Showing papers on "Skeletal muscle published in 1970"
TL;DR: The repeated contractions which can be observed in skinned fibres in appropriate concentrations of caffeine, Ca2+ and chelating agent suggest that calcium release is a regenerative process in which calcium itself causes the release of calcium from the reticulum.
Abstract: The repeated contractions which can be observed in skinned fibres in appropriate concentrations of caffeine, Ca2+ and chelating agent suggest that calcium release is a regenerative process in which calcium itself causes the release of calcium from the reticulum.
751 citations
TL;DR: It is suggested that the Differences in the low-molecular-weight components of myosin from different types of muscle are a consequence of differences in the isoenzyme composition of the myosins.
Abstract: 1. The low-molecular-weight components of myosin freshly prepared by the standard procedure from adult rabbit skeletal muscle migrated as four main bands Ml1, Ml2, Ml3 and Ml4 on polyacrylamide-gel electrophoresis in 8m-urea. 2. The number of bands increased on storage. This change was accelerated by increasing the temperature and pH. 3. None of the bands had electrophoretic mobilities identical with those of the well-characterized proteins of the myofibril or with the sarcoplasmic proteins. 4. By varying the ionic conditions and concentration of muscle mince used for the initial extraction it was possible to change the relative proportions of the two electrophoretic bands of intermediate mobility, Ml2 and Ml3. 5. The four-band picture similar to that obtained with rabbit was observed with myosin isolated from skeletal muscle of the rat, mouse, hamster, pigeon and chicken. 6. Rabbit cardiac myosin gave only two bands on electrophoresis. Myosin from rabbit red muscle gave a pattern intermediate between cardiac and white-skeletal-muscle myosin, i.e. the two fastest bands were present in decreased relative amounts. 7. It is suggested that the differences in the low-molecular-weight components of myosin from different types of muscle are a consequence of differences in the isoenzyme composition of the myosins.
653 citations
TL;DR: It was suggested that the muscle nuclei which take up thymidine 3H and undergo mitosis are not true muscleuclei but belong to "muscle satellite cells", which was concluded that satellite cell nuclei are eaily distinguished from true Muscle nuclei in the electron microscope.
Abstract: Much is known about the early stages of muscle development-the proliferation of myoblasts, their fusion into myotubes, and the transformation of myotubes into young muscle fibers . However, the mode of growth of muscle in the young animal remains obscure . It is known that muscle growth is extensive (e .g . in the chicken the pectoralis muscle enlarges from 0.7 g at hatching to 300 g in the adult) and is mainly the result of hypertrophy of the fibers (1), with little, if any, increase in their number (2) . Moreover, it is generally assumed that, unlike what happens in most other tissues, there is no division of the nuclei and, consequently, no increase in their number (3) . This view is supported by experiments showing that, while myoblasts can divide at early stages of development, they lose this ability once they have been incorporated into myotubes (4) . Furthermore, during muscle regeneration following injury, myoblasts appear which take up thymidine-'H, indicating their ability to divide, whereas the nuclei of muscle fibers do not (5) . Hence the prevalent opinion has been that new nuclei are not produced in skeletal muscle fibers during growth . This view was questioned when DNA determinations revealed a considerable increase in the number of fiber nuclei during growth in rats (6) and chickens (1), and mitotic figures were observed within the muscle fibers of growing rats (7) . Furthermore, after an injection of thymidine3H, radioautography revealed labeled nuclei within the confines of the basement membrane of muscle fibers (7, 8). In the hope of reconciling these apparently conflicting observations, it was suggested that the muscle nuclei which take up thymidine 3H and undergo mitosis are not true muscle nuclei but belong to \"muscle satellite cells\" (7). Such cells, which had been observed only in the electron microscope (9), consist of a single nucleus surrounded by scanty cytoplasm and are located between the basement membrane and the plasmalemma of the fibers, whereas true muscle nuclei are within the plasmalemma . Since satellite cell nuclei are eaily distinguished from true muscle nuclei in the electron microscope, it was decided to examine radioautographs in this instrument following thymidine 3H injection . Six male rats aged 17 days and weighing 25-30 g were given a single injection of 25-60 )uCi of thymidine 3H; g body weight and sacrificed at intervals varying from I to 72 hr later . The tibialis anterior muscle was fixed by immersion in glutaraldehyde paraformaldehyde (10), postfixed in osmium tetroxide, and embedded in Epon . Thin (silver to gold) sections were prepared for radioautography in the electron microscope with Ilford L4 emulsion (11-13) and poststained with lead citrate (14) . Electron microscopy revealed the existence of two types of nuclei within the basement membrane of the fiber . The nuclei of the first type (85-90% of the total) are in direct contact with the myofibril-containing cytoplasm ; they are the true muscle nuclei. The nuclei of the second type are surrounded by a small amount of cytoplasm, which is separated from the myofibril-containing cytoplasm by an intercellular space; these are the satellite cell nuclei ; they are usually smaller and darker than true muscle nuclei . In radioautographs obtained I hr after injection of thymidine 3H, approximately 3% of the nuclei within the basement membrane were labeled . These invariably belonged to satellite cells (Fig. 1) . Not one of the true muscle nuclei was labeled at that time. The results were similar at 6 and 10 hr after injection (Table I) . It was, therefore, concluded that satellite cell nuclei, but not true muscle nuclei, were able to synthesize DNA . Moreover, since it is known that DNA synthesis precedes mitosis (8), it may be concluded that the mitotic figures previously observed in the muscle fibers of growing rats (7) must belong to satellite cells . This conclusion is in accord with a recent report that, after colchicine treatment of 30-g rats, arrested mitoses of the nuclei of satellite cells, but not of true muscle nuclei, may be observed (15) . By 24 hr, a few true muscle nuclei were also labeled (Table I). At 48 hr, the labeling frequency of true muscle nuclei was increased, and by 72
303 citations
TL;DR: This report summarizes the current analytical techniques and conceptualizations, illustrated by examples from the present and previous investigations, and investigates whether there is selective or nonselective involvement of muscle fiber types in each human and animal condition studied.
Abstract: DURING the past few years, our studies of the histochemical changes of skeletal muscle in human neuromuscular diseases and experimental animal models have gradually led to the development of an analytical approach which places major emphasis upon determining whether there is selective or nonselective involvement of muscle fiber types in each human and animal condition studied. Such determinations provide a new approach to the pathogenesis and etiology of the neuromuscular disorders. This report summarizes our current analytical techniques and conceptualizations, illustrated by examples from our present and previous investigations. Background Data and Hypotheses.— Histochemistry of fresh frozen muscle biopsy specimens from humans and animals demonstrates different degrees of enzyme activity in different fibers within the same muscle. The distinct histochemical characteristics of a given muscle fiber (which is a single, long, multinucleated cell) are maintained throughout its length, making it possible to obtain histochemical profiles of the individual
259 citations
TL;DR: In recent experiments it has become apparent that there are marked differences in the rate at which abnormalities develop in soleus and gastrocnemius and these differences can be correlated closely with the histological characteristics of these muscles which allow their muscle fibres to be designated as 'fast' or 'slow'.
Abstract: Botulinum toxin causes paralysis of skeletal muscle by preventing the release of acetylcholine at motor nerve terminals (Burgen, Dickens, and Zatman, 1949). It is known that, when a sub-lethal quantity of toxin is injected directly into muscles of experimental animals, paralysis and atrophy of those muscles develop and persist for a long time (Guyton and MacDonald, 1947; Jirmanova, Sobotkova, Thesleff, and Zelena, 1964; Duchen and Strich, 1967, 1968). A remarkable overgrowth of motor nerve fibres occurs while the muscles are paralysed and atrophied (Duchen and Strich 1968) and changes in the localization of cholinesterase activity develop. After some weeks muscular function recovers, the nerve growth ceases and then regresses, and the motor innervation of the muscle and the distribution of cholinesterase become reorganized. The pattern of innervation and the morphology of subneural apparatuses remain abnormal permanently. Although the histological investigations of Duchen and Strich (1968) showed that abnormalities develop in the innervation and in the morphology of the subneuralapparatuses, the exact relationship between the changes in cholinesterase localization and the sprouting of motor nerve fibres was not determined. This paper presents the result of recent histological studies of the effects of botulinum toxin on skeletal muscle of the mouse in which the relationship of the motor nerve growth to the development of abnormalities in cholinesterase and its localization was examined. In recent experiments it has become apparent that there are marked differences in the rate at which abnormalities develop in soleus and gastrocnemius and these differences can be correlated closely with the histological characteristics of these muscles which allow their muscle fibres to be designated as 'fast' or 'slow'. The differences in the histological changes induced by botulinum toxin in the various muscles are described in this paper. These observations have been briefly presented in a preliminary communication (Duchen, 1969).
238 citations
204 citations
TL;DR: The technique of extracellular space tracing with horseradish peroxidase is adapted for labeling the transverse tubular system (T system) in rat heart and in atrial muscle the following two types of cells are found: those cells with a well-developed T system in which the tubular diameter is quite uniform and the orientation predominantly longitudinal and, (b) cells with no T system, but with aWell-developed L system.
Abstract: The technique of extracellular space tracing with horseradish peroxidase is adapted for labeling the transverse tubular system (T system) in rat heart. In rat ventricular muscle the T system shows extensive branching and remarkable tortuosity. The T system can only be defined operationally, since it does not display specific morphological features throughout its entire structure. Owing to branching of the T system, a sizable proportion of the apposition between the T system and L system (or closed system) occurs at the level of longitudinal branches of the T system and is not restricted to the Z line region. The regions of apposition between the T system and L system are analyzed in rat ventricular muscle and skeletal muscle (diaphragm) and compared with the intercellular tight junctions (nexuses) of heart muscle by the use of a photometric method. The over-all thickness of the nexus is significantly smaller than that of T-L junctions in both cardiac and skeletal muscles. The thickness of the membranes of the T and L systems are not significantly different in the two muscles, but the gap between both membranes is larger in the heart. In atrial muscle the following two types of cells are found: (a) those cells with a well-developed T system in which the tubular diameter is quite uniform and the orientation predominantly longitudinal and, (b) cells with no T system, but with a well-developed L system. Atrial cells possessing a T system are richly provided with specific granules and show little micropinocytotic activity, whereas cells devoid of T system show intense micropinocytotic activity and few specific granules. The possible functional implications of these findings are discussed.
204 citations
TL;DR: A purified rabbit skeletal muscle adenosine 3',5'-monophosphate (cyclic AMP)-stimulated protein kinase enhanced lipolytic activity in adipose tissue homogenates and it is inferred that this effect is due to the phosphorylation and activation of a lipase in a system analogous to that involved in the activation of muscle glycogen phosphorylase.
201 citations
TL;DR: It appears that in cardiac muscle an inotropic shift of Vmax of the contractile element cannot be distinguished from a shift due to change in fiber length, thus invalidating it as an index of contractility.
Abstract: The use of maximum velocity of shortening (V max ) as an index of contractility has been based on the assumption that V max of muscle fibers is equivalent to V max of the contractile element. It is shown here that such equivalence applies to the two-element model of skeletal muscle but not to three-element models of cardiac muscle. Analysis of published data in terms of the Voigt and Maxwell three-element models shows that the V max of the contractile element, unlike that of the muscle fibers, is not independent of fiber length but increases at least 50% for a 25% increase of fiber length. Moreover, V max of the contractile element is seen to be even more highly dependent on fiber length when correction is made for the nonuniform contribution of levels of active state to the force-velocity curves giving rise to V max of the contractile element. It appears that in cardiac muscle an inotropic shift of V max of the contractile element cannot be distinguished from a shift due to change in fiber length, thus invalidating it as an index of contractility.
157 citations
TL;DR: Postnuclear supernates from homogenates of skeletal muscle from rats subjected to starvation and injections of Triton WR-1339 and dextran + corticosterone were fractionated, indicating the presence of two groups of lysosome-like particles from muscle cells.
Abstract: Postnuclear supernates from homogenates of skeletal muscle from rats subjected to starvation, injections of Triton WR-1339, dextran-500, and dextran + corticosterone were fractionated by means of rate and isopycnic zonal centrifugation in sucrose—0.02 M KCl gradients. Zonal fractions were analyzed for protein, RNA, cytochrome oxidase, and up to six acid hydrolases. The results indicate the presence of two groups of lysosome-like particles. One group contributes approximately 95% of the cathepsin D and acid phosphatase activity and 75% of the acid ribonuclease, β-glucuronidase, and arylsulfatase activity in muscle. It is characterized by a modal equilibrium density of 1.18 that is decreased by starvation, but is not shifted by dextran-500 or Triton WR-1339. The second group has a higher proportion of acid ribonuclease, β-glucuronidase, and arylsulftase; the equilibrium density can be shifted by dextran-500 and Triton WR-1339. It is suggested that this group of lysosomes is derived from macrophages and other connective tissue cells, whereas the former group represents lysosome-like particles from muscle cells.
157 citations
TL;DR: Since the constrictor effect of DHE seems confined mainly to the capacitance vessels, the drug may have beneficial effects in circulatory disorders characterized by impaired venomotor regulation.
Abstract: 1. A comparative quantitative study of the effects of dihydroergotamine (DHE) and noradrenaline (NA) on the precapillary and postcapillary resistance vessels, the precapillary ‘sphincters’, and the capacitance vessels was performed in a skeletal muscle and a skin region in healthy humans and in patients with orthostatic symptoms; further, the vascular effects of the drugs were analysed in muscle, skin, intestine and kidney in cats before and after sympathectomy. 2. The two drugs evoked a similar pattern of response in the cutaneous vascular bed, i.e. they both constricted resistance and capacitance vessels, increased the ratio of pre-/post-capillary resistance, but did not significantly influence precapillary sphincters. The reactions were similar in skeletal muscle for NA and also for DHE, with the important exception that the latter drug usually elicited a moderate dilator response in the muscle resistance vessels. 3. The average constrictor responses of the capacitance vessels were significantly larger for DHE than NA in skin and also in muscle despite the fact that DHE did not much affect the resistance vessels in muscle. 4. The effects of DHE on the intestinal and renal vascular circuits in the cat were comparatively small. 5. Since the constrictor effect of DHE seems confined mainly to the capacitance vessels, the drug may have beneficial effects in circulatory disorders characterized by impaired venomotor regulation.
TL;DR: Muscle protein turnover, in particular myofibrillar, was shown to be very sensitive to dietary protein and/or calorie deficiency and therefore importance of muscle protein metabolism in the economy of the whole animal is discussed.
Abstract: 1. Rates of synthesis and catabolism of liver and muscle sarcoplasmic and myofibrillar protein have been measured in young control, starved and protein (deprived) rats using [ 14 C]Na 2 CO 3 to label protein. 2. Half-lives for synthesis of 1·35, 2·8 and 7·2 days for liver, sarcoplasmic and myofibrillar proteins respectively were obtained, whilst half-lives for catabolism were 1·55, 3·6 and 15·6 days in each case in the control animals. 3. The protein free diet for 3 days caused a small decrease in the rate of synthesis of liver and muscle proteins. The catabolic rate of liver protein was increased by 20% whilst there was a smaller increase in the catabolic rate of myofibrillar proteins. 4. Starvation for 3 days caused a 20% reduction in the rate of liver protein synthesis whilst there were greater reductions in muscle protein synthesis. The catabolic rate of liver protein was only slightly increased whereas there was a 75% increase in the rate of myofibrillar protein breakdown. 5. The total amount of protein synthesis and catabolism in liver and the two muscle protein fractions over the first 3 days of the three regimes were calculated. Muscle protein turnover, in particular myofibrillar, was shown to be very sensitive to dietary protein and/or calorie deficiency. 6. These results are discussed in terms of the mobility and therefore importance of muscle protein metabolism in the economy of the whole animal.
Journal Article•
TL;DR: It is postulated that aspartate and glutamate labelled by the injection of [ 14 C]CO = 3 are only reutilized to a very small extent and therefore afford the means by which the rates of protein synthesis and catabolism in skeletal muscle can be measured with reasonable accuracy.
Abstract: 1. The turnover of rat skeletal muscle protein was studied using [ 75 Se]selenomethionine, [6- 14 C]arginine and [ 14 C]Na 2 CO 3 to label protein. 2. In rats labelled with both [ 75 Se]selenomethionine and [ 14 C]Na 2 CO 3 the 14 C activity of mixed skeletal muscle protein fell rapidly with a half-life of 6·0 days for the specific activity and 10·5 days for the total activity. There was no loss of 75 Se activity from muscle protein during the 12 days of the experiment. 3. Following the injection of [6- 14 C]arginine both sarcoplasmic and myofibrillar proteins continued to incorporate label for 6 days after which time the label was lost fairly rapidly. 4. Following the injection of [ 14 C]Na 2 CO 3 muscle protein was maximally labelled by 6 h, at which time specific activity of the free amino acids had fallen to a very low level. Aspartate and glutamate in particular had lost over 99% of their maximum activity by this time in comparison to arginine which was still highly labelled after 24 h. 5. 14 C activity was lost more rapidly from aspartate and glutamate isolated from sarcoplasmic and myofibrillar protein than from the other labelled amino acids. The half-lives of the two protein fractions were 3·9 and 7·2 days from the specific activity curves and 6·0 and 19·0 days from the total activity curves. 6. The differences between the half lives of muscle proteins labelled with different amino acids are discussed in terms of the effects of reutilization of the labelled amino acid used. It is postulated that aspartate and glutamate labelled by the injection of [ 14 C]CO = 3 are only reutilized to a very small extent and therefore afford the means by which the rates of protein synthesis and catabolism in skeletal muscle can be measured with reasonable accuracy.
TL;DR: The analysis of the frequency dependence of the impedance of skeletal muscle fibres showed that fibres “detubulated” by the glycerol method had a low frequency capacity of 2.1 µF/cm2 as compared with 5–12 µF /cm2 in normal fibres.
Abstract: THE relatively large electrical capacity of skeletal muscle fibres1,2 is generally attributed to the transverse tubular system which ramifies over the cross-section of the fibre and enlarges the effective area of the surface. From an analysis of the frequency dependence of the impedance, Falk and Fatt3 assigned a capacity of 2.6 µF/cm2 to the surface membrane and 4.1 µF/cm2 to the contribution of the tubules. Gage and Eisenberg4 showed that fibres “detubulated” by the glycerol method had a low frequency capacity of 2.1 µF/cm2 as compared with 5–12 µF/cm2 in normal fibres.
TL;DR: The data suggest that the enzyme in resting muscle is partially or completely inhibited; when ADP accumulates in muscle it removes the inhibition by nucleoside triphosphates, Pi and creatine phosphate and the enzyme results activated.
TL;DR: The hypothesis based on previous evidences that the main circulatory changes in physical training occur in the circulation of the skeletal muscle is supported.
Abstract: Six weeks' physical training of seven healthy subjects was followed by a mean decrease of exercise muscle blood flow (ml./100 g/min) from 32·7 to 22·6 and an increase of succinic dehydrogenase activity ( V O2 μl./g/min) from 33·0 to 47·4 in vastus lateralis muscle. Estimated maximal aerobic power ( V O2 max.) increased by 30%. These results support the hypothesis based on previous evidences that the main circulatory changes in physical training occur in the circulation of the skeletal muscle.
TL;DR: In this article, histochemical studies of affected muscle in two patients with Cushing's syndrome are described and indicate that the grossly visible wasting can be accounted for by a diminution in diameter of practically all muscle fibers, with atrophy being more prominent in the type II (high in myofibrillar ATPase, high in most mitochondrial oxidative enzymes) fibers.
Abstract: CUSHING'S syndrome or therapy with any of the glucocorticoids may cause proximal muscular weakness.1,2Muscle wasting is usually apparent clinically. Occasional fibers undergoing degeneration and scattered atrophic fibers have been described in muscle biopsy specimens.1,3,4In this paper, histochemical studies of affected muscle in two patients with Cushing's syndrome are described and indicate that the grossly visible wasting can be accounted for by a diminution in diameter of practically all muscle fibers, with atrophy being more prominent in the type II (high in myofibrillar adenosine triphosphatase [ATPase] and phosphorylase) than in the type I (low in myofibrillar ATPase, high in most mitochondrial oxidative enzymes) fibers.5There was no evidence of a myopathic process in the usual sense of necrosis, phagocytosis, cellular infiltrates, or endomysial connective tissue proliferation. The potassium content of muscle was diminished. Report of Cases CASE1.—This 67-year-old woman was confined to bed during
TL;DR: Results from cross-reinnervation techniques are interpreted as indicating that regulation of gene expression is one of the “trophic” functions of the vertebrate neuron.
TL;DR: Despite an increase in cyclic 3',5'-AMP concentration and kinase activity in the muscle, epinephrine caused no measurable increase in phosphate incorporation into the enzyme, suggesting difficulties in detecting small changes in the degree of phosphorylation during activation in vivo of the kinase.
Journal Article•
TL;DR: Several observations are reported that suggest that the enzymes from muscle and kidney are not identical, and growth hormone, either in vivo or in vitro, did not affect the measured glutamine synthetase activity of tissue extracts.
Abstract: 1. Glutamine synthetase activity has been determined in extracts of rat cardiac and skeletal muscle and kidney, after treatment to ensure that the rate of synthesis was proportional to time of incubation and to amount of extract added. The activity was measured by two methods, with hydroxylamine as substrate. 2. No activity was detected in rat heart extract by either method. The activity in skeletal muscle was of the order of 20μmol of glutamylhydroxamate synthesized/h per g of tissue under optimum conditions. The activity in kidney extracts was 180μmol/h per g of tissue when measured as ferric hydroxamate. 3. The activity in both skeletal-muscle and kidney extracts was inhibited by Pi. The inhibition is competitive for the muscle enzyme, with a Ki of 12mm. For the kidney enzyme the inhibition is non-competitive, and less marked. Possible enzyme mechanisms that would lead to these types of inhibition are discussed. 4. Several observations are reported that suggest that the enzymes from muscle and kidney are not identical. 5. Growth hormone, either in vivo or in vitro, did not affect the measured glutamine synthetase activity of tissue extracts.
TL;DR: The chapter outlines the characteristics of this crucial transition period in developing muscle tissue and inquires the relationship of protein accumulation to protein synthesis expressed as amino acid incorporation.
Abstract: Publisher Summary This chapter hopes to promote progress toward an understanding of muscle development by attempting to integrate the results of the different lines of research An approximate schedule of the successive steps in the determination of mesodermal tissue that leads to the development of presumptive muscle cells in the limb buds of the chick is elaborated The chapter outlines the characteristics of this crucial transition period in developing muscle tissue It begins with the frustrating problem of the first appearance of cell-specific proteins Two general difficulties in the analysis of developmental processes are encountered The first of these pertains to the definition of what is meant by specific cell proteins Perhaps more critical is the second difficulty—defining what is meant by “the first appearance” of a cell-specific protein The appearance and increase in myosin in skeletal muscle is used as the standard indicator The overall activity of the transcriptional and translational system is measured as incorporation of amino acids into proteins The chapter inquires the relationship of protein accumulation to protein synthesis expressed as amino acid incorporation
TL;DR: The effects of the amines on the cat soleus muscle appears to be analogous to that causing enhancement of physiological tremor in man, which suggests that skeletal muscle tremor may be an occasional unwanted side effect of the use of these bronchodilators.
Abstract: 1. (-)-Isoprenaline, salbutamol, orciprenaline and quinterenol injected intravenously decreased the tension and degree of fusion of incomplete tetanic contractions of the soleus muscle of the anaesthetized cat.2. Under the most sensitive conditions, the smallest effective dose of (-)-isoprenaline was of the order of 0.01 mug/kg intravenously. Salbutamol was usually 6-10 times, orciprenaline 20-30 times and quinterenol about 35 times less potent than isoprenaline. The effects of salbutamol were about 1.6 times, of orciprenaline about 1.8 times and of quinterenol more than 20 times as long lasting as those of (-)-isoprenaline.3. The effects of the sympathomimetic amines were blocked by propranolol, H56/28, H35/25 and butoxamine but not by ICI 50172. The combined results with agonists and antagonists indicate that the receptors involved can be classified as of the beta(2) type.4. The effect of the amines on the cat soleus muscle appears to be analogous to that causing enhancement of physiological tremor in man, which suggests that skeletal muscle tremor may be an occasional unwanted side effect of the use of these bronchodilators.
TL;DR: Selective stimulation of ventral cord or ventral root can evoke widespread synchronized contractions of large numbers of fibers in the muscle expiant, demonstrating abundant formation of functional neuromuscular junctions between the coupled tissues.
Abstract: Functional neuromuscular junctions formin vitro between spatially separated explants of fetal mammalian spinal cord and fetal skeletal muscle, even across species lines (rat and mouse). Differentiation and innervation occur when the muscle explant is oriented toward the ventral edge of the spinal cord cross-section, in the path of ventral-root nerve fibers. Arrival of these neurites enhances muscle development. This trophic influence is particularly apparent when cortisone is included in the nutrient fluid. Cross-striations begin to form toward the end of the first week of coupling, and acetylcholinesterase-positive loci appear by three weeks. In cultures maintained for 5–11 weeks, the more differentiated motor endplate structures show characteristic subneural infoldings, increased soleplate sarcoplasm, and terminal Schwann cells. Myelinated ventral-root fibers can be seen to bridge the gap between the cord and muscle explants, and to arborize and terminate on muscle fibers. Selective stimulation of ventral cord or ventral root can evoke widespread synchronized contractions of large numbers of fibers in the muscle expiant, demonstrating abundant formation of functional neuromuscular junctions between the coupled tissues.
TL;DR: The 3-methylhistidine content of myosin varies according to muscle type as discussed by the authors, it is highest in white skeletal muscle and lower values are obtained from red skeletal and smooth muscle.
Abstract: 1. The 3-methylhistidine content of myosin varies according to muscle type. It is highest in myosin from white skeletal muscle and lower values are obtained from myosin of red skeletal and smooth muscle. 2. The 3-methylhistidine content of actin was similar in all of the types of muscle from which it was isolated. 3. The 3-methylhistidine of rabbit actin is localized in a single tryptic peptide that was readily modified during fractionation procedures. 4. Photo-oxidation studies indicated that the 3-methylhistidine residues are not essential for adeonsine triphosphatase and actin-combining activities of myosin. 5. During photooxidation G-actin lost completely the ability to polymerize to the F form before all the 3-methylhistidine was destroyed.
TL;DR: The creatine-P kinase of the fragmented sarcoplasmic reticulum preparation represents approximately 1% of the total activity in muscle and may be significant as a localized source of ATP for calcium transport processes during muscle relaxation.