Hindlimb muscle fiber types in two frogs (Rana catesbeiana and Litoria caerulea) with different locomotor behaviors: histochemical and enzymatic comparison

To test how differences in locomotor behaviors may be reflected in muscle fiber-type diversity within anurans, a comparison of hindlimb muscles between the powerful terrestrial hopper, Rana catesbeiana, and the tree frog, Litoria caerulea, was done. One postural muscle (tibialis posticus, TP) and one primary hopping muscle (plantaris longus, PL), were characterized to identify muscle fiber types using standard histochemical methods. In addition, spectophotometric analysis of activity levels of the oxidative enzyme citrate synthase (CS) and the glycolytic enzyme lactate dehydrogenase (LDH) were done in each muscle. In spite of presumed differences in behavior between the species, we found no significant differences in the proportions of the identified fiber types when the muscles were compared across species. In addition, there were no significant differences in the proportions of the different fiber types between the postural versus phasic muscles within species. Within Rana, the postural muscle (TP) had greater oxidative capacity (as measured by CS activity) than did the phasic muscle (PL). Both muscles had equivalent LDH activities. Within Litoria, PL and TP did not differ in either LDH or CS activities. Both PL and TP of Litoria had less LDH activity and greater CS activity than their homologs in Rana. Thus, in spite of the uniform populations of fiber types between muscles and species, the metabolic diversity based on enzyme activity is consistent with behavioral differences between the species. These results suggest that the range of functional diversity within fiber types may be very broad in anurans, and histochemical fiber typing alone is not a clear indicator of their metabolic or functional properties.     

Chest wall motion during epidural anesthesia in dogs

To determine the relative contribution of rib cage and abdominal muscles to expiratory muscle activity during quiet breathing, we used lumbar epidural anesthesia in six pentobarbital sodium-anesthetized dogs lying supine to paralyze the abdominal muscles while leaving rib cage muscle motor function substantially intact. A high-speed X-ray scanner (Dynamic Spatial Reconstructor) provided three-dimensional images of the thorax. The contribution of expiratory muscle activity to tidal breathing was assessed by a comparison of chest wall configuration during relaxed apnea with that at end expiration. We found that expiratory muscle activity was responsible for approximately half of the changes in thoracic volume during inspiration. Paralysis of the abdominal muscles had little effect on the pattern of breathing, including the contribution of expiratory muscle activity to tidal breathing, in most dogs. We conclude that, although there is consistent phasic expiratory electrical activity in both the rib cage and the abdominal muscles of pentobarbital-anesthetized dogs lying supine, the muscles of the rib cage are mechanically the most important expiratory muscles during quiet breathing.     

Muscle weights and succinic dehydrogenase distribution in the hind limb musculature of two rodents (Thryonomys gregorianus and Pedetes capensis) with different locomotory habits

The hind limb muscles of the spring hare (Pedetes capensis) were found to be relatively heavier than the hind limb muscles of the cane rat (Thryonomys gregorianus). The distribution of succine dehydrogenase activity was investigated in four of these muscles (m. gluteus superficialis, m.semimembranosus, m. biceps femoris and m.rectus femoris) from both animals. It was found that the spring hare had a higher proportion of low-activity fibres in all four muscles than the cane rat. All muscle fibre types were also smaller in diameter in the spring hare than the cane rat. These results are discussed in relation to the different locomotry habits of the two animals.     

Some properties of transport ATPases in functionally different muscles]

The properties of Ca-transporting system in sarcoplasmic reticulum membranes in fast and slow frog muscles as well as some properties of sarcolemma Na, K-ATPase of the same object were investigated. The rate of Ca2+ uptake, Ca-ATPase activity and Ca/ATP ratio for the reticulum of fast muscle demonstrated higher values than those for the reticulum of slow muscle. The rate of Ca2+ accumulation by the fragments of the rectus reticulum and Ca/ATP ratio were found to decrease under the influence of acetylcholine (0.05-5 mM). The transport system of the sartorius reticulum was found to be less sensitive to acetylcholine. The peak activity of Na, K-ATPase in femoral muscles of the frog occurred at 80 mM NaCl and 60 mM KCl, whereas in the rectus abdominal muscle it equalled 100 mM NaCl and 40 mM KCl. Thus, Na, K-ATPase activity in the slow muscle was predominantly higher than that in the mixed (femoral) muscles. If the sarcolemma preparations of the muscles of both types the inhibitory effect of acetylcholine on Na; K-ATPase was registered. The enzyme of slow muscles exhibited higher sensibility to acetylcholine.     

Appearance of high-molecular-weight acetylcholinesterase in aneural muscle developing in vivo

Acetylcholinesterase was studied in the superior oblique muscle of the duck embryo during the course of in vivo development. Normally developing, paralyzed, and uninnervated muscles were studied using velocity sedimentation for separation of various forms and biochemical determination of enzyme activity, and light and electron microscopy for histochemical and cytochemical localization of enzyme. Results indicate that neither muscle activity nor contact by the motor neurons is essential for the appearance of high-molecular-weight form of acetylcholinesterase on muscle cells developing in vivo. Acetylcholinesterase activity per muscle was considerably lower in the paralyzed and aneural muscles than the normal muscle. The absolute loss of acetylcholinesterase parallels loss of muscle protein in paralyzed and aneural muscles and may be secondary. Paralysis or absence of innervation had no significant effect on the specific activity of acetylcholinesterase.     

Acetazolamide-sensitive and resistant carbonic anhydrase activity in rat and rabbit skeletal muscles of different fiber type composition

1. Acetazolamide (ACET)-resistant and -sensitive carbonic anhydrase (CA) activity was measured in post-mitochondrial supernatants from the soleus (SOL), deep vastus lateralis (DVL) and superficial vastus lateralis (SVL) muscles of rats and rabbits. 2. The relative total CA activity in the three muscles of both species can be summarized as SOL greater than DVL greater than SVL. 3. ACET-resistant CA activity was found in the SOL and DVL muscles of both species whereas a low level of ACET-sensitive CA activity was detected in the SVL muscle. 4. ACET-sensitive CA activity was also found in sarcoplasmic reticulum preparations from rat and rabbit SOL muscles.     

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.     

Long-term activity in upper- and lower-limb muscles of humans.

Despite limited data on humans, previous studies suggest that there is an association between the duration of daily muscle activity and the proportion of type I muscle fibers. We quantified the activity of limb muscles in healthy men and women during normal use and compared these measurements with published reports on fiber-type proportions. Seven men (age range = 21-28 yr) and seven women (age range = 18-26 yr) participated in two 10-h recording sessions. Electromyogram (EMG) activity of four muscles in nondominant upper (first dorsal interosseus and biceps brachii) and lower limbs (vastus medialis and vastus lateralis) was recorded with surface electrodes. Hand and arm muscles were active for 18% of the recording time, whereas leg muscles were active for only 10% of the recording time. On average, upper-limb muscles were activated 67% more often than lower-limb muscles. When lower-limb muscles were activated, however, the mean amplitude of each burst was greater in leg muscles [18 and 17% maximum voluntary contraction (MVC)] compared with hand (8% MVC) and arm (6% MVC) muscles. Temporal association in activity between pairs of muscles was high for the two lower-limb muscles (r2 = 0.7) and relatively weak for the two upper-limb muscles (r2 = 0.09). Long-term muscle activity was only different between men and women for the biceps brachii muscle. We found no relation between duration of muscle activity in 10-h recordings and the reported values of type I fibers in men and women.     

Glycerol kinase activities in muscles from vertebrates and invertebrates

1. Glycerol kinase (EC 2.7.1.30) activity was measured in crude extracts of skeletal muscles by a radiochemical method. The properties of the enzyme from a number of different muscles are very similar to those of the enzyme from rat liver. Glycerol kinase from locust flight muscle was inhibited competitively by l-3-glycerophosphate with a K(i) of 4.0x10(-4)m. 2. The activity of glycerol kinase was measured in a variety of muscles from vertebrates and invertebrates in an attempt to explain the large variation in the activity of this enzyme in different muscles. 3. In vertebrates glycerol kinase activities were generally higher in red muscle than in white muscle; the highest activities (approx. 0.2mumole/min./g. fresh wt.) were found in the red breast muscle of some birds (e.g. pigeon, duck, blue tit) whereas the activities in the white breast muscle of the pheasant and domestic fowl were very low (approx. 0.02mumole/min./g.). 4. On the basis of glycerol kinase activities, muscles from insects can be classified into three groups: muscles that have a low enzyme activity, i.e. <0.3mumole/min./g. (leg muscles of all insects studied and the flight muscles of cockroaches and the tsetse fly); muscles that have an intermediate enzyme activity, i.e. 0.3-1.5mumoles/min./g. (e.g. locusts, cockchafers, moths, water-bugs); and muscles that have a high enzyme activity, i.e. >1.5mumoles/min./g. (e.g. bees, wasps, some blowflies). 5. The function of glycerol kinase in vertebrate and insect muscles that possess a low or intermediate activity is considered to be the removal of glycerol that is produced from lipolysis of triglyceride or diglyceride by the muscle. Therefore in these muscles the activity of glycerol kinase is related to the metabolism of fat, which is used to support sustained muscular activity. A possible regulatory role of glycerol kinase in the initiation of triglyceride or diglyceride lipolysis is discussed. 6. The function of glycerol kinase in the insect muscles that possess a high activity of the enzyme is considered to be related to the high rates of glycolysis that these muscles can perform. The oxidation of extramitochondrial NADH, and therefore the maintenance of glycolysis, is dependent on the functioning of the glycerophosphate cycle; if at any stage of flight (e.g. at the start) the rate of mitochondrial oxidation of l-3-glycerophosphate was less than the activity of the extramitochondrial glycerophosphate dehydrogenase, this compound would accumulate, inhibit the latter enzyme and inhibit glycolysis. It is suggested that such excessive accumulation of l-3-glycerophosphate is prevented by hydrolysis of this compound to glycerol; the latter would have to be removed from the muscle when the accumulation of l-3-glycerophosphate had stopped, and this would explain the presence of glycerol kinase in these muscles and its inhibition by l-3-glycerophosphate.     

EMG modulation in anticipation of a possible trip during walking in young and older adults.

This study investigated whether changes in lower limb muscle activity occurred in anticipation of a possible perturbation in 11 young (mean age 27 years) and 11 older (mean age 68 years) adults. Altered muscle activity could affect tripping responses and consequently the ecological validity of experimental results of studies on tripping. It was hypothesized that anticipatory muscle activity would be present immediately after a trip, and decrease after several subsequent unperturbed (forewarned) walking trials. Electromyograms of lower limb muscles were measured in 3 conditions: during normal walking, during forewarned walking immediately after a trip, and during forewarned walking several trials after a trip had occurred. Small but statistically significant differences in averaged muscle activity over a stride were found among conditions. Young adults showed slightly increased activity immediately after tripping (co-contraction) in hamstrings, quadriceps and tibialis anterior muscles. This increased activity diminished after several unperturbed trials, although it did not return to the baseline activity levels during normal walking. In older adults, an increased muscle activity among conditions was only discerned in tibialis anterior and soleus muscles. This suggested that older adults prefer to avoid contact with the obstacle over joint stiffening. Yet, for both age-groups, the increases in muscle activity were very small when compared to tripping responses reported in the literature. Therefore, anticipatory effects are not expected to jeopardize the validity of experiments in which subjects are perturbed more than once.     

Dietary supplementation of old mice with flavonoid dihydroquercetin causes recovery of the mitochondrial enzyme activities in skeletal muscles

The effect of a potent antioxidant, flavonoid dihydroquercetin on the activity of three mitochondrial enzymes in mouse skeletal muscles has been investigated. An ability of this substance to restore the activity of mitochondrial enzymes in old animals was demonstrated. The activities of citrate synthase, NADHcoenzymeQ1-oxidoreductase (complex 1) and cytochromc-oxidase (complex 4) were assessed using spectro-photometric analysis in a quadriceps muscle homogenate. It was shown that the citrate synthase activity decreased moderately and the activities of complexes 1 and 4 in skeletal muscles dropped significantly in old mice. Supplementation of drink water with dihydroquercetin for a few weeks led to an increase of citrate synthase and complex 1 activity (P < 0.1) in muscles of old animals. Activity of complex 4 returned to the level found in the tissue of young mice. Maximal activity of citrate synthase and complex 1 was found in muscles of young mice. Sensitivity of NADH-coenzymeQ1-oxidoreductase to a specific inhibitor rotenone differed in all three groups of mice. Young and old mice exhibited about 95% and 84% of the total sensitivity, respectively, while in old mice receiving dihydroquercetin the sensitivity of complex 1 to the inhibitor increased up to 98%. The biochemical alterations entailed an increase in animals’ mobility as well as an improvement of fur and skin condition. Fatty acid composition of homogenate in muscle tissue of all three groups was also investigated. A reliable decline of the amount of linoleic acid and an increase in stearic and docosanoic acid contents as well as an increase of total amount of fatty acids in muscles of old mice were found. Statistically significant changes in fatty acid composition in muscles of old mice in the control group and in old mice receiving antioxidant were not observed.     

A study of skin deformation by optical coherence microscopy

The deformation of rat skin in response to cooling and stimulation of nerve fibers innervating the piloerector and vasoconstrictor muscles has been studied by optical coherence microscopy. It has been found that the deformation of skin upon cooling is due to the contraction of collagen fiber bundles rather than the smooth muscle of vessels or piloerectors.     

Shoulder reflexes.

Dynamic shoulder stability is dependent on muscular coordination and sensory inputs. In the shoulder, mechanoreceptors are found in the coracoacromial ligament, the rotator cuff tendons, the musculotendinous junctions of the rotator cuff and in the capsule. The number of receptors in the capsule is small compared to the number in the other shoulder structures. Proprioceptive information from numerous receptors in muscles and tendons is mediated via fast conducting nervefibers and probably contribute more to kinaestethic sensation than information from capsule and ligaments. Therefore it seems likely that the joint receptors have a more distinct role for the kinaestethic sense than muscle receptors. In cats a direct reflex from the afferents innervating the shoulder to the muscles around the shoulder has been presented. The reflex had an extremely short latency (2.7-3.1 ms). In man, a very long latency (300 ms) excitatory reflex has been found when nerves in the capsule were stimulated electrically during shoulder surgery. In addition, when the anterior-inferior capsule was excited in conscious humans with modest amplitude electrical stimuli during muscle activity, a strong inhibition was found with an average latency of 33 ms. Stimulation of the sensory nerves in the coracoacromial ligament has also been found to modify muscle activity strongly. Even though our understanding of the control of shoulder motion is incomplete, it is clear that sensory inputs can strongly modify muscle activity around the shoulder. This has implications for rehabilitation and shoulder surgery.     

Adaptation of rat skeletal muscle to creatine depletion: AMP deaminase and AMP deamination.

AMP deaminase catalyzes deamination of the AMP formed in contracting muscles to inosine 5'-monophosphate (IMP). Slow-twitch muscle has only approximately 30% as high a level of AMP deaminase activity as fast-twitch muscle in the rat, and rates of IMP formation during intense contractile activity are much lower in slow-twitch muscle. We found that feeding the creatine analogue beta-guanidinopropionic acid (beta-GPA) to rats, which results in creatine depletion, causes a large decrease in muscle AMP deaminase. This adaptation was used to evaluate the role of AMP deaminase activity level in accounting for differences in IMP production in slow-twitch and fast-twitch muscles. beta-GPA feeding for 3 wk lowered AMP deaminase activity in fast-twitch epitrochlearis muscle to a level similar to that found in the normal slow-twitch soleus muscle but had no effect on the magnitude of the increase in IMP in response to intense contractile activity. Despite a similar decrease in ATP in the normal soleus and the epitrochlearis from beta-GPA-fed rats, the increase in IMP was only approximately 30% as great in the soleus in response to intense contractile activity. These results demonstrate that the accumulation of less IMP in slow- compared with fast-twitch skeletal muscle during contractile activity is not due to the lower level of AMP deaminase in slow-twitch muscle.     

Cerebellar cortical activity during stretch of antagonist muscles

Single unit activity was recorded from the anterior lobe of the cerebellum during ramp and hold stretches of limb muscles in chloralose anesthetized cats. The activity of 95 "phasic" units showed a transient response during dynamic stretch of at least one muscle usually lasting for less than 350 ms following the stimulus onset. The activity of 59 phasic-tonic units was modified not only during dynamic stretch but also during the 1 s of maintained muscle length. All Purkinje cells, identified by their complex spikes, that responded to muscle stretch demonstrated exclusively phasic changes in discharge. Fourteen of 25 Purkinje cells (56%) responded to stretch of both antagonist muscles and these responses were always similar rather than reciprocal. From the 129 units without complex spikes, 70 demonstrated phasic discharge patterns whereas 59 had tonic responses. Seventy-five (59%) of these unidentified units revealed convergent responses to stretch of both antagonists, compared with 54 which responded to stretch of one muscle only. Of the unidentified units receiving convergent afferents from antagonist muscles, 62 (83%) had similar responses and only 13 (17%) had reciprocal reactions. There appeared to be no evidence that muscle afferents alone can induce reciprocal discharge patterns in Purkinje neurons of the cerebellar cortex. The firing frequency of some phasic-tonic units was correlated with both the velocity and amplitude of muscle stretch. No Purkinje cells were found with activity related to either velocity or amplitude of muscle stretch. One phasic and seven phasic-tonic unidentified units were activated at fixed latencies following trains of electrical stimulation applied to the thoracic spinal cord at frequencies exceeding 200 Hz, implying they were terminal portions of mossy fibers originating from direct spinocerebellar tracts. A few recordings of compound potentials were presumed to arise from the cerebellar glomeruli. The changing form of one of these potentials suggested that the glomerulus might be a site at which somatosensory peripheral information is modified by the cerebellar cortex.     

Functional dependence of single muscle receptors on muscle activity

In experiments on chloraloso-urethane anesthetized cats changes in spontaneous and induced spike activity of single muscle spindles and Golgi's receptors following a direct and/or indirect electrical stimulation of the muscle were studied. It was found that contractile activity of the plantar (phase) and heel (tonic) muscles decreased the spike activity of both muscle spindle and Golgi's receptors, the decrease in the phase muscle spindle activity being more considerable than in the tonic one.     

Acetylcholine receptor distribution on regenerating mammalian muscle fibers at sites of mature and developing nerve-muscle junctions

When rat soleus muscles fibers regenerated after notexin-induced damage, AChRs were present at high density on the surface of the new muscle fibers at the sites of the original NMJs, even if the intact motor axons were not present during regeneration. Some AChR molecules which were labelled with R-BgTx before notexin-induced damage persisted for some days at junctional sites after new muscle fibres had regenerated. During muscle fiber degeneration, components of the muscle fiber plasma membrane appeared to remain longer in the junctional region than elsewhere. When muscles on which new "ectopic" NMJs had been forming for at least 2 weeks were damaged, AChR clusters together with sites of high AChE activity were present 2 weeks later on the regenerated muscles in the region of new NMJ formation, even if the "foreign" nerve was not intact during the period of regeneration. If ectopic NMJs had been forming for only 4 days at the time of muscle and nerve damage, neither AChR clusters nor AChE activity were detected on the regenerated muscle fibers.     

Protein kinase C activity in rat skeletal muscle. Apparent relation to body weight and muscle growth

Protein kinase C (PKC) may be involved in growth regulation. In the present study the relationship between body weight, and thereby age, and the activity of PKC in muscle as well as in rapidly growing overloaded muscle were investigated. PKC activity in music was linearly inversely correlated to rat weight in both soleus (r = -0.59, P less than 0.05) and in plantaris (r = -0.74, P less than 0.01) muscles. During compensatory hypertrophy. PKC activity per muscle was maximally increased compared with the contralateral control muscles after 4 days in both soleus (126%) and in plantaris (105%) but had returned to basal levels by the 9th day. The data are in agreement with a role for PKC in muscle growth.     

Lipoprotein lipase activity in skeletal muscles of the rat: effects of denervation and tenotomy.

The effects of denervation, tenotomy, or tenotomy with simultaneous denervation on the activity of heparin-releasable and intracellular, residual lipoprotein lipase (LPL) and triacylglycerol (TG) content were examined in rat skeletal muscles. An influence of muscle electrostimulation on denervated and tenotomized muscles was also evaluated. Activity of both LPL fractions was decreased in denervated and/or tenotomized soleus and red portion of gastrocnemius muscles. It was accompanied by a slight elevation of the intracellular TG content. Electrostimulation increased activities of both fractions of LPL in red muscles from intact hindlimbs. In stimulated denervated muscles without or with simultaneous tenotomy, activity of two LPL fractions was also enhanced, but control values were reached only in denervated soleus muscle. Electrical stimulation had no pronounced effect on LPL activity in tenotomized muscles. In conclusion, denervation and/or tenotomy decreases LPL activity in red muscles, indicating reduction of the muscle potential to utilize circulating TG. Electrostimulation only partly restores the diminished LPL activity in denervated muscles, without any effect in tenotomized ones. Thus, to maintain LPL activity in resting muscle, intact innervation and tension are needed.