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S Thesleff

Publications and source records attributed to S Thesleff.

16 recordsLinked to original sources
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

4-Aminopyridine and evoked transmitter release from motor nerve endings.

1 In the presence of tetrodotoxin, electrotonic depolarization of frog motor nerve terminals causes the appearance of stimulus-graded endplate potentials. When 4-aminopyridine is added, the graded endplate potential is converted into a triggered all-or-none response resulting in giant endplate potentials of about 70 mV amplitude and 50 ms duration. The triggered endplate potentials are abolished in Ca(2+)-free saline and are blocked by Mn(2+) ions. Sr(2+) but not Ba(2+) can replace Ca(2+) in supporting transmitter release. Mg(2+) fails, even in concentrations as high as 32 mM, to affect the amplitude and the shape of the endplate potential but abolishes it when the Ca(2+) concentration is reduced to 0.2 mM.2 Despite the large amplitude of the triggered endplate potential in the presence of 4-aminopyridine and tetrodotoxin, repetitive stimulation up to 10 Hz causes only a small decline in amplitude of successive endplate potentials. However, in the presence of (+)-tubocurarine or gallamine, repetitive nerve stimulation produces a marked decline in successive endplate potential amplitude. The fall is counteracted when evoked transmitter release is reduced in the presence of 0.2 mM Ca(2+). The results suggest that in the presence of 4-aminopyridine such large amounts of transmitter are released that even during repetitive stimulation (5 to 10 Hz) endplate potentials are of maximal amplitude.3 4-Aminopyridine causes a prallel shift to the right of the dose-response curve to Mg(2+) for blockade of nerve impulse-evoked transmitter release (in the absence of tetrodotoxin). A similar parallel shift occurs in the presence of tetraethylammonium and guanidine.4 It is concluded that 4-aminopyridine increases transmitter release by enhancing the transport efficacy for Ca(2+) across the nerve terminal membrane during nerve terminal depolarization.

Aminopyridines↗
PubMed1978

Studies on neurotrophic regulation of murine skeletal muscle.

1. A quantitative comparison was made of the effects of the paralysis caused by botulinum toxin (BoTx) type A with those of surgical denervation on the development of tetrodotoxin (TTX) resistant action potentials and of extrajunctional acetylcholine (ACh) receptors in rat and mouse skeletal muscle.2. After surgical denervation, TTX resistant action potentials were present in all fibres on the third day and their rate of rise and amount of overshoot reached peak values at the fifth day. BoTx poisoning failed, despite causing complete paralysis, to induce TTX resistant action potentials in all fibres and their average rate of rise was at all times (4-12 days) only about half that in denervated fibres. Similarly BoTx poisoning induced a smaller increase than surgical denervation in the number of extrajunctional ACh receptors, measured as (3)H-labelled Naja naja siamensis alpha-neurotoxin binding sites.3. Surgical denervation of BoTx poisoned muscles induced TTX resistant action potentials in all fibres and their rate of rise and amount of overshoot were 2-3 times those in BoTx poisoned muscles only. Denervation also significantly increased the binding of labelled alpha-neurotoxin. These effects of denervation were prevented by the administration of actinomycin D, a blocker of protein synthesis.4. Administration of the alpha-neurotoxin to BoTx poisoned animals resulted in the appearance of TTX resistant action potentials in all fibres and in a significant increase in their rate of rise and overshoot.5. The results show that, despite causing complete paralysis, BoTx is less effective than surgical denervation in inducing denervatory changes in skeletal muscle. This suggests that the BoTx poisoned nerve has an influence which suppresses the appearance of denervation signs. Since the alpha-neurotoxin blocked this influence remaining release of ACh, quantal or non-quantal, may be responsible for this neurotrophic action.

Action Potentials↗
PubMed1977

Antagonism of the paralysis produced by botulinum toxin in the rat. The effects of tetraethylammonium, guanidine and 4-aminopyridine.

The injection of botulinum toxin type A into the hind-leg of adult rats causes complete paralysis of the leg lasting for several weeks. In the extensor digitorum longus (EDL) muscle transmitter release is reduced to a level of less than 1% of normal. Tetraethylammonium (TEA) and guanidine in concentrations of about 3 mM restore, in EDL muslces in vitro, neuromuscular transmission to about the normal level, provided that the external calcium concentration is 4 mM or higher. 4-Aminopyridine (4-AP) has similar restorative effect but is about 20-30 times more potent. Unlike TEA and guanidine, 4-AP is effective when the ambient calcium concentration is 2 mM; this drug is therefore also active in vivo. The intravenous injection of 4-AP (5 mg/kg body weight) restores neuromuscular transmission from complete paralysis by botulinum toxin to a normal level as shown by the recording of almost normal twitch and tetanic tensions in the EDL muscle. In rats paralysed by a lethal dose of botulinum toxin, the intraperitoneal administration of 4-AP restores general motor activity, the effect lasting 1-2 hours. A study of the effects of these drugs on spontaneous and evoked transmitter release suggests that all three compounds increase the level of free calcium inside the nerve terminals. In botulinum poisoning the transmitter release mechanism appears to be intact, but a reduced sensitivity to calcium has been shown (Cull-Candy et al. 1976), and this could explain why the drugs restore evoked transmitter release in botulinum poisoning.

Action Potentials↗
PubMed1976

Effects of botulinum toxin on neuromuscular transmission in the rat.

1. Botulinum toxin (BoTx) type A partially blocks spontaneous transmitter release from nerve terminals in the rat. Minature end-plate potentials (m.e.p.p.s) are present at all end-plates, initially with a low frequency but increasing with time after posoning. Their amplitude distribution is at first skew with a predominace of very small m.e.p.p.s but, after a few days, larger than normal m.e.p.p.s appear. 2. Tetanic nerve stimulation, Black Widow Spider Venom, the Caionophore A 23187 or mechanical damage to nerve terminals increases the frequency of m.e.p.p.s and alters the amplitude distribution of m.e.p.p.s towards a normal Gaussian one; the m.e.p.p. size approaches that seen at normal end-plates. This was seen at any time after poisoning. 3. Nerve stimulation gives rise to end-plate potentials (e.p.p.s) of low amplitude and high failure rate. Statistical analysis indicates that evoked release is quantal in nature and follows Poisson statistics, quantum size being initially very small, but after a few days approaching normal size. Short-term tetanic nerve stimulation reversibly increases the quantum content of e.p.p.s and during early stages of paralysis long-term (2 hr) stimulation causes an apparently permanent increase in quantum size. 4. Raising the extracellular Ca concentration from 2 to 16 mM increases the frequency of m.e.p.p.s in normal muscle but not in BoTx poisoned ones. K-free medium or ouabain, which are believed to raise the intracellular Ca concentration in nerve terminals, similarly increases m.e.p.p. frequency in normal but not in poisoned muscles. When the Ca-ionophore A 23187 is used together with high extracellular Ca (greater than 4 mM) massive release of transmitter occurs from poisoned terminals. 5. The extracellular Ca concentration which causes a certain level of transmitter release in reponse to nerve impulses is considerably higher at BoTx poisoned end-plates than at normal ones. The slope value for Ca dependence of transmitter release is about 1-5 compared with about 3 at normal end-plates. 6. Tetraethylammonium (TEA) greatly increases the amount of transmitter released by nerve impulses and restores neuromuscular transmission during all stages of poisoning, although it has not effect on spontaneous transmitter release. In the presence of TEA the power relation between Ca concentration and quantum content at the BoTx poisoned end-plate is similar to that seen at normal end-plates. 7. It is suggested that in BoTx poisoning the mechanism for transmitter release has a reduced sensitivity to Ca, and the level for activation by intracellular Ca is elevated. Once the intracellular concentration of Ca is raised to this level, by tetanic nerve stimulation, mechanical injury to nerve terminals, the Ca-ionophore or the prolongation of the nerve action potential with TEA, augmented transmitter release occurs, similar to that which occurs in normal nerve terminals at a lower level of Ca.

Animals↗
PubMed1975

Guanidine and neuromuscular transmission. I. Effect on transmitter release occurring spontaneously and in response to single nerve stimuli.

The effect of guanidine on neuromuscular transmission was studied in human intercostal muscle and mouse diaphragm preparations in vitro. Guanidine greatly increased the number of acetylcholine (ACh) quanta released by a single motor nerve action potential. This effect of guanidine was greater at junctions with a low quantum content. The spontaneous release of ACh quanta was not substantially changed by guanidine. No change was found in the postsynaptic sensitivity to ACh released from the motor nerve or iontophoretically applied to the muscle fiber. Effects of the drug had slow onset and were very long-lasting and resistant to wash.

Acetylcholine↗
PubMed1975

Guanidine and neuromuscular transmission. II. Effect on transmitter release in response to repetitive nerve stimulation.

The effect of guanidine on the neuromuscular transmission in human intercostal and mouse diaphragm muscle in vitro during repetitive nerve stimulation was studied. The drug greatly increased the release of acetylcholine (ACh) quanta by nerve impulses at low frequencies of nerve stimulation and at the beginning of tetani at high frequencies of stimulation. The effect was shown to be produced by an increase in fractional release from an unchanged store of ACh quanta available fro immediate release. This seems to explain why guanidine has a poor therapeutic effect in myasthenia gravis but a good effect in the myasthenic syndrome.

Acetylcholine↗
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↗