There was no suggestion of a progressive loss of myelinated axons. There was a greater percentage reduction in the soleus than in the plantaris nerves. The number of myelinated axons in the nerves to the plantaris and soleus muscles of the 129 ReJ +/+ normal animals was approximately the same, in contrast to the C57BL/6J strain where the soleus nerve always contained a greater number. Statistically significant reductions in the number of myelinated axons in the nerves to the medial gastrocnemius muscles of C57BL/6J dy2J/dy2J dystrophic mice have been observed at both 15 and 72 weeks of age. Muscle fibre losses have also been recorded in 72 weeks dystrophic medial gastrocnemius muscles.

Age Factors↗

PubMed1979

Mechanical efficiency of fast- and slow-twitch muscle fibers in man during cycling.

The influence of different percentages of slow-twitch (ST) and fast-twitch (FT) fibers in vastus lateralis on delta efficiency expressed by delta work (x)/delta energy liberation (y) in y = a + bx was studied in six subjects during cycling on an ergometer at 60 or 100 rpm at work loads below 80% of VO2max. Three subjects had an average of 78% ST fibers (ST group) and the other subjects had an average of 76% FT fibers (FT group). There was no difference between the two groups in delta efficiency at 60 rpm, but at 100 rpm the efficiency of the ST group was significantly lower than that of the FT group (19.6 vs. 28.8%, P less than 0.01). In the ST group respiratory exchange ratio (R) was higher at 100 rpm than at 60 rpm, but the FT group had similar R values at both pedal revolution rates. The most important finding was the reduced efficiency when pedaling frequency was increased from 60 to 100 rpm in the ST group (23.3 to 19.6%). Predominant use of ST fibers at rapid pedal rates may require a substantial increase in energy expenditure.

Adult↗

PubMed1977

In vitro studies of skeletal muscle membranes. Effects of denervation on the macromolecular components of cation transport in red and white skeletal muscle.

The effects of denervation on the macromolecular components of active monovalent cation transport in skeletal muscle have been studied using purified sarcolemma membranes. A comparison of membrane activities of fast-twitch, slow-twitch, and mixed-fiber muscles was made to determine what role, if any, the motor nerve has in regulating this important aspect of muscle metabolism. A dramatic increase in the basal sarcolemmal Mg++ ATPase activity (three- to fourfold) was found for both major muscle types. An increase in the ouabain-inhibitable (Na+ + K+)-stimulated enzyme was also found, but the effect was substantially less (1.5- to twofold). [3H]-ouabain binding, as an index of glycoside receptor sites, also increased (two- to threefold) midway in the course of denervation. On the other hand, the phosphorylated intermediate activity, a functional component of the transport system, clearly decreased over the same time course and remained below control values for the remainder of the course. This resulted in a two- to threefold increase in the turnover number, suggesting that active transport of cations should increase dramatically with denervation. The membrane protein patterns on SDS gels were less obvious than the changes observed in the functional components. The major effects appeared after only one week and seemed to be restricted to high molecular weight membrane proteins, especially in the 100,000 to 250,000 daltons range. This effect was more prominent in slow-twitch membranes with an apparent semiquantitative decrease in stain at 240,000 daltons. In gels of membranes from fast-twitch muscles a decreased stain in the range of 100,000 to 110,000 daltons occurred, and this became more obvious with longer periods of denervation. The results suggest that considerable influence on the macromolecular components of active cation transport in skeletal muscle is exerted by the motor nerve. No appreciable difference was found in this effect when the two major types of skeletal muscle, fast-twitch and slow-twitch, were compared, suggesting that motor nerve regulation of this membrane property is qualitatively the same.

Adenosine Triphosphatases↗

PubMedDate not supplied

Experimental autoimmune myasthenia gravis in the rat: a preliminary report.

In chronic experimental myasthenia gravis (EAMG) in rat, the decrement of electrical and mechanical responses evoked by maximal repetitive (3-167/sec) stimuli to the nerve was greater in the slow-twitch soleus (SOL) than in the fast-twitch extensor digitorum longus (EDL) muscle. Excitation-contraction coupling was impaired in moderate to severe EAMG, as evidenced by a diminished staircase phenomenon and by diminished posttetanic potentiation (PTP) of twitch tension in two EDLs. The only morphologic abnormality observed was an increase in length of the endplates in the EDLs of those animals that had had an acute phase of EAMG. The latter had more than a 90% reduction in the amplitude of the action potential and in the twitch tension of the EDL when stimuli were applied to the nerve. Stimuli applied directly to the muscle evoked a tetanic tension that was one-third of normal. The staircase and PTP were normal. Necrosis occurred in the endplate and in the adjacent segment of muscle fiber; outside the endplate region, the muscle fiber was normal.

Animals↗

PubMedDate not supplied

Morphology and physiology of skeletal muscle in aging rodents.

Aging in the rodent is accompanied by a progressive loss of skeletal muscle fibers. The muscle twitch also becomes slower, probably as a result of fiber-type conversion from "fast-twitch" to "slow-twitch." The loss of muscle fibers precedes signs of obvious weakness and appears to involve the loss of entire functioning motor units. In the mouse, this loss of motor units correlated with a loss of axons from the innervating nerve trunks.

Adenosine Triphosphatases↗

PubMed1977

Muscle fiber types in women athletes and non-athletes.

Muscle biopsies were obtained from the vastus lateralis muscle of 5 female collegiate field hockey players and 5 untrained female students. The fibers were classified histochemically as fast-twitch-oxidative-glycolytic (FOG), fast-twitch-glycolytic (FG) and slow-twitch-oxidative (SO). The fibers were found to be similar to those of males in distribution and histochemical properties, but were smaller. In the women athletes all 3 fiber types were larger than the respective fibers in the controls. Also, the athletes had a much higher percentage of oxidative fibers (SO + FOG), 83% vs. 46%. A direct relationship between fiber size and oxidative activity was observed in fast-twitch fibers, whereas the reverse was found in slow-twitch fibers.

Adenosine Triphosphatases↗

PubMed1976

Force-velocity characteristics for calcium-activated mammalian slow-twitch and fast-twitch skeletal fibers from the guinea pig.

Twitch fiber bundles from a slow (soleus) and a fast (extensor digitorum longus) mammalian muscle after mild chemical treatment were activated with calcium and relaxed in calcium-free solution. Like the electrically activated whole muscles, the force-velocity relationship was such that, at each relative load, the steady speed of shortening for the fast fibers was about two times greater than that for the slow twitch fibers. The duration of pre-steady motion in the two types of fibers was the same. The data provide direct evidence that the difference in the shortening characteristics of the two types of fibers is due to differences in their cross-bridge properties.

Animals↗

PubMed1979

Torque-velocity relationships and muscle fiber composition in elite female athletes.

The relationship between the predominance of fast and slow muscle fibers of the vastus lateralis and "in vivo" torque velocity properties in 22 female athletes was studied. Fiber types were classified according to the histochemical myofibrillar adenosine triphosphatase technique at a basic pH. Maximal extensor troques were recorded at 30 degrees from full extension at four selected velocities. While results confirm earlier reports on muscle fiber type and performance, an additional finding was that as knee extension velocities increased from 0 to 95 degrees/s angle specific extensor torque production did not decline as seen in in vitro muscle preparations. The difference in extensor torque between 0 and 96 degrees/s appeared far more critical than the differences observed between 96 and 288 degrees/s. Significant differences in torque were seen at 96, 192, and 288 degrees/s in thos with greater than 50% and less than 50% slow-twitch fibers. When expressed per kilogram of body weight the subjects with greater than 50% fast-twitch fiber produced the greatest torque at 192 degrees/s. These results suggest that the velocity at which torque begins to decline in vivo is related to the proportion of slow-twitch fibers in the vastus lateralismuscle.

Adolescent↗