Seasonal variation in the phenotype of adult ferret (Mustela putorius furo) cremaster muscle

Using immunocytochemistry, electrophoresis and immunoblotting, we studied the expression of fast and slow myosin heavy chain isoforms in adult ferret muscles during quiescent and breeding periods. Adult cremaster muscle expressed slow and fast myosin heavy chain in relatively similar amounts during the quiescent period. During the breeding period, the expression of slow myosin heavy chain I, significantly decreased, and fast myosin heavy chain II, was predominant. No alteration of the MHC pattern in EDL and soleus muscles was detected between the quiescent and breeding periods. The possible involvement of androgens and mechanical factors in the regulation of myosin heavy chain expression in adult cremaster muscle is discussed.     

Spontaneous junctional currents in Drosophila muscle fibres: effects of temperature, membrane potential and ethanol.

Fast, slow and fast multiquantal spontaneous junctional currents were recorded from glutamate sensitive muscle fibres of Drosophila larvae. Decrease of temperature and hyperpolarization prolonged the time course of fast currents. Ethanol (0.4 M) markedly shortened their duration, whereas several other drugs known to modify the time course of currents at cholinergic synapses were ineffective at this neuromuscular junction.     

Myosin heavy chains in fast skeletal muscle of chick embryo

Summary The peptide map obtained by electrophoresis after digestion of purified myosin heavy chains from pectoralis muscle of embryonic chicken with theStaphylococcus aureus V8 protease, produces a peptide pattern very similar but not identical to that of adult fast myosin. In fact, some components that are present in a small amount in the map of slow adult myosin are visible in the embryonic pattern.Acknowledgments. I wish to acknowledge the enthusiastic encouragement of Dr Ugo Carraro and the help of Prof. Stefano Schiaffino's group and of Dr Marcello Cantini for embryonic tissue isolation. The skillful technical assistance of Mr Silvio Belluco is also gratefully acknowledged. This work was supported in part by a grant of Muscular Dystrophy Association of America to Prof. Massimiliano Aloisi.     

Effect of platelet activating factor on guinea-pig papillary muscle

Platelet activating factor (PAF) induces a biphasic effect on guinea-pig papillary muscle: 1. a transient positive inotropic effect preceded by an increase in action potential duration (APD); 2. a marked negative effect on inotropism and on APD. Since Ca++ slow action potentials were initially enhanced by PAF and then markedly depressed, it is suggested that PAF specifically interferes with the Ca++ slow channel.     

Effect of platelet activating factor on guinea-pig papillary muscle

Summary Platelet activating factor (PAF) induces a biphasic effect on guinea-pig papillary muscle: 1. a transient positive inotropic effect preceded by an increase in action potential duration (APD); 2. a marked negative effect on inotropism and on APD. Since Ca⁺⁺ slow action potentials were initially enhanced by PAF and then markedly depressed, it is suggested that PAF specifically interferes with the Ca⁺⁺ slow channel.     

Syncoilin, an intermediate filament-like protein linked to the dystrophin associated protein complex in skeletal muscle

Syncoilin is a member of the intermediate filament protein family, highly expressed in skeletal and cardiac muscle. Syncoilin binds α-dystrobrevin, a component of the dystrophin associated protein complex (DAPC) located at the muscle cell membrane, and desmin, a muscle-specific intermediate filament protein, thus providing a link between the DAPC and the muscle intermediate filament network. This link may be important for muscle integrity and force transduction during contraction, a theory that is supported by the reduced force-generating capacity of muscles from syncoilin-null mice. Additionally, syncoilin is found at increased levels in the regenerating muscle fibres of patients with muscular dystrophies and mouse models of muscle disease. Therefore, syncoilin may be important for muscle regeneration in response to injury. The aims of this article are to review current knowledge about syncoilin and to discuss its possible functions in skeletal muscle. Received 21 May 2008; received after revision 10 July 2008; accepted 18 July 2008     

Electromyographic responses elicited by cutaneous and mixed nerve stimulation in human tibialis anterior muscle

The rectified and averaged myoelectrical responses of the anterior tibial muscle to stimulation of the posterior tibial, peroneal and sural nerves at the ankle were recorded during a weak isometric contraction in man. The stimulation of the posterior tibial nerve elicited two excitatory phases (short and long latency excitations) at 40 ms and 78 ms latencies, respectively, separated by a phase of reduced activity. With peroneal and sural nerve stimulation such triphasic responses were less consistent; only a monophasic inhibitory response occurred in some recordings. These results indicate that well-identifiable responses with distinct latencies can be obtained in human leg muscle with cutaneous and mixed nerve stimulation distal to the muscle.     

Electromyographic responses elicited by cutaneous and mixed nerve stimulation in human tibialis anterior muscle

Summary The rectified and averaged myoelectrical responses of the anterior tibial muscle to stimulation of the posterior tibial, peroneal and sural nerves at the ankle were recorded during a weak isometric contraction in man. The stimulation of the posterior tibial nerve elicited two excitatory phases (short and long latency excitations) at 40 ms and 78 ms latencies, respectively, separated by a phase of reduced activity. With peroneal and sural nerve stimulation such triphasic responses were less consistent; only a monophasic inhibitory response occurred in some recordings. These results indicate that well-identifiable responses with distinct latencies can be obtained in human leg muscle with cutaneous and mixed nerve stimulation distal to the muscle.This work was supported by the Council of Physical Education and Sport (Ministry of Education), Finland.     

Changes in cholinesterase activity of muscle after crushing the sciatic nerve of rats

The subcellular distribution of cholinesterase (ChE) was studied in the gastrocnemius muscle of rats after strong or weak nerve crushing. The ChE activities of muscle were decreased to a greater extent by strong crushing than by weak crushing. In particular, the ChE activity of the fraction containing sarcoplasmic reticulum was most greatly decreased. These results suggest that the change in the ChE activity of the microsomal fraction most finely reflects the strength of nerve crushing.     

Endogenous oscillatory activity and TTX-sensitive spikes of the heart muscle in early juveniles of the isopod crustaceanLigia exotica

The heart beat of early juveniles of the littoral isopodLigia exotica occurred at a frequency of 250 to 350/min, associated with rhythmic activity of the heart muscle. Each burst was composed of a slow depolarizing potential with superimposed spike potentials. The spike potential was eliminated by perfusion with TTX-containing or Na⁺-free saline. In TTX-saline, the slow potential was unchanged in frequency and amplitude. By current injection into the heart muscle, the rhythm of the slow potential was phase-shifted and its frequency was changed in a membrane potential-dependent manner. These results show that the heart ofLigia early juveniles acts as an endogenous muscle oscillator generating oscillatory slow potentials and Na⁺-dependent spikes.     

Effects of disuse and nerve stump length on the development of fibrillation in denervated soleus muscle

Summary Both 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 than following the proximal one.     

Mitochondrial network remodeling: an important feature of myogenesis and skeletal muscle regeneration

The remodeling of the mitochondrial network is a critical process in maintaining cellular homeostasis and is intimately related to mitochondrial function. The interplay between the formation of new mitochondria (biogenesis) and the removal of damaged mitochondria (mitophagy) provide a means for the repopulation of the mitochondrial network. Additionally, mitochondrial fission and fusion serve as a bridge between biogenesis and mitophagy. In recent years, the importance of these processes has been characterised in multiple tissue- and cell-types, and under various conditions. In skeletal muscle, the robust remodeling of the mitochondrial network is observed, particularly after injury where large portions of the tissue/cell structures are damaged. The significance of mitochondrial remodeling in regulating skeletal muscle regeneration has been widely studied, with alterations in mitochondrial remodeling processes leading to incomplete regeneration and impaired skeletal muscle function. Needless to say, important questions related to mitochondrial remodeling and skeletal muscle regeneration still remain unanswered and require further investigation. Therefore, this review will discuss the known molecular mechanisms of mitochondrial network remodeling, as well as integrate these mechanisms and discuss their relevance in myogenesis and regenerating skeletal muscle.

     

Effect of nerve stimulation on rat skeletal muscle. A study of plasma membrane

The gastrocnemius muscle of the rat showed no morphological, histometric or plasma membrane changes, after sciatic nerve stimulation with a 5mA current for 30 to 60 min, 10 mA for 30 min and 15 mA for 5 min. However, 10 mA for 60 and 200 min gave rise to mitochondrial and plasma membrane abnormalities. These changes were absent after a rest period. The results indicated that the sciatic nerve stimulation at 10 mA for 60 and 200 min caused reversible changes in the rat skeletal muscle mitochondria and plasma membrane.     

Myosin isoenzymes during in vivo and in vitro differentiation of chick muscles

Muscle fibers differentiated, in vitro, from myoblasts of embryonic Pectoralis (presumptive fast) and embryonic Adductor magnus (presumptive slow) muscles synthesise the same type of myosin, which is identical to the type synthesised in day 10 embryonic muscles. This type of myosin comigrates with the third isozyme of the adult fast-twitch muscle. There is no change in the kind of myosin in cultures aged from 2 to 7 weeks, whereas during the in vivo differentiation of the same muscles, new isozymes appear which are different in the two muscles. With regard to myosin, the muscle fibers differentiated, in vitro, from myoblasts of fast or slow muscles expressed the same phenotype.     

Changes in cholinesterase activity of muscle after crushing the sciatic nerve of rats

Summary The subcellular distribution of cholinesterase (ChE) was studied in the gastrocnemius muscle of rats after strong or weak nerve crushing. The ChE activities of muscle were decreased to a greater extent by strong crushing than by weak crushing. In particular, the ChE activity of the fraction containing sarcoplasmic reticulum was most greatly decreased. These results suggest that the change in the ChE activity of the microsomal fraction most finely reflects the strength of nerve crushing.Acknowledgments. This study was accomplished in Central Research Laboratories, Sankyo Co. Ltd. The authors wish to thank Prof. Tsuneyuki Nakazawa, Department of Neuropsychiatry, School of Medicine, Fujita-Gakuen University, and Dr Yutaka Sakai for their valuable advice and support, Sr Jean M. Michalec for her critical comments, and Miss Hamako Katano, Mr Naoji Mikuni and Miss Yoshie Ishii for their skillful technical assistance.     

Some ultrastructural observations on the denervated skeletal muscle of frog

Summary The frog skeletal muscle resists atrophy for a long time after denervation. If, however, the entry of the nerve is prevented for more than 3.5 months, small muscle portions, sometimes containing nucleus, are sequestered from the parent muscle fibre. The basal lamina does not dissociate from these detached muscle portions.     

Do peripheral nerves contain a factor inducing acetylcholine sensitivity in skeletal muscle?

A crude extract of the sciatic nerve, eluate of dialyzed nerve extract or 2 folin-positive sephadex fractions induced acetylcholine sensitivity of extrajunctional regions in extensor digitorum longus muscle fibres of the rat, when released from silastic plates implanted for 3--4 days onto the muscle surface.     

Geschwindigkeit der Nervenleitung innerhalb der Netzhaut

Summary The conduction velocity of the unmyelinated portion of the optic nerve fibres within the cat's retina was measured by shifting a microelectrode from the blind spot outwards and stimulating antidromically in the lateral geniculate body. The mean conduction velocities were 2.8 m/s for the fast, and 1.7 m/s for the slow group of optic nerve fibres, as compared with maxima of 70 and 23 m/s respectively for the same groups in the myelinated extrabulbar portion.     

Coordinated activation of muscle fibres by different conduction velocities in branches of a crustacean motor axon

Summary Higher conduction velocities in branches of the fast excitor axon to distal muscle fibres ensure that these fibres are activated almost simultaneously with proximal fibres in the claw closer muscle of lobsters, producing a contraction of maximal force.Supported by Muscular Dystrophy Association and National Research Council of Canada.Supported by National Institute of Health and Muscular Dystrophy Association of America.     

Some ultrastructural observations on the denervated skeletal muscle of frog.

The frog skeletal muscle resists atrophy for a long time after denervation. If, however, the entry of the nerve is prevented for more than 3.5 months, small muscle portions, sometimes containing nucleus, are sequestered from the parent muscle fibre. The basal lamina does not dissociate from these detached muscle portions.