scholarly journals Further Study of the Electrical and Mechanical Responses of Slow Fibers in Cat Extraocular Muscles

1967 ◽  
Vol 50 (9) ◽  
pp. 2289-2300 ◽  
Author(s):  
G. Pilar
Keyword(s):  
Neuromuscular Junctions ◽  
Muscle Fibers ◽  
Slow Muscle ◽  
Oblique Muscle ◽  
Mechanical Responses ◽  
Electrical Pulses ◽  
Slow Type ◽  
Types Of Muscle Fibers

Electrical and mechanical responses have been obtained in situ and in vitro from the superior oblique muscle stimulated by single and repetitive electrical pulses, applied to the trochlear nerve. Two different types of muscle fibers are described, the twitch and the slow. The slow type is characterized electrically by the presence of junctional potentials, which have reversal potentials between -10 and -20 mv, and do not show propagated responses or spikes, during nerve stimulation. When the slow muscle fibers are repetitively stimulated in situ, a prolonged contraction is maintained during stimulation. At the time, the recorded electrical activity is produced locally, at the level of the neuromuscular junctions of the slow fibers. These results indicate that the contractile mechanism of the slow muscle fibers is activated locally and segmentally.

Effect of depolarization by potassium proprionate on synaptic vesicle diameter and distribution of the snake motor endplate

1989 ◽  
Vol 47 ◽  
pp. 946-947
Author(s):  
Gregory Hendricks ◽  
Lisa Coniglio ◽  
Ian Marshall ◽  
Tim Searl ◽  
Rodney Parsons
Keyword(s):  
Synaptic Vesicles ◽  
Neuromuscular Junctions ◽  
Muscle Fibers ◽  
Average Diameter ◽  
Uranyl Acetate ◽  
Release Agent ◽  
High K ◽  
Microscope Slides ◽  
Whole Mounts

The morphological effects of elevated potassium (K+) at the neuromuscular junction of garter snake twitch muscle fibers were examined in vitro. Elevated K+ depolarizes the motor neuron terminals and causes quantal release of acetylcholine. It has been shown in amphibians that prolonged (30-60 min) depolarization with high K+ depletes terminals of synaptic vesicles ; but causes no change in the average diameter of the vesicles. In the snake, however, we have shown previously that miniature endplate currents (MEPCs) are present at high frequency even after 1-2 hours of exposure to high K+ . This indicates that in the snake, synaptic vesicles are not totally depleted by depolarization with high K+. In this study, we examined the effect of depolarization with high K+ on the distribution and diameter of synaptic vesicles.Intercostal muscle preparations were exposed for 15 minutes to Ringer's + solution containing either a control (1.2mM) or high (70mM) concentration of K+ Preparations were fixed immediately in 1% glutaraldehyde for 15 minutes and washed with Millonig's buffer. The whole mount muscle preparations were then fixed for 1 h in 2.5% glutaraldehyde in 0.1 M phosphate buffer, pH 7.2; rinsed three times in fresh buffer and post-fixed in 2% OsO4 in the same buffer for 30 min, rinsed in fresh buffer and dehydrated in a graded ethanol series to 100% and then transferred into a 2% solution of uranyl acetate for 20 min to en-block stain the whole mounts. The preps were then transferred back to 100% ethanol to complete the dehydration and embedded in a mixture of Embed 812/Araldite 502 (Hard) between two microscope slides that had been precoated with Formen- Trennmittel Liquid Release Agent and polymerized overnight at 70°C.The whole mounts were then removed from the microscope slides and examined on a compound light microscope where the neuromuscular junctions on the twitch muscle fibers could be identified, marked and cut out of the preps. These pieces of the whole mounts were then remounted into a slot on the end of a pre-cast Embed-Araldite block with a drop of fresh resin and polymerized.

Carbonic anhydrase III, an early mesodermal marker, is expressed in embryonic mouse skeletal muscle and notochord

Development ◽  
1991 ◽  
Vol 111 (1) ◽  
pp. 233-244 ◽  
Author(s):  
G.E. Lyons ◽  
M.E. Buckingham ◽  
S. Tweedie ◽  
Y.H. Edwards
Keyword(s):  
Skeletal Muscle ◽  
Carbonic Anhydrase ◽  
Post Partum ◽  
Muscle Fibers ◽  
Slow Muscle ◽  
Mrna Levels ◽  
Embryonic Mouse ◽  
Carbonic Anhydrase Iii

Carbonic anhydrase III (CAIII) is an abundant soluble protein in adult mammalian slow twitch skeletal muscle fibers. It is thought to be an early marker for myogenesis based upon its high level of expression in myoblasts in vitro prior to fusion. Using in situ hybridization, we have studied the in vivo distribution of CAIII gene transcripts in mouse embryos and fetuses from 7.25 days to 17.5 days post coitum (p.c.). CAIII mRNAs are first detected in the myotomes of somites between 9.5 and 10.5 days p.c. (20–30 somites). At 15.5 days p.c., CAIII begins to be restricted to developing slow muscle fibers. By two weeks post partum (p.p.), CAIII mRNAs are detected mainly in slow muscle fibers. CAIII transcripts are detected at an earlier stage (7.25 days p.c.) in the developing notochord. CAIII is expressed at a much higher level in the notochord than it is in developing skeletal muscle. As the notochord forms the nucleus pulposus in fetal mice, CAIII mRNA levels remain very high. Expression of CAIII in the notochord is of interest in the context of skeletal myogenesis because the notochord is thought to play an important role in somite formation. In addition to the notochord, CAIII transcripts are detected prenatally in several other non-muscle tissues: in cells of the choroid plexus, endocardial cushion and ureter, and in adipocytes.

Action of pyridine-2-aldoxime methochloride (PAM) on neuromuscular transmission in vitro and in vivo

1968 ◽  
Vol 46 (5) ◽  
pp. 757-764 ◽  
Author(s):  
G. Robert Goyer
Keyword(s):  
Neuromuscular Transmission ◽  
Muscle Fibers ◽  
Toxic Action ◽  
Myoneural Junction ◽  
Twitch Potentiation ◽  
Nerve Muscle ◽  
Higher Doses

The action of pyridine-2-aldoxime methochloride (PAM) was evaluated on nerve–muscle preparations in vitro and in situ. On the isolated diaphragm of the rat, PAM shows a d-tubocurarine-like effect at concentrations higher than 6 mM. No facilitating effects were observed with lower concentrations, even when the acetylcholinesterases were inhibited to an important extent. However, the biphasic actions of PAM could be demonstrated with nerve–muscle preparations of the rat and rabbit in situ: lower concentrations produced fasciculations and twitch potentiation whereas a depressing d-tubocurarine-like effect was obtained with higher doses. The decrease in the amplitude of contraction appears to be related to an action at the myoneural junction rather than a direct toxic action on the muscle fibers themselves.

In vivo imaging of GLUT4 translocationThis paper is one of a selection of papers published in this Special Issue, entitled 14th International Biochemistry of Exercise Conference – Muscles as Molecular and Metabolic Machines, and has undergone the Journal’s usual peer review process.

2009 ◽  
Vol 34 (3) ◽  
pp. 420-423 ◽  
Author(s):  
Hans P.M.M. Lauritzen
Keyword(s):  
Skeletal Muscle ◽  
Insulin Signalling ◽  
Muscle Fibers ◽  
Muscle Contractions ◽  
Confocal Imaging ◽  
Glut4 Translocation ◽  
Channel Network ◽  
T Tubules

In skeletal muscle, both insulin and muscle contractions mediate translocation of glucose transporter GLUT4 to the plasma membrane proper, the sarcolemma, and the specialized membrane channel network, the transverse (t)-tubules. Despite the fact that skeletal muscle glucose uptake plays a major role in normal conditions, in insulin resistance, and type II diabetes, the details of GLUT4 translocation and the intracellular signalling involved have not been fully described. A main reason is that the majority of experiments have been carried out in muscle cultures in vitro. In vitro cultured muscle is not fully differentiated and, therefore, diverges from real muscle, in that it has lower expression of GLUT4, an underdeveloped or nonexistent t-tubule network, and a reduced or nonexistent response to insulin. Thus, experiments carried out in cultured muscle cell systems might give misleading results on how GLUT4 translocation and the signalling involved takes place. To address this problem, a confocal imaging technique has been developed that allows delineation of the spartial and spatial distribution of GFP-tagged GLUT4 (GLUT4-GFP) translocation in living muscle fibers in situ in anesthetized mice. The effects of stimuli with insulin or in situ muscle contractions in fully differentiated muscle fibers can now be studied before, during, and after applying stimuli. Initial analysis of insulin-stimulated GLUT4-GFP translocation showed a delay in maximal translocation between the sarcolemma and t-tubules. Corresponding to the delay, we found that fluorescent tagged insulin reaches the sarcolemma first and then, with a delay, diffuses into the t-tubule system, enabling interaction with local insulin receptors and, in turn, triggering local insulin signalling and local GLUT4 translocation. In parallel, we showed that the majority of GLUT4 depot vesicles do not move long distances but are depleted locally in the sarcolemma or t-tubule regions. Analysis of GLUT4 translocation in insulin-resistant muscle showed that, primarily, GLUT4 recruitment in the t-tubule region is affected. We have now analysed the kinetics of contraction-mediated GLUT4 translocation and reinternalization, as well as dilineated some of the key signalling points involved in these processes.

In vitro formation of neuromuscular junctions between adult Rana muscle fibres and embryonic Xenopus neurons

1987 ◽  
Vol 230 (1261) ◽  
pp. 425-441 ◽  
Keyword(s):  
Neuromuscular Junctions ◽  
Rana Temporaria ◽  
Amplitude Distribution ◽  
Mean Amplitude ◽  
Muscle Fibres ◽  
Electron Microscopical ◽  
Early Regeneration ◽  
Miniature Endplate Potentials

Adult muscle fibres of the frog Rana temporaria were cultured with neurons from embryos of the frog Xenopus laevis . Electron microscopical and electro-physiological examination of the cultures showed that hetero-specific ( Xenopus- Rana ) neuromuscular junctions were formed in vitro . Nerve processes, without any Schwann cell covering, made contacts anywhere along a muscle fibre, and the junctions resembled those seen during early regeneration of neuromuscular synapses in situ . Functional contacts, as inferred by the presence of spontaneous miniature endplate potentials, or currents, were more common if the muscle fibres were denervated prior to culturing with neurons. Miniature endplate currents (m. e. p. cs) had a skewed amplitude distribution, with many small events lost in the recording noise, and their mean amplitude was much smaller than that of m. e. p. cs in the original lumbricalis muscle. The time constant of decay of m. e. p. cs in the hetero-specific junctions formed in vitro was several times longer than the decay of m. e. p. cs in the original muscle. Analysis of membrane current noise elicited by ionophoretically applied acetylcholine (ACh) suggests that the slower decay of m. e. p. cs in the junctions formed in vitro is due to a prolonged lifetime of the channels opened by ACh and to repetitive activation of ACh-receptors, which becomes possible because of a comparative lack of cholinesterase in the junctions.

scholarly journals Ectopic Overexpression of Porcine Myh1 Increased in Slow Muscle Fibers and Enhanced Endurance Exercise in Transgenic Mice

2018 ◽  
Vol 19 (10) ◽  
pp. 2959 ◽  
Author(s):  
Jin Ahn ◽  
Dong-Hwan Kim ◽  
Hee-Bok Park ◽  
Sang-Hyun Han ◽  
Seongsoo Hwang ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Transgenic Mice ◽  
Muscle Fibers ◽  
Slow Muscle ◽  
Physical Endurance ◽  
Fiber Types ◽  
Muscle Composition ◽  
Transition Mechanism ◽  
Muscle Tissues ◽  
Slow Type

Myosin heavy chain (MyHC) isoforms consist of Myh7, Myh2, Myh1, and Myh4, which are expressed in skeletal muscle tissues during postnatal development. These genes influence the contraction–relaxation activity in skeletal muscles and are involved in determining muscle composition such as the proportion of fast-to-slow and/or slow-to-fast fiber types. Among them, Myh1 is associated with skeletal muscle contraction and is involved in both slow-to-fast and fast-to-slow transition. However, the muscle transition mechanism is not well understood. For this study, we first produced porcine Myh1 transgenic (TG) mice to study whether the ectopic expressed porcine Myh1 gene had any effects on muscle composition, especially on slow-type muscle components. Our results showed that the factors associated with slow muscles, such as Myh7, Myoglobin, Troponin (slow-type units), and cytochrome C, were highly expressed in the quadriceps muscles of Myh1 transgenic mice. Furthermore, the ectopic porcine MYH1 protein was located only in the slow-type muscle fibers of the quadriceps muscles in Myh1 transgenic mice. In physical endurance tests, Myh1 transgenic mice ran longer and further on a treadmill than wild-type (WT) mice. These data fully supported our hypothesis that Myh1 is associated with slow muscle composition, with overexpression of Myh1 in muscle tissues possibly being a new key in modulating muscle fiber types. Our study provides a better understanding of muscle composition metabolism, physical mobility, and genetic factors in muscle fatigue.

Correlated Studies of Cellular Interactions Using TEM, Freeze Etching, and SEM

1974 ◽  
Vol 32 ◽  
pp. 320-321
Author(s):  
J. P. Revel
Keyword(s):  
Developmental Stages ◽  
Three Dimensional ◽  
Cell Movement ◽  
Cellular Interactions ◽  
Serial Sections ◽  
Cell Sheets ◽  
Freeze Etching ◽  
Early Developmental

Movement of individual cells or of cell sheets and complex patterns of folding play a prominent role in the early developmental stages of the embryo. Our understanding of these processes is based on three- dimensional reconstructions laboriously prepared from serial sections, and from autoradiographic and other studies. Many concepts have also evolved from extrapolation of investigations of cell movement carried out in vitro. The scanning electron microscope now allows us to examine some of these events in situ. It is possible to prepare dissections of embryos and even of tissues of adult animals which reveal existing relationships between various structures more readily than used to be possible vithout an SEM.

In vitro and in vivo polysaccharides assembly: ultrastructural and cytochemical study of growing plant cell wall components.

1978 ◽  
Vol 36 (2) ◽  
pp. 434-435
Author(s):  
D. Reis ◽  
B. Vian ◽  
J. C. Roland
Keyword(s):  
Cell Wall ◽  
Self Assembly ◽  
Plant Cell Wall ◽  
Higher Plants ◽  
Three Dimensional ◽  
Cytochemical Study ◽  
Wall Components

Wall morphogenesis in higher plants is a problem still open to controversy. Until now the possibility of a transmembrane control and the involvement of microtubules were mostly envisaged. Self-assembly processes have been observed in the case of walls of Chlamydomonas and bacteria. Spontaneous gelling interactions between xanthan and galactomannan from Ceratonia have been analyzed very recently. The present work provides indications that some processes of spontaneous aggregation could occur in higher plants during the formation and expansion of cell wall.Observations were performed on hypocotyl of mung bean (Phaseolus aureus) for which growth characteristics and wall composition have been previously defined.In situ, the walls of actively growing cells (primary walls) show an ordered three-dimensional organization (fig. 1). The wall is typically polylamellate with multifibrillar layers alternately transverse and longitudinal. Between these layers intermediate strata exist in which the orientation of microfibrils progressively rotates. Thus a progressive change in the morphogenetic activity occurs.

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