About the T-system in the myofibril-free sarcoplasm of the frog muscle fibre

Voigt, Tilman; Dauber, Wolfgang

doi:10.1016/j.tice.2004.03.004

Cited by 7 publications

(4 citation statements)

References 18 publications

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“…The presence of fluorescein dextran (Fig. 3) and lanthanum in electron microscopy studies (Voigt & Dauber, 2004) in these tubules indicates they are accessible from the transverse tubules.…”

Section: Resultsmentioning

confidence: 92%

“…The darkened elliptical region most probably represents the position of a nucleus. The tubules extending longitudinally from the pole of the nucleus into the myofibril‐free cytoplasmic space are occupied by Golgi apparatus and mitochondria (Voigt & Dauber, 2004). The presence of fluorescein dextran (Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Tubules were also observed in the myofibril‐free space, which presumably were at the poles of a nucleus within a high density of Golgi and mitochondria (Fig. 3; Voigt & Dauber, 2004). The architecture of the tubules in this region suggests a physiological role for the t system.…”

Section: Discussionmentioning

confidence: 97%

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The accessibility and interconnectivity of the tubular system network in toad skeletal muscle

Edwards

Launikonis

2008

The Journal of Physiology

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The tubular (t) system is essential for normal function of skeletal muscle fibre, acting as a conduit for molecules and ions within the cell. However, t system accessibility and interconnectivity have been mainly assessed in fixed cells where the t system no longer fully represents that of the living cell. Here, fluorescent dyes of different diameter were allowed to equilibrate within the t system of intact fibres from toad, mechanically skinned to trap the dyes, and then imaged using confocal microscopy to investigate t system accessibility and interconnectivity. Dual imaging of rhod-2 and a 500 kDa fluorescein dextran identified regions throughout the t system that differed in the accessibility to molecules of different molecular weight. Restrictions within the t system lumen occurred at the junctions of the longitudinal and transverse tubules and also where a transverse tubule split into two tubules to maintain their alignment with Z-lines of adjacent mis-registered sarcomeres. Thus, three types of tubule, transverse, longitudinal and Z, can be identified by their lumenal diameter in this network. The latter we define for the first time as a tubule with a narrow lumen that is responsible for the change in register. Stretch-induced t system vacuolation showed exclusive access of rhod-2 to these structures indicating their origin was the longitudinal tubules. Exposing the sealed t system to highly hypertonic solution reversed vacuolation of longitudinal tubules and also revealed that these tubules are not collapsible. Fluorescence recovery after photobleaching (FRAP) measurements of t system-trapped fluo-5 N showed interconnectivity through the t system along the axis of the fibre. However, diffusion occurred at a rate slower than expected given the known number of longitudinal tubules linking adjacent transverse tubules. This could be explained by the observed narrow opening to the longitudinal tubules from transverse tubules, reducing the effective cross-sectional area in which molecules could move within the t system.

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Section: Resultsmentioning

confidence: 92%

Section: Resultsmentioning

confidence: 99%

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The accessibility and interconnectivity of the tubular system network in toad skeletal muscle

Edwards

Launikonis

2008

The Journal of Physiology

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“…To differentiate sarcoplasmic reticula (SR) and transverse tubules (T-tubules), 3 mice were used and TA muscles were treated with lanthanum [8][9][10][11][12][13][14][15] . At 3 hours after the transection, these animals were sacrified under the anesthesia by intracardiac perfusion initially with 0.1 M cacodylate buffer (pH 7.4), followed by a fixative containing 2.5% glutaraldehyde dissolved in the cacodylate buffer.…”

Section: Methodsmentioning

confidence: 99%

Repairing Process in the Transected Muscle Fibers of the Mouse Tibialis Anterior

Matsumoto

Matsubara

Miki

2007

J Jpn Phys Ther Assoc

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Repairing process at the injury site in the transected muscle fibers of the mouse tibialis anterior was studied by light and electron microscopy. Immediately after the transection, the cut end (approximately 10 µm) was filled with dense network of disorganized myofilaments, in which disrupted membranous structures and degraded mitochondria were scattered. In the portion next to the portion exhibiting sudden necrotic changes, morphological features of the myofilaments, mitochondria and membranous structures appeared to be almost normal. The degradation of disorganized myofilaments at the cut end began within 1 hour after the transection, and at 1hour after the transection, the degenerating areas were noted in most of muscle fibers up to 150-250 µm from the cut end. Following the degradation, accumulation of mitochondria occurred between the necrotic and myofilament-predominant living portions, and several transverse tubules (T-tubules) and sarcoplasmic reticula were found between the mitochondria-accumulated and myofilament-predominant areas. In most cases, demarcation membrane formed between the mitochondria-accumulated and myofilament-predominant areas, and the fusion of T-tubules and sarcoplasmic reticula was encountered in these areas, suggesting that at least some parts of the demarcation membranes formed through fusion of T-tubules and sarcoplasmic reticula. This repairing process was completed in a number of muscle fibers within 6 hours after the transection. Macrophages were first found in the injured portions at 6 hours after the transection, increased in number with time, and several macrophages were distributed at 1 to 3 days after the transection. Some spindle-shaped cells were first found in the degenerating portions of the muscle fibers at 1 day after the transection. Since they were located along the basal lamina of the muscle fiber, and had a long oval pale nucleus and relatively abundant cytoplasm, they can be regarded as activated satellite cells. They gradually increased in number with time, and became larger and longer. On and after 5 days, thin regenerating muscle fibers exhibiting centrally located nuclei were observed, and they became gradually thicker with time. These findings indicate that the muscle regeneration was actively occurring during these periods. The repairing process is followed by the invasion of macrophages, and then the occurrence of muscle regeneration in the sequential order. These findings suggest that there might be close chronological relationship among these events.

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Early effects of carbachol on the morphology of motor endplates of mammalian skeletal muscle fibers

Voigt

2009

Muscle and Nerve

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Long-term disturbance of the calcium homeostasis of motor endplates (MEPs) causes necrosis of muscle fibers. The onset of morphological changes in response to this disturbance, particularly in relation to the fiber type, is presently unknown. Omohyoid muscles of mice were incubated for 1-30 minutes in 0.1 mM carbachol, an acetylcholine agonist that causes an inward calcium current. In these muscles, the structural changes of the sarcomeres and the MEP sarcoplasm were evaluated at the light-and electron-microscopic level. Predominantly in type I fibers, carbachol incubation resulted in strong contractures of the sarcomeres underlying the MEPs. Owing to these contractures, the usual beret-like form of the MEP-associated sarcoplasm was deformed into a mushroom-like body. Consequently, the squeezed MEPs partially overlapped the adjacent muscle fiber segments. There are no signs of contractures below the MEPs if muscles were incubated in carbachol in calcium-free Tyrode's solution. Carbachol induced inward calcium current and produced fiber-type-specific contractures. This finding points to differences in the handling of calcium in MEPs. Possible mechanisms for these fiber-type-specific differences caused by carbachol-induced calcium entry are assessed.Carbachol is an acetylcholine agonist. When applied chronically, it causes a profound destruction of the myofibrils underlying the motor endplate (MEP). This effect is attributable to dissolution of the Z-line.1,2 The pathological changes are reputed to be calcium-dependent 1,2 and are comparable with those manifested in patients with slow-channel syndrome.3 Similar calcium-dependent destruction of the myofibrils beneath the MEP can be elicited by daily application of an acetylcholinesterase inhibitor. 4,5 The effect is brought on by prolonged opening of the acetylcholine receptors (AChRs) and ensuing entry of calcium in the area of the MEP. A genetic manipulation of the AChRs that prolongs the opening time of the receptor channels causes a slow-channel-syndrome-like pathology in mice.6 However, not all skeletal muscle fibers are affected.6 This selectivity accords with observations relating to the effects of carbachol. 1,2According to earlier data, carbachol affects preferentially type I fibers. This, combined with the observation that type I fibers are predominantly damaged by ACh esterase inhibitors, 4 suggests a greater vulnerability to calcium homeostasis in these fibers.Little is known of the early morphological changes associated with short-term carbachol stimulation. To improve our understanding of the disturbances in MEP calcium homeostasis that are elicited by the entry of calcium through activated AChRs, it would be beneficial to temporally and topographically pinpoint the first visible signs of damage and to ascertain whether the changes are fiber-specific. To address these questions, the omohyoid muscle of mice was stimulated with carbachol under isometric conditions for 1-30 minutes. The treated muscles were evaluated at the light-and transmissi...

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About the T-system in the myofibril-free sarcoplasm of the frog muscle fibre

Cited by 7 publications

References 18 publications

The accessibility and interconnectivity of the tubular system network in toad skeletal muscle

The accessibility and interconnectivity of the tubular system network in toad skeletal muscle

Repairing Process in the Transected Muscle Fibers of the Mouse Tibialis Anterior

Early effects of carbachol on the morphology of motor endplates of mammalian skeletal muscle fibers

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