Myosin VI in skeletal muscle: its localization in the sarcoplasmic reticulum, neuromuscular junction and muscle nuclei.

Myosin VI (MVI) is a unique unconventional motor moving backwards on actin filaments. In non-muscle cells, it is involved in cell migration, endocytosis and intracellular trafficking, actin cytoskeleton dynamics, and possibly in gene transcription. An important role for MVI in striated muscle functioning was suggested in a report showing that a point mutation (H236R) within the MVI gene was associated with cardiomyopathy (Mohiddin et al.

[Hyperthyreosis inhibits the ability of actin to form strong-binding with myosin].

The effect of hyperthyreosis development induced by the increase in thyroid hormones in rats (during 2-4 weeks) on the orientation and mobility of fluorescent probe N-(iodoacetyl)-(1-naphtyl-5-sulpho-ethylenediamine) specifically bound to Cys 374 of actin in ghost muscle fibers isolated from fast (EDL) and slow (SOL) rat muscles was studied. It was found that the binding of myosin subfragment-1 (S1) to F-actin induced the typical for the formation of strong binding actomyosin decrease in mobility of actin subdomain 1 and its rotation towards thin filament periphery. Development of hyperthyreosis markedly inhibited these phenomena.

[Effect of hypothyreosis on actin subdomain-1 movement induced by myosin subfragment 1-binding in fast and slow rat skeletal muscles].

Orientation and mobility of fluorescent probe N-((iodoacetyl)-(1-naphtyl-5-sulpho-ethylenediamine)(1.5-IAEDANS)) specifically bound to Cys-374 of actin in ghost muscle fibers isolated from fast and slow rat muscles were studied by polarized fluorimetry in the absence and presence of myosin subfragment-1 (S1) in intact rats and in the animals with gradual (during 2-5 weeks) reduction of thyroid hormones synthesis (hypothyreosis development). S1 binding to F-actin of ghost muscle fibers was shown to induce changes in orientation of the dipoles of the fluorescent probe 1.

Influence of locomotor training on the structure and myosin heavy chains of the denervated rat soleus muscle.

Objective: Mechanism of denervation atrophy remains poorly understood. In particular, the question about irreversibility of the late atrophy is still open. Therefore, in the present study, we investigated whether and how a passive movement can affect a progress of atrophy in rat soleus muscle.

[The influence of caldesmon on strong binding of myosin with actin in denervated rat skeletal muscles].

The effect of caldesmon (CaD) on conformational changes in F-actin modified by fluorescent probe TRITC-phalloidin was investigated by polarized fluorimetry. Changes were induced by a subfragment-1 (S-1) of myosin in the absence or presence of CaD in ghost muscle fibers obtained from intact and denervated slow (SOL) and fast (EDL) skeletal muscles of rats. S-1 binding to actin of both SOL and EDL muscles was shown to cause changes in polarized parameters of TRITC-phalloidin typical for a strong actin-myosin binding as well as of transition ofactin subunits from "off" to "on" state.

Deficiency of alpha-sarcoglycan differently affects fast- and slow-twitch skeletal muscles.

Alpha-sarcoglycan (Sgca) is a transmembrane glycoprotein of the dystrophin complex located at skeletal and cardiac muscle sarcolemma. Defects in the alpha-sarcoglycan gene (Sgca) cause the severe human-type 2D limb girdle muscular dystrophy. Because Sgca-null mice develop progressive muscular dystrophy similar to human disorder they are a valuable animal model for investigating the physiopathology of the disorder.

Ultrastructure of diaphragm from dystrophic alpha-sarcoglycan-null mice.

alpha-Sarcoglycan is a 50 kDa single-pass transmembrane glycoprotein exclusively expressed in striated muscle that, together with beta-, gamma-, and delta-sarcoglycan, forms a sub-complex at the muscle fibre cell membrane. The sarcoglycans are components of the dystrophin-associated glycoprotein (DAG) complex which forms a mechanical link between the intracellular cytoskeleton and extracellular matrix. The DAG complex function is to protect the muscle membrane from the stress of contractile activity and as a structure for the docking of signalling proteins.

Loss of dystrophin and some dystrophin-associated proteins with concomitant signs of apoptosis in rat leg muscle overworked in extension.

This study investigated the basis for the high severity of damage to skeletal muscle due to eccentric exercise, i.e., to muscles generating force while lengthened.

Effect of thyroid hormone on the myosin heavy chain isoforms in slow and fast muscles of the rat.

The myosin heavy chain (MHC) was studied by biochemical methods in the slow-twitch (soleus) and two fast-twitch leg muscles of the triiodothyronine treated (hyperthyroid), thyroidectomized (hypothyroid) and euthyroid (control) rats. The changes in the contents of individual MHC isoforms(MHC-1, MHC-2A, MHC-2B and MHC-2X) were evaluated in relation to the muscle mass and the total MHC content. The MHC-1 content decreased in hyperthyreosis, while it increased in hypothyreosis in the soleus and in the fast muscles.

Contents of myosin heavy chains in denervated slow and fast rat leg muscles.

The total content of myosin heavy chain (MHC) and individual MHC isoforms were studied in 14-day denervated rat leg muscles: the slow-twitch (soleus) and fast-twitch (extensor digitorum longus and gastrocnemius) by biochemical methods. The weight of the denervated muscles decreased by about 50%, as compared to the control muscles. In all denervated muscles the total content of MHCs decreased, more so in the slow than in the fast muscles.

Effects of denervation and muscle inactivity on the organization of F-actin.

To discriminate between the influences of a motoneuron and muscle activity on the conformation of actin filaments, the extrinsic polarized fluorescence [of rhodamine-phalloidin and N-(iodoacetylamine)-1-naphthylamine-5-sulfonic acid attached to F-actin] was measured in "ghost" fibers from intact rat soleus muscles and atrophying muscles after denervation, immobilization, or tenotomy. The results show that the conformation of F-actin changed in all the atrophying muscles, but differently. In the denervated muscle, the flexibility of the actin filaments decreased, whereas in the other experimental muscles it remained as in the intact muscle.

Ultrastructure of mechanically tenderised pork muscle.

Porcine biceps femoris muscles were mechanically tenderised by the use of a meat activator. The kind and degree of damage of muscle tissue were then examined under an electron microscope. It was observed that several changes, known from the studies of the post mortem muscles, were much more frequent in tenderised than in intact muscles.

Changes in myosin and actin filaments in fast skeletal muscle after denervation and self-reinnervation.

1. Myosin and actin filaments of the contractile apparatus of the denervated and self-reinnervated rat leg fast muscle were examined in ultrastructure. In parallel, the total contents of actin and of myosin heavy chains (MHC) were investigated.

Myosin heavy-chain composition in striated muscle after tenotomy.

The myosin heavy-chain (MHC) isoform pattern was studied by biochemical methods in the slow-twitch (soleus) and fast-twitch (gastrocnemius) muscles of adult rats during atrophy after tenotomy and recovery after tendon regeneration. The tenotomized slow muscle atrophied more than the tenotomized fast muscle. During the 12 days after tenotomy the total MHC content decreased by about 85% in the slow muscle, and only by about 35% in the fast muscle.

Remodelling of the contractile apparatus of striated muscle stimulated electrically in a shortened position.

The aim of this study was to examine reorganisation of the contractile apparatus during adaptation to function when the length of a muscle is decreased. The rat soleus muscle was maintained in a shortened position and simultaneously stimulated electrically at a low frequency for 1-45 h. This experimental model decreased the length of the muscle and made the contractile apparatus irregular.

Myosin heavy chain isoform composition in striated muscle after denervation and self-reinnervation.

The total content of myosin heavy chains (MHC) and their isoform pattern were studied by biochemical methods in the slow-twitch (soleus) and fast-twitch (extensor digitorum longus) muscles of adult rat during atrophy after denervation and recovery after self-reinnervation. The pattern of fibre types, in terms of ultrastructure, was studied in parallel. After denervation, total MHC content decreased sooner in the slow-twitch muscle than in the fast-twitch.

Ultrastructure of the contractile apparatus of rat skeletal muscle embedded in an aqueous medium.

The method of tissue embedding in melamine resin was applied to rat skeletal muscle. This method does not require tissue dehydration with organic solvents; only aqueous solutions are used. Electron micrographs of muscles embedded in melamine differ from those embedded in the conventional epoxy resin.

Effect of denervation, reinnervation and hypertrophy on the state of actin filaments in skeletal muscle fibres.

The conformational state of actin filaments was studied in the rat soleus muscle atrophying after denervation, recovering following reinnervation, hypertrophying following tenotomy of synergists and in intact muscle. Intrinsic (tryptophan residues of F-actin) and extrinsic (rhodamine-phalloidin or 1,5-IAEDANS attached to F-actin) polarized fluorescence was measured. In parallel, the influence of ATP or NEM on the state of F-actin was studied.

Degradation of alpha-actinin during Ca2+-sensitive proteolysis of myofibrils.

The noted loss of alpha-actinin from the Z-line of myofibrils during post-mortem autolysis, probably following the action of calcium-activated protease, has previously been attributed to its release without degradation. This report shows that in isolated myofibrils alpha-actinin is proteolysed in a Ca2+-sensitive manner presumably via the action of calcium-activated protease.

Reconstruction of the contractile apparatus of striated muscle. I. Muscle maintained in extension.

The ultrastructure of the contractile apparatus was observed in muscles maintained in excessive extension, i.e. in conditions in which an increase takes place in the number of sarcomeres.