Immature Muscle Cells Research Articles

Effect of chronic electrical stimulation at low frequency on the passive membrane properties of muscle fibers from dystrophic mice

It has been reported that chronic electrical stimulation at low frequency applied to dystrophic muscles has a beneficial effect. In this study, the effect of this treatment on the passive membrane properties of muscle fibers from dystrophic mice was followed. Cable properties were assessed by the two-microelectrodes DC method and spacial decay analysis. Earlier results showing a decrease in resting potential, an increase in input resistance and in specific membrane resistance in muscle fibers from dystrophic mice were confirmed. In addition, the specific membrane capacitance of these muscle fibers was found to be lower than normal. This suggests that the membrane properties of fibers from dystrophic muscles are similar to those of immature muscle fibers. Muscle fibers from dystrophic animals that were stimulated for 2 to 4 weeks had membrane properties similar to those from normal muscles. This indicates that electrical stimulation at low frequency for 2 to 4 weeks restores membrane properties of dystrophic muscle fibers to normal and we suggest that an appropriate pattern of stimulation induces the maturation of dystrophic muscle fibers.

Myotoxic activity of the crude venom and the principal neurotoxin, taipoxin, of the Australian taipan, Oxyuranus scutellatus.

1 The crude venom of the Australian taipan. Oxyuranus scutellatus and its principal neurotoxin, taipoxin, were injected into the anterolateral aspect of one hind limb of the rat. 2 The effects of the venom and toxin on the morphology and physiology on the underlying soleus muscles were examined. 3 Both the crude venom and the toxin caused necrosis and degeneration of the muscle. Damage to the peripheral muscle fibres could be seen at the light microscopic level as early as 3 h after injection of the toxic compounds. 4 The necrotic response was accompanied by an infiltration of phagocytic cells and an extensive oedema. The wet weight of the damaged muscles was almost doubled by 6 h. 5 In individual muscle fibres, necrosis was associated with the disruption of the plasma membrane and the disorganization of the myofibrils. The basal lamina of the muscle fibres was left intact. 6 Denervated mammalian muscles and innervated avian muscles were also destroyed by tiapoxin, but immature avian muscle growing in tissue culture was resistant. 7 Of the 3 subunits of taipoxin, only the basic alpha-taipoxin was itself myotoxic. However, its potency was enhanced by the presence of the acid gamma subunit. The role of the neutral beta-subunit is unclear. 8 The period of necrosis and degeneration lasted for approximately 48 h, after which the muscle fibres began to regenerate. Regeneration took place within the surviving basal lamina, with the formation of myotubes by three days, and small, immature muscle fibres by five days. Regeneration was virtually complete by 21 days.

Morphological changes of myofibril in the carcinogenetic course of 20-methylcholanthrene-induced rhabdomyosarcoma.

In this study 20-methylcholanthrene (MC) was embedded in skeletal muscle tissue of mice. The resulting morphological changes were observed by light and electron microscope until the occurrence of rhabdomyosarcoma. The injected region of the muscle tissue in which MC was embedded went through three stages: destruction and degeneration, repair and appearance of atypical cells. The morphologic figures of the myofibrils seen in the skeletal muscle cell during destruction and degeneration were similar to nonspecific. The muscle tissue then regenerated in the same manner as seen during experimentally induced muscle tissue regeneration in both humans and animals. Abnormal mitotic figures were found 60 to 70 days after the injection of MC. Immature muscle cells, with tuft-formed myofibrils present, underwent abnormal mitosis in which one of the nuclei divided. The rhabdomyosarcoma cells produced by this abnormal mitosis began to appear in the lesion 70 days after the initial embedding of MC. The rhabdomyosarcoma cells in the induced tumor formed undifferentiated myofibrils in various degrees of maturation, and were therefore considered to play a part in the abnormal myofibrillar formation.

Is Kugelberg-Welander spinal muscular atrophy a fetal defect?

Twelve children who had developed Kugelberg-Welander (K-W) spinal muscular atrophy (SMA) before the age of six years were investigated. Electrophysiological, histochemical, ultrastructural, and biochemical studies demonstrated features of immature muscle fibers suggesting a fetal defect as in the Werdnig-Hoffmann (W-H) form of SMA. Comparison with known patterns of human myogenesis and of experimental denervation of immature muscle suggested that the defect in K-W SMA probably takes place in fetal life at a stage later than in W-H SMA. In contrast to W-H SMA, a considerable percentage of mature fibers of normal structure and diameter were present. The immature fibers impair the normal development of muscle cells by preventing the increase in number of mature fibers and causing an overloading of the normal fibers with consequent hypertrophy and eventually destructive changes. This is the pattern in K-W disease that distinguishes the juvenile form of SMA from W-H disease.

I. Ultrastructural Characteristics of Developing Human Muscle

Muscle cells of 25 humans fetuses 7, 9, 10, 14, 17, 20, and 24 weeks old were examined by electron microscopy to determine the structural characteristics of developing muscle. Three structurally different levels of maturation of muscle cells, the primitive myotube, the mature myotube, and the immature muscle fibers, have been observed in the process of human ontogenesis. The sequence of morphological changes and the timing of transformation of one form of fetal muscle into a more mature form are presented.

Development of membrane conductance of chick skeletal muscle in culture. II. Effect of aminopyridines.

The effects of 4-aminopyridine and 3,4-diaminopyridine on membrane parameters during differentiation of embryonic chick skeletal muscle in culture have been studied. Both agents caused depolarization of fibres at all stages of development. In older cultures (day 6 onward), membrane conductance was suppressed by 0.1 mS cm-2. The addition of a maximal blocking concentration of tetraethylammonium to aminopyridine-treated fibres caused no further change in membrane conductance. In older cultures, it is concluded that the aminopyridines block resting potassium conductance. However in young fibres (day 3 to day 5), the aminopyridines caused an increase in membrane conductance. It is postulated that the aminopyridines increase membrane conductance to sodium or calcium or a combination of the two ions in immature muscle fibres.

Further observations on the pathological responses of rat skeletal muscle to toxins isolated from the venom of the Australian tiger snake, Notechis scutatus scutatus.

1. Some aspects of the response of mammalian skeletal muscle following the injection of purified toxins from the venom of the Australian tiger snake, Notechis scutatus scutatus, are described. 2. The toxins used were notexin, notechis II-5, notechis II-1 and a modified form of notexin (PBP-notexin). They were injected into the dorso-lateral aspect of one himd limb so that the soleus muscle would be exposed to the toxins. 3. Within 1 h after the injection of notexin, the soleus muscles were oedematous and by 3--6 h, polymorphonuclear leucocytes had entered the interstitial spaces. The invasion of necrotic muscle fibers was extensive by this time. Muscle spindles appeared relatively unaffected by the toxin. 4. The muscle regenerated via myoblasts at 2--3 days to myotubes at 3--5 days, immature muscle fibers at 7--14 days and fully differentiated muscle fibers by 21--28 days. Even after 6 months, however, the nuclei of many muscle fibres remained in a central position. 5. A second component of Australian tiger snake venom was also found to be myotoxic. It was slightly less potent than notexin, but caused qualitatively similar damage to that caused by notexin. It was identified as notechis II-5. A third fraction, notechis II-1, was found to be inactive. 6. Notexin could be neutralized by incubation with tiger snake antivenene; the simultaneous injection of antivenene with notexin did not afford complete protection against muscle damage.

Muscle lesions in embryos and chicks on the day of hatching.

Histopathological studies were carried out on skeletal muscles of 1, 723 individuals consisting of embryos, and abnormal and normal chicks which had been collected on the days of hatching during the same year. Muscle lesions were readily found in 360 (21%) of the specimens at low-power magnification microscopy. Muscle fibers in the lesions showed mainly focal swelling, focal rarefaction with a lack of myofibrils and sarcoplasm, and the appearance of basophilic substance. Some of the lesions were associated with mild reactive changes in the interstitial connective tissue. Based on the findings of rarefied areas in the affected muscle fibers, a pyesumption was made that these muscle lesions might have occurred in immature muscle fibers and be regarded as a hypoplastic change.

Adaptive changes in developing rat skeletal muscle in response to functional overload

The histochemical profile of rat skeletal muscles can be modified in response to the increased functional overload induced by incapacitation of synergistic muscles. We have investigated the effect of synergist elimination in rats of different age, in order to compare the relative plasticity of immature versus mature muscle fibers and the role of peripheral factors on fiber type differentiation. The chronic effects of increased functional overload were studied in the rat extensor digitorum longus (EDL) and extensor hallucis longus (EHL) muscles after extirpation of the synergistic tibialis anterior muscle. After tibialectomy at birth there was a marked increase in succinate dehydrogenase activity in overloaded muscles: the typical “white” or mitochondria-poor fibers, which constitute about 40% of the fiber population in the control muscles, were altogether absent in the hypertrophic EDL and EHL. However, the activity of another mitochondrial enzyme, α-glycerophosphate dehydrogenase, was unchanged or, in some cases, even slightly decreased in most fibers of the overloaded muscles. The proportion of fibers with low myosin ATPase activity increased from 4% of the total fiber population in the control EDL to 10–15% in the hypertrophic muscle, and comparable changes were seen in EHL. Tibialectomy performed 1 or 2 months after birth, by contrast, induced rather limited or, in the case of EDL, almost negligible changes in the histochemical profile both with respect to mitochondrial oxidative enzymes and myosin ATPase. The findings show that the adaptive response of skeletal muscle to synergist elimination is markedly influenced by the degree of maturity of the muscles at the time the overload is imposed.

Some effects of local anesthetic agents on skeletal muscle

The gracilis anticus and posticus muscles of albino rats were exposed to a number of common local anesthetic agents. In general, clinically used concentrations of most agents appeared to be specifically destructive of skeletal muscle. Results also suggest that higher concentrations are more generally histotoxic. The sequence of muscle changes after one drug (2% lidocaine) was followed over an extensive time period. Muscle regeneration from single myoblasts was found to be rapid and complete by 2 weeks. Preferential destruction of red- or white-type muscle fibers was observed after many of the agents. The drug effects are discussed relative to the characteristics of mature and immature muscle fibers and the physical properties and biological activities of the local anesthetics.

Development of apposed sarcoplasmic reticulum at the T system and sarcolemma and the change in orientation of triads in rat skeletal muscle

The SR network in immature skeletal muscle fibers forms a lacelike network of diverging and converging tubules oriented both longitudinally and transversely around the fibril. The network is irregularly oriented and does not appear to be differentiated at various fibril striation levels as in adult fibers. Triads in immature fibers are fewer in number and are oriented predominantly longitudinally while in the adult they are numerous and encircle the fibril transversely at the A-I junction. Densely staining material within SR apposed at the T or sarcolemma has been shown to be structural in nature. Periodic bridges traverse a space approximately 100 Å wide between apposed membranes. A density coextensive with the apposed SR limiting membrane is located near the inside surface of the membrane. Densities appear to form connections between the coextensive density and the apposed SR limiting membrane. Additional dense structures are located in the expanded SR segment between the coextensive density and the unapposed SR membrane. Observations on fetal and very young rats suggest that the earliest differentiation of structures within apposed SR is dependent upon close apposition of undifferentiated SR network tubule segments at the T or sarcolemma. The coextensive density is seen only in apposed SR showing periodic bridges traversing the space between apposed membranes. The formation of bridges between apposed membranes would therefore appear to be prerequisite to differentiation of the coextensive density and its connections to the apposed SR limiting membrane. It is suggested that expansion of the apposed SR tubule in a plane perpendicular to apposition accommodates additional structures between the coextensive density and the unapposed SR limiting membrane. Structures showing expansion characteristics of apposed SR are never found unless the SR is indeed apposed at the T or the sarcolemma. Observations on fibers from fetal and newborn to 35-day rats have shown that the predominantly longitudinally oriented triads of immature fibers change orientation. The change from predominantly longitudinally to transversely oriented triads is complete in the larger fibers from animals 10 to 15 days postnatal. It is of interest to note that this change in orientation corresponds to the observed marked decrease in E-C latency.

An Electron-Microscopic Study of the Muscles of Rabbits Subjected to Chronic Anaemia during Foetal Life

The fine structure of the red and white muscle cells of the newborn rabbit after chronic anaemia during foetal life has been studied. The changes in the structure both red and white muscle were similar and consisted in the swelling and vacuolisation of the mitochondria and sarcoplasmic reticulum as well as in the destruction of miofibrils. The most characteristic feature was the presence of numerous immature muscle cells in the stage of myotube and myoblast and the absence of differences in the structure between the red and white muscles. This observation showed that chronic anaemia in foetal life seems to be one of the exogenous factors causing modifications in the muscle development.

Glycogen synthetase, phosphorylase, and glycogen content of developing rhesus muscle.

Extract: Total glycogen synthetase and syntheatse I (glucose 6-PO4 indendependent) and phosphorylase and phosphorylase a activites determined in muscle from fetal,neonatal, infant, and adult rhesus monkeys (Macaca mulatta) and correlated with glycogen concentrations. On the basis of nitrogen content, glycogen levels in fetuses in the 55- to 65-day series where higher than those in fetuses in the 100-day series, but similar to those in the fetuses near term (table I). Both glycogen synthetase and phosphorylase activities where demonstrated histochemically in the immature muscle fibers from fetuses at 55, 62, and 65 days of gestation. Total synthetase activity (assayed with 10 mM glucose 6-PO4) was demonstrated quantitatively at 78 days of gestation; this activity was highest at term (table II). No synthetase I activity could be found in the 78- and 90-day series (table II); hence, it is suggested that in fetal muscle, synthetase Dis responsible for the levels of glycogen present early in gestation. No correlatin between the glycogen content and the percentage of synthetase I present coulf be found in fetal muscle (fig.1). Total phosphorylase, lowest at 78 days of gestation, increased almost 10-fold by term (table II). No singnificant phosphorylase a activity could be demonstrated at 78 days; however, by 90–100 days, phosphorylase a activity was present and remained at about the same level (2–7%) thereafter. It is concluded that the enzymes for glycogen formation and degradation are present in immature muscle fibers of the rhesus fetus as early as the first third of gestation (55 days). The ratio of totao synthetase to phosphorylase activites facors lycogen deposition in the younger fetus (78–125 days) and glycongen breakdown in the fetus at term. Speculation: In adult animals, control of muscle glycogen metabolism depends greatly on hormonal activity; insulin promotes glycogen formation by increasing synthetase D to I conversion, and epinephrine causes glycogenolysis by promoting phosphorylase a formation while depressing synthetase activity. The role of hormonal control of glycogen metabolism may be less critical in fetal muscle than it is in adult muscle. If synthetase D is the active from of the enzyme in glycogen formation in fetal muscle, it would appear that at the cellular level, insulin is a less important regulator of glycogen synthesis than a metabolite control.

Clasmatothenesis, a new type of amitotic nuclear division in striated muscle cells of insects.

A new type of amitotic nuclear division in differentiating striated muscle cells of insects (Dermatobia cyaniventris Macquart, Polybia scutellaris White, Photinus fuscus and Acromyrmex lundi) is described. It consists of a process of multiple fragmentation of a single chromatic cord, a sort of giant longitudinal macronucleus which extends almost the entire length of the immature muscle cell. We have designated this interesting nuclear structure as polykaryonema and this amitotic nuclear division process as clasmatothenesis.

Leiomyosarcoma of the Uterus: With Case Report

According to Dannreuther, leiomyosarcoma implies sarcomatous change in a tumor composed chiefly of relatively histologically mature but physiologically immature unstriped muscle cells. Other terms designating the same condition, depending upon the pathologist’s interpretation, are leio-blastoma; myosarcoma; myoma malignum; and highly cellular myoma.