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Biomedical subjects

R Libelius

Publications and source records attributed to R Libelius.

16 recordsLinked to original sources
PubMed1992

Dextrans as markers for endocytosis in innervated and denervated skeletal muscle.

Fluorescence-labeled dextrans were evaluated as markers for endocytosis in skeletal muscle. Fluorescein isothiocyanate (FITC)-labeled dextrans (average molecular weight 3900 to 71200) showed a higher uptake in denervated than in innervated muscle both in vitro and in vivo. The in vitro uptake of FITC-dextran (35.600) increased linearly with time at 37 degrees C, and was almost completely inhibited by low temperature (4 degrees C). The uptake was not a pure bulk uptake, because a saturable component was evident from the concentration dependence and from competition experiments with unlabeled dextran. The uptake of FITC-labeled or rhodamine B isothiocyanate (RITC)-labeled dextrans in denervated muscle occurred mainly in small segments of the fibers centered around the denervated endplate region. However, not all denervated fibers showed such segments. Periodic acid Schiff's base staining for carbohydrates stained dextrans in denervated muscle fibers. Some staining, probably of lysosomes, was also observed in denervated muscle not exposed to dextran.

Animals↗
PubMed1992

Increased endocytotic and lysosomal activities in denervated type I and type II muscle fibres.

Previous work has shown that increased endocytotic and lysosomal activities occur in the endplate region of denervated skeletal muscle fibres. This, however, does not engage all fibres of a muscle at a given time after denervation. The present study was carried out in order to determine if both type I (slow) and type II (fast) muscle fibres can react to denervation by increased endocytotic and lysosomal activities. Uptake of horseradish peroxidase as a marker for endocytosis was studied in conjunction with acid phosphatase staining for lysosomal activity in type I and type II fibres of the denervated mouse hemidiaphragm. Fibre typing was performed using a monoclonal antibody against fast skeletal myosin and by adenosine triphosphatase staining. The results show that increased endocytosis and lysosomal activation occur in both type I and type II fibres after denervation.

Acid Phosphatase↗
PubMed1992

Trapezius muscle changes unrelated to static work load. Chemical and morphologic controlled studies of 22 women with and without neck pain.

From a cross-sectional study of 82 women who were engaged in assembly work that involved static muscle loading of the shoulder muscles, 11 cases with complaints of neck tension (all except 1 arising at work) and 11 individually matched, exposed control cases without neck pain were studied. In addition, 10 matched, unexposed control cases were studied. Upon histochemical examination and study of the trapezius muscle, morphologic changes of type ragged red fibers were found in 8/11 neck-pain cases, in 7/11 exposed controls, and in 4/10 unexposed controls. The pathologic and clinical importance of rare, ragged red fibers in the trapezius muscle thus seems uncertain.

Adult↗
PubMed1990

High endocytotic and lysosomal activities in segments of rat myotubes differentiated in vitro.

Endocytosis and the lysosome system have been studied in rat myotubes differentiated in vitro. Horseradish peroxidase was used as marker for endocytosis and was found to accumulate unevenly in the myotubes. Small segments of myotubes display very high endocytotic activity. Similar segments contained numerous lysosomes, as seen by the accumulation of neutral red or histochemical staining for acid phosphatase. The segments also contained accumulations of acetylcholine receptors as determined by binding of tetramethyl rhodamine-labelled alpha-bungarotoxin. Unstained segments in living cultures could be recognized by phase-contrast microscopy since they often appeared somewhat dilated and were not as well spread on the culture surface as the main parts of the myotubes. Ultrastructurally, the segments contained an intensely proliferating tubular system in communication with the extracellular space, which therefore probably represents the developing transverse tubular system. The segments also contained endocytosed marker within large phagosomes. Contractile filaments occurred in the segments but were frequently less well-organized than in other parts of the myotubes. The described characteristics of the segments in rat myotubes differentiated in vitro bear resemblance to some of the characteristics of the denervated endplate region of adult muscle.

Animals↗
PubMed1986

An ultrastructural study of the segmental uptake of horseradish peroxidase in the endplate region of denervated skeletal muscle fibres.

The segmental uptake of horseradish peroxidase (HRP) in the endplate region of denervated skeletal muscle fibres has been studied ultrastructurally using a method for selecting single muscle fibres with high segmental peroxidase staining from denervated mouse tibialis anterior muscle. Segments containing large peroxidase positive phagosomes could already be seen 10-15 min after i.v. injection of HRP. Such segments were still present 24 h after HRP injection. The localization of phagosomes, deep in the fibres rather than immediately under the sarcolemma, suggests that the uptake occurs from t-tubuli. Vivid proliferation of t-tubuli, consisting of vesiculation, enlargement and encircling of cytoplasmic components, was also observed. The HRP accumulates in phagosomes of varying size and shape. Similar membrane-limited bodies without or with very weak peroxidase staining were also observed. The peroxidase-positive phagosomes participate in autophagic processes as suggested by their content of undegraded cellular material. Golgi profiles, which occurred deep in the muscle fibres, and enlarged components of the sarcoplasmic reticulum were frequently encountered in the segments. Myofibrillar degeneration occurs in the segments and progresses with time after denervation. The described segments may be related to the increased membrane turnover in denervated muscle fibres and/or they may be related to processes aimed at establishing new synaptic contacts.

Animals↗
PubMed1979

T-tubule endocytosis in dystrophic chicken muscle and its relation to muscle fiber degeneration.

Pectoralis muscles from normal and dystrophic chickens were investigated 2 h after an i.v. injection of horseradish peroxidase, by cytochemical and biochemical techniques to demonstrate peroxidase activity. Light microscopic examination of dystrophic muscles showed that peroxidase activity could be detected inside a population of fibers, in deliminated bodies often restricted to segments of the muscle fiber. Such bodies containing peroxidase were not observed in normal muscle fibers. Electron microscopy of dystrophic muscle fibers revealed that numerous vesicles containing peroxidase were frequently present in fiber regions with signs of cytoplasmic degradation. These vesicles, which occasionally were found to be coated, were 50--100 nm in size and appeared to be derived from t-tubules. Larger (up to 1.7 micrometers) inclusions containing peroxidase and delimited by a single membrane were also present at degenerating areas of dystrophic muscle fibers. These bodies seemed to be formed by fusion between several primary t-tubule vesicles and probably also lysosomes. Vacuoles containing the peroxidase were frequently encountered. Biochemical determination of horseradish peroxidase activity, performed after extensive washing of the muscle tissue, showed that dystrophic muscles contained about twice as much peroxidase as normal control muscles. It is suggested that endocytosis from t-tubules is an early and essential pathological phenomenon in dystrophic muscle fibers, which may be related to lysosomal function and muscle fiber degeneration

Animals↗
PubMed1978

Lysosomal activation in mouse skeletal muscle induced by protamine in vitro.

Incubation of mouse skeletal muscle in a physiological Ringer solution containing protamine (60 microgram/ml) at +37 degrees C for 1 h induced ultrastructural changes including proliferation of tubular profiles and vesicles at the I-band level close to the A-I junction, formation of numerous acid phosphatase positive lysosomes in the longitudinal sarcoplasmic reticulum and autophagic vacuolation starting at the level of the A-I junction. Biochemical determination of acid phosphatase in the incubated muscles showed that protamine caused an increase in acid phosphatase activity of about 25% compared to enzyme activities obtained from muscles incubated without protamine at +37 degrees C or with protamine at +4 degrees C. The morphological findings suggest that the vesicles arising adjacent to the A-I junction originate from transverse tubules. Such vesicles, designated as endocytic, may acquire acid phosphatase activity in the longitudinal SR ano be active in an autophagic process resulting in large vacuoles. A causal relationship between endocytosis and lysosomal activation is suggested.

Acid Phosphatase↗
PubMed1977

Protamine induced intracellular uptake of horseradish peroxidase and vacuolation in mouse skeletal muscle in vitro.

The uptake in vitro of horseradish peroxidase (HRP) in mouse skeletal muscle was examined by electron microscopy and chemical determination. In muscles exposed to an HRP solution for 60 min at +37 degrees C, HRP infiltrated the basal lamina of muscle fibres and caused an intense labelling of their sarcolemma. In addition HRP was found within the transverse tubules. Exposure to HRP for 30 min at +37 degrees C followed by HRP together with a polycationic protein (protamine) for 30 min at +37 degrees C caused an intracellular vesicular uptake of HRP. Intracellular HRP was found in numerous vesicles, membrane limited bodies and vacuoles. Protamine also induced focal autophagic vacuolation with progressive muscle fibre degeneration. An intracellular HRP uptake or muscle cell vacuolation could not be detected in the absence of protamine or when the incubation temperature was +4 degrees C. Chemical determination of HRP uptake was in general agreement with the morphological results. The uptake of HRP in the presence of protamine was stimulated at +37 degrees C and blocked at +4 degrees C. The results suggest that in skeletal muscle in vitro intracellular uptake of macromolecules occurs by endocytosis.

Animals↗
PubMed1977

Acetylcholine receptor protein. Neuromuscular transmission in immunized rabbits.

Rabbits injected with purified acetylcholine (ACh) receptor protein produce antibodies against the receptor and develop generalized muscle weakness. The compound muscle action potentials show a decremental fall in amplitude with repetitive nerve stimulation. Both the weakness and the decrement is counteracted by reversible cholinesterase inhibitors. Intracellular recordings from muscle endplates show that the amplitude of the miniature end-plate potentials is considerably reduced. A reduced binding of neurotoxin to muscles from immunized rabbits was observed. Nerve impulses release a normal number of ACh packages (quanta) from the motor nerve terminals. The muscle weakness in immunized rabbits thus has the same features as the muscle weakness in myasthenia gravis and may be a good animal model of myasthenia gravis.

Acetylcholine↗
PubMed1975

Evidence for endocytotic uptake of cobra neurotoxin in mouse skeletal muscle.

An isolated 3H-labelled neurotoxin from Naja naja siamensis binds irreversibly to the extensor digitorum longus muscle of the mouse in vitro. The binding consists of an adsorption to cholinergic receptors and of a slower temperature sensitive binding mechanism. The slow binding is markedly stimulated by the presence of cationic proteins (protamine, histone and polylysine) and is blocked at low temperature (+4 degrees C). Vinblastine and colchicine inhibit the stimulatory effect of protamine on the slow binding. Unlabelled neurotoxin blocks the adsorption binding but fails to affect the slow binding. The results suggest that the slow binding of neurotoxin is not associated with the presence of cholinergic receptors but is the result of endocytotic uptake into the muscle cell. Unless properly recognized this uptake will give a considerable overestimate of the number of cholinergic receptors present in the muscle.

Animals↗
PubMed1975

Further studies on the binding properties of cobra neurotoxin to cholinergic receptors in mouse skeletal muscle.

Preparations of 3H-monoacetylated derivatives of Naja naja siamensis neurotoxin siamensis 3 were found to be resistant to degradation and deacetylation during in vitro muscle incubation. A low rate of free 3H-acetate (less than 0.4%) was present in the preparations, but should not interfere with the binding of toxin to cholinergic receptors in mouse extensor digitorum longus muscles in vitro. The binding of toxin to cholinergic receptors in mouse extensor digitorum longus muscle was essentially irreversible. d-Tubocurarine antagonized the binding of toxin in both innervated and denervated muscles. Administration of actinomycin D one day after denervation prevented the appearance of new toxin binding sites in the muscles.

Animals↗
PubMedDate not supplied

Increased endocytosis with lysosomal activation in skeletal muscle of dystrophic mouse.

Endocytosis in dystrophic muscles was studied by a combination of biochemical, radiochemical, and light and electron microscopic techniques. It was observed that the uptake of horseradish peroxidase (HRP) and 3H-Inulin in vitro was increased in leg skeletal muscles from dystrophic mice compared with littermate controls. Endocytosis of HRP in vivo was also increased in dystrophic muscles. When HRP was administered intravenously, light microscopic examination of the muscles showed that the macromolecular tracer was present not only in the extracellular space but also as intracellular deposits in several dystropic muscle fibers. Ultrastructural examination of these fibers showed HRP to be present in membrane limited bodies of variable size, some of which likely represented secondary lysosomes, located preferentially close to the A-I junction. HRP was also found inside vacuoles which were sometimes in close vicinity to autophagic vacuoles. Primary uptake vesicles containing HRP appeared to originate from the sarcolemma and the transverse tubules. Biochemical determination of lysosomal enzyme activities revealed elevated levels of both cathepsin D and N-acetylglucosaminidase in dystrophic muscles as compared with controls. The results suggest an increased endocytic activity in dystrophic muscles with distribution of exogenous marcromolecular tracers into endocytic vesicles and lysosomal structures. The hypothesis is put forward that endocytic activity constitutes an important mechanism of lysosomal activation in dystrophic muscles.

Acetylglucosaminidase↗