New insights into the passive force enhancement in skeletal muscles

The steady-state isometric force following active stretching of a muscle is always greater than the steady-state isometric force obtained in a purely isometric contraction at the same length. This phenomenon has been termed "residual force enhancement" and it is associated with an active and a passive component. The origin of these components remains a matter of scientific debate. The purpose of this work was to test the hypothesis that the passive component of the residual force enhancement is caused by a passive structural element. In order to achieve this purpose, single fibers (n=6) from the lumbrical muscles of frog (Rana pipiens) were isolated and attached to a force transducer and a motor that could produce computer-controlled length changes. The passive force enhancement was assessed for three experimental conditions: in a normal Ringer's solution, and after the addition of 5 and 15mM 2,3-butanedione monoxime (BDM) which inhibits force production in a dose-dependent manner. If our hypothesis was correct, one would expect the passive force enhancement to be unaffected following BDM application. However, we found that increasing concentrations of BDM decreased the isometric forces, increased the normalized residual force enhancement, and most importantly for this study, increased the passive force enhancement. Furthermore, BDM decreased the rate of force relaxation after deactivation following active stretching of fibers, passive stretching in the Ringer's and BDM conditions produced the same passive force-sarcomere length relationship, and passive force enhancement required activation and force production. These results led to the conclusion that the passive force enhancement cannot be caused by a structural component exclusively as had been assumed up to date, but must be associated, directly or indirectly, with cross-bridge attachments upon activation and the associated active force.     

Individuation and holistic processing of faces in rhesus monkeys

Despite considerable evidence that neural activity in monkeys reflects various aspects of face perception, relatively little is known about monkeys' face processing abilities. Two characteristics of face processing observed in humans are a subordinate-level entry point, here, the default recognition of faces at the subordinate, rather than basic, level of categorization, and holistic effects, i.e. perception of facial displays as an integrated whole. The present study used an adaptation paradigm to test whether untrained rhesus macaques (Macaca mulatta) display these hallmarks of face processing. In experiments 1 and 2, macaques showed greater rebound from adaptation to conspecific faces than to other animals at the individual or subordinate level. In experiment 3, exchanging only the bottom half of a monkey face produced greater rebound in aligned than in misaligned composites, indicating that for normal, aligned faces, the new bottom half may have influenced the perception of the whole face. Scan path analysis supported this assertion: during rebound, fixation to the unchanged eye region was renewed, but only for aligned stimuli. These experiments show that macaques naturally display the distinguishing characteristics of face processing seen in humans and provide the first clear demonstration that holistic information guides scan paths for conspecific faces.     

Vanadate stimulates D-glucose transport into sarcolemmal vesicles from rat skeletal muscles.

Vanadate is known to have various insulin-like actions including activation of D-glucose uptake into the skeletal muscle and adipose tissue. In this study, we examined the effect of orthovanadate on D-glucose uptake into sarcolemmal vesicles prepared from rat hind limb skeletal muscles. In the presence of 10 mM vanadate, the initial rate of D-glucose uptake into sarcolemmal vesicles was enhanced 4-5 times above the basal value. Half-maximal concentration for this effect of vanadate was 3 mM. The D-glucose uptake was also stimulated by metavanadate, but not by selenite, selenate, or molybdate. When vanadate was removed from the vesicles by dilution and centrifugation, D-glucose uptake into the vesicles returned to the basal level, indicating that the effect of vanadate was reversible. Saturation curves showed that the Vmax value for the D-glucose uptake was enhanced more than 4-fold by 10 mM vanadate. Therefore, the activation of D-glucose uptake was due, at least in part, to a large increase in the Vmax value. These results suggest that vanadate increases the intrinsic activity (turnover number) of skeletal muscle glucose transporters in a reversible manner.     

Glycogen phosphorylase of skeletal muscles

A review is given on the affinity modification of pyridoxal phosphate and AMP-binding sites as well as on the chemical modification of essential amino acid residues of phosphorylase (histidine residue of the substrate-binding site and cysteine residue of the coenzyme-binding site). The role of allosteric effectors (AMP and glucose-6-phosphate) and functionally important centers of the protein in conformational transitions of rabbit muscle phosphorylase b is discussed. The kinetic properties of rabbit and bovine muscle phosphorylase are compared. Bovine muscle phosphorylase is shown to be a partly phosphorylated form of the enzyme. Some peculiarities of the pH-dependence of kinetic behaviour of the hybrid form of the bovine muscle enzyme are discussed.     

Aging of human skeletal muscles

Normal aging in humans is associated with progressive decrease in skeletal muscle mass and strength (sarcopenia) which contributes to frailty and falls. The age associated changes in body composition result from lower levels of anabolic hormones, oxidative damage, neuromuscular alterations and a general decrease in muscle protein turnover. In this review we discuss the potential mechanisms and physical activity as prevention and treatment of sarcopenia.     

Regeneration of entire skeletal muscles

There are several experimental models for producing the regeneration of entire mammalian muscles. The most commonly used are mincing and free muscle grafting. Immediately after both mincing and grafting, the muscle is completely divorced from any connections with the host. To regenerate and become functional, the muscle must become reintegrated with the body of the host. The three major reintegrative phenomena--revascularization, reinnervation, and the reestablishment of tendon connections--are discussed in the context of muscle regeneration. The functional development of regenerating muscle closely resembles the normal ontogenetic pattern. Final functional differentiation of a regenerating muscle depends on the establishment of neuromuscular synapses.     

Ruthenium-red staining of skeletal and cardiac muscles

Summary The effects of ruthenium red (RR) on amphibian and mammalian skeletal muscles and mammalian myocardium were examined. In skeletal muscle cells, a discrete pattern of staining can be brought about within the lumina of the terminal cisternae (junctional sarcoplasmic reticulum [SR]) by sequential exposure to RR and OsO₄. After prolonged immersion in RR solution, formation of pentalaminar segments (zippering) occurs at various points along the longitudinal (network) SR tubules. Zippering can be elicited in skeletal SR at any stage of preparation prior to postfixation with OsO₄. By means of dispersive X-ray analysis, both ruthenium and osmium were seen to be deposited in skeletal muscle junctional SR, and ruthenium was detected in the myoplasm as well. In skeletal muscles whose T tubules were ruptured by exposure to glycerol, the pattern of SR staining and zippering resulting from ruthenium-osmium treatment was not affected. These findings indicate that RR is capable of passage across the sarcolemma of skeletal muscle and that this passage does not occur solely under conditions in which the plasma membrane is damaged. In contrast, RR does not opacify or modify any region of the SR of cardiac muscle. However, after this treatment, randomly distributed opaque bodies, composed of parallel lamellar structures, appear throughout the myocardial cells. A few of these bodies are associated with lipid droplets, but the rest are of unknown origin. The failure of the SR of cardiac muscle to stain after exposure to ruthenium dye (even though this material enters these cells) suggests that the chemical composition of cardiac SR is significantly different from that of skeletal muscle SR.Supported in part by PHS grant HL-11155 (to N.S.) and American Heart Grant-in-Aid 78-753 (to M.S.F.). The authors are grateful to Drs. David Harder and Lawrence Sellin for their assistance with the preparation of frog skeletal muscle, to Dr. S.K. Jirge for his helpful suggestions and discussions, and particularly to Dr. Kenneth R. Lawless and Ms. Ann Marshall of the Department of Materials Sciences, University of Virginia School of Engineering, and Col. John M. Brady of the United States Army Institute of Dental Research, Walter Reed Army Medical Center, for their help with, and for the use of, the X-ray analysis equipment     

Electrotransfer of human IL-1Ra into skeletal muscles reduces the incidence of murine collagen-induced arthritis

BACKGROUND: It has previously been demonstrated that high levels of gene expression in skeletal muscles can be achieved after direct in vivo electrotransfer of naked plasmid DNA. The purpose of this study is to examine the potential of in vivo electroporation of plasmid DNA encoding human IL-1Ra for the prevention of murine collagen-induced arthritis (CIA). METHODS: DBA/1 mice were injected in gastrocnemius muscles with plasmid DNA followed by in vivo electroporation. To uncover the optimum conditions of gene transfer, various electric field strengths and different amounts of plasmid DNA were applied. Calf muscles around the injected areas were investigated with histological methods for damage to muscle tissue. The levels of human IL-1Ra expression in the injected area and also in the serum were determined with ELISA for human IL-1Ra. Based on these data, the effects of electrotransfer of plasmid DNA were tested using the murine CIA model. DBA/1 mice were immunized with bovine collagen type II at the base of the tail. On day 21, mice were given a booster injection with the same antigen. Mice were divided into two groups on day 26. One group of mice received plasmid containing the IL-1Ra cDNA sequence, while control mice were given plasmid lacking the IL-1Ra coding sequence. The incidence of arthritis was evaluated by macroscopic analysis, histological analysis, and the levels of inflammatory cytokines. RESULTS: IL-1Ra expression increased as a function of the electrical field strength and the amount of DNA. 200 V/cm (eight pulses; 20 ms per pulse; 1 Hz) and 15 microg of plasmid DNA per mouse were found to be optimum for gene transfer. After in vivo electroporation, gene expression in both muscle and serum increased gradually, reaching a peak value on day 10. Significant levels of human IL-1Ra expression were maintained for 20 days. Macroscopic analysis showed that the onset of CIA was significantly inhibited by direct electrotransfer of plasmid DNA encoding human IL-1Ra. Histological analysis of knee joints showed that the incidence of arthritis in knee joints was also prevented. The levels of mouse IL-1beta and IL-12 in paws were significantly lower in the group treated with IL-1Ra than those in the control group. CONCLUSIONS: These results demonstrate that direct electrotransfer of plasmid containing the human IL-1Ra cDNA sequence to skeletal muscle can reduce the incidence of CIA in mice.     

Mucosubstances in the human skeletal muscles.

With histomchemical, and electronmicroscopic-histochemical methods two types of human skeletal muscle fibres were established. The first type of muscle fibres does not contain acidic mucosubstances. The staining reactions and cellulase digestion indicate that, the neutral polysaccharides are cellulose-like substances. The second type of fibres contains only acidic mucosubstances, hyaluronic acid and chondroitine sulphate. The author suggests that the mucosubstances have joint function. These polysaccharides contributed to the jointing both of myofibrils and sarcomers. The polysaccharides can be exhibited in the joint points of contractile elements. In mechanical injury this point became disintegrated.