257 research outputs found
Effects of the spinal cord section and of subsequent denervation on the mechanical properties of fast and slow muscle
No full textThe Soleus muscle of the rat, 3--6 months old, becomes significantly faster than in the controls, if the spinal cord is cut at birth. Mechanical properties of Extensor Digitorum Longus (EDL) muscle are not altered by spinal cord section. In cordotomized animals Soleus muscle always remains slower than EDL muscle. Denervation, performed 3--6 months after birth, has the same slowing effects in the Soleus and EDL muscles, both in cordotomized and in the control animals
Effects of two synaptic activators, calcium and ethanol, on MEPP'S distribution in time
No full textMiniature end-plate potentials (MEPPs) were recorded intracellularly from sartorius muscle of Rana esculenta. Tracings were divided into time bins whose duration approximated one-fifth of the mean interval between consecutive potentials. The observed number of bins containing 0, 1, 2, ... MEPPs was compared, by the X2 test, with the number calculated from the Poisson equation. MEPP timing was analyzed in the absence as well in the presence of Ca2+ (1 mM, 2.5 MM, and 15 mM). In half of the experiments, 0.5% ethanol was added to the bathing solution. In the absence of Ca2+, MEPP timing fitted the Poisson predictions. On adding Ca2+, the fit became poor and MEPPs showed the tendency to cluster. At 15 mM Ca2+, no experiment proved to be Poissonian. Though increasing the frequency of MEPPs similarly to Ca2+, ethanol maintained a Poissonian release of transmitter at any concentration of Ca2+. It is suggested that ethanol masks the effects of Ca2+ on MEPP timing by also inducing the discharge of transmitter outside the Ca2+-dependent sites of exocytosis in the presynaptic membrane
Type 1, 2A, 2B myosin haevy chain electrophoretic analysis of rat muscle fibers
No full textMammalian skeletal muscles are mixture of three type of fibers: type 1, type 2A, and type 2B fibers. Immunological studies and proteolytic analysis of myosin heavy chains from the three type of fibers have demonstrated the presence of distinct myosin isoforms. By using typed single muscle fibers and improving an electrophoretic method we are able to resolve three distinct polypeptides which are demonstrate to correspond to type 1, 2A and 2B myosin heavy chain isoforms by using specific monoclonal antibodies. The analysis of single muscle fibers shows that different myosin heavy chain isoforms are frequently coexpressed in the same muscle fiber
The regenerating muscle as an experimental model for the study of factors which affect muscle differentiation or adaptation
No full textBupivacaine-induced regeneration was studied in the rat soleus muscle in the presence or absence
of innervation, in the presence of tetrodotoxin (TTX)-induced block of nerve impulse
conduction, and/or in the presence of vinblastine-induced block of nerve axoplasmic flow.
Part of experiments were carried out on tenotomized muscles. Regenerated muscles were
analysed for myosin heavy chain (MHC) composition 14 days after bupivacaine injection. In
TTX-paralysed-regenerated muscles type 1 and type 2A MHC isoforms were not expressed.
In denervated-regenerated muscles type 1 isoform was lacking, while all fast isoforms (2A,
2B, 2X) were expressed. Tenotomy alone increased type 2A fibres, but did not modify the effects
of surgical or functional denervation. Vinblastine-block caused up-regulation of 2A isoform
expression in non-tenotomized muscles. The results confirm the essential role played by
neuromotor impulses for type 1 and type 2A isoform expression. They also support the
hypothesis that axoplasmic flow carries some chemical factor inhibiting 2A isoform expression
The role of sphingolipids in the control of skeletal muscle function: a review.
No full textIn this review, potential roles for the endogenous sphingolipid, sphingosine, and its derivatives are described for muscle cells. Sphingosine modulates the function of important calcium channels in muscle, including the ryanodine receptor (RyR) calcium release channel of the sarcoplasmic reticulum (SR). Sphingosine blocks calcium release through the SR ryanodine receptor and reduces the activity of single skeletal muscle RyR channels reconstituted into planar lipid bilayers. Sphingosine-blocked calcium release is coincident with the inhibitory effects of sphingosine on [3H]ryanodine binding to the RyR. The sphingomyelin signal transduction pathway has also been identified in both skeletal and cardiac muscle. A neutral form of sphingomyelinase (nSMase) enzyme has been localized to the junctional transverse tubule membrane. The high turnover of the SMase is responsible for the production of ceramide and sphingosine. HPLC analyses indicate that significant resting levels of sphingosine are present in muscle tissue. A model of excitation-contraction coupling is presented suggesting a potential role for this endogenous sphingolipid in normal muscle function. Putative roles for sphingolipid mediators in skeletal muscle dysfunction are also discussed. We hypothesize that sphingosine plays important roles in malignant hyperthermia and during the development of muscle fatigue
Polimorphism of myofibrillar proteins of rabbit skeletal muscle fibres. An electrophoretic study of single fibres
No full textRabbit predominantly fast-twitch-fibre and predominantly slow-twitch-fibre skeletal muscles of the hind limbs, the psoas, the diaphragm and the masseter muscles were fibre-typed by one-dimensional polyacrylamide-gel electrophoresis of the myofibrillar proteins of chemically skinned single fibres. Investigation of the distribution of fast-twitch-fibre and slow-twitch-fibre isoforms of myosin light chains and the type of myosin heavy chains, based on peptide 'maps' published in Cleveland. Fischer, Kirschner & Laemmli [(1977) J. Biol. Chem. 252, 1102-1106], allowed a classification of muscle fibres into four classes, corresponding to histochemical types I, IIA, IIB and IIC. Type I fibres with a pure slow-twitch-type of myosin were found to be characterized by a unique set of isoforms of troponins I, C and T, in agreement with the immunological data of Dhoot & Perry [(1979) Nature (London) 278, 714-718], by predominance of the beta-tropomyosin subunit and by the presence of a small amount of an additional tropomyosin subunit, apparently dissimilar from fast-twitch-fibre alpha-tropomyosin subunit. The myofibrillar composition of type IIB fast-twitch white fibres was the mirror image of that found for slow-twitch fibres in that the fast-twitch-fibre isoforms only of the troponin subunits were present and the alpha-tropomyosin subunit predominated. Type IIA fast-twitch red fibres showed a troponin subunit composition identical with that of type IIB fast-twitch white fibres. On the other hand, a unique type of myosin heavy chains was found to be associated with type IIA fibres. Furthermore, the myosin light-chain composition of these fibres was invariably characterized by a small amount of LC3F light chain and by a pattern that was either a pure fast-twitch-fibre light-chain pattern or a hybrid LC1F/LC2F/LC3F/LC1Sb light-chain pattern. By these criteria type IIA fibres could be distinguished from type IIC intermediate fibres, which showed coexistence of fast-twitch-fibre and slow-twitch-fibre forms of myosin light chains and of troponin subunits
Different expression of sphingosine 1-phosphate receptor 1 in skeletal muscle in relation to gender, age and use.
No full textSphingosine 1-phosphate (S1P) is a bioactive signaling lipid that regulates important cellular processes, including proliferation, survival, growth, differentiation and migration. The extracellular action of S1P is mediated by the binding to five high-affinity G proteincoupled receptors (S1P1-5) that generate multiple downstream signals. In skeletal muscle, we demonstrated that S1P1 and S1P3 receptors are localized in the plasma and T-tubule membranes, consistently with a trophic action exerted by S1P in denervated muscle (Zanin et al. Am J Physiol 294:C36–46, 2008). These receptors are also evident at the
neuromuscular junction level and in the nuclear membrane. S1P1 and S1P3 are also demonstrated in quiescent satellite cells, whereas S1P2 receptor is only transitorily expressed in activated satellite cells, validating the role of S1P in muscle regeneration (Danieli-Betto et al. Am J Physiol 298:C550–8, 2010). In the present work we analyzed
the expression of S1P1 receptor in different muscles and conditions. Western blot analysis shows that rat and mouse muscles express two different S1P1 protein bands, whose relative proportion depends on the muscle type (slow and fast), gender and age of animals. Moreover, denervation, regeneration and electrical stimulation differently affect
both the relative expression level and membrane-to nucleus localization of the two S1P1 forms. Funded by PRIN 2008
Calcium sensitivity and myofibrillar protein isoforms of rat skinned skeletal muscle fibres
No full textWe investigated the calcium sensitivity for tension generation of different fibre types and the possible correlation between calcium sensitivity and the presence of distinct regulatory protein and myosin light chain (MLC) isoforms in rat skinned skeletal muscle fibres. Fibre types 1, 2A and 2B were identified by electrophoretic analysis of myosin heavy chain (MHC) isoforms. Fibres showing more than one MHC isoform were discarded. Type 1 fibres from the soleus showed a higher pCa (-log10 [Ca], where [ ] denotes concentration) threshold and a lower slope of pCa/tension curve than type 2 extensor digitorum longus (EDL) fibres; between type 2 fibres, type 2B showed the higher slope of pCa/tension curve. Type 1 fibres from different muscles showed similar calcium sensitivities when containing only the slow set of regulatory proteins and MLC; when both slow and fast isoforms were present, calcium sensitivity shifted toward fast type fibre values. Type 2A fibres from different muscles showed a similar calcium sensitivity, independently of the set (purely fast or mixed) of regulatory proteins and MLC. It is suggested that when both fast and slow isoforms of regulatory proteins and of MLC are present in a muscle fibre, calcium sensitivity is dictated mainly by the fast isoforms
Effects of disuse and nerve stump length on the development of fibrillation in denervated soleus muscle
No full textBoth in normal (control) and in cordotomized (disused) rats, the soleus muscle was denervated either by cutting the sciatic nerve near the trochanter (proximal denervation) or by cutting the soleus nerve near the insertion into the muscle (distal denervation). In the control muscles, the development of fibrillation was not dependent on the level of nerve section. In disused muscles, the development of fibrillation was greater following distal denervation that following the proximal one
The use of osmotic minipumps to block impulse conduction in peripheral nerve and spontaneous activity in denervated skeletal muscle
No full text- …
