Comparative trends in shortening velocity and force production in skeletal muscles

Skeletal muscles are diverse in their properties, with specific contractile characteristics being matched to particular functions. In this study, published values of contractile properties for >130 diverse skeletal muscles were analyzed to detect common elements that account for variability in shortening velocity and force production. Body mass was found to be a significant predictor of shortening velocity in terrestrial and flying animals, with smaller animals possessing faster muscles. Although previous studies of terrestrial mammals revealed similar trends, the current study indicates that this pattern is more universal than previously appreciated. In contrast, shortening velocity in muscles used for swimming and nonlocomotory functions is not significantly affected by body size. Although force production is more uniform than shortening velocity, a significant correlation with shortening velocity was detected in muscles used for locomotion, with faster muscles tending to produce more force. Overall, the contractile properties of skeletal muscles are conserved among phylogenic groups, but have been significantly influenced by other factors such as body size and mode of locomotion.     

Walking on inclines: how do desert ants monitor slope and step length

Background

In order to increase the weak database concerning the organogenesis of Acoela – a clade regarded by many as the earliest extant offshoot of Bilateria and thus of particular interest for studies concerning the evolution of animal bodyplans – we analyzed the development of the musculature of Symsagittifera roscoffensis using F-actin labelling, confocal laserscanning microscopy, and 3D reconstruction software.

Results

At 40% of development between egg deposition and hatching short subepidermal fibres form. Muscle fibre development in the anterior body half precedes myogenesis in the posterior half. At 42% of development a grid of outer circular and inner longitudinal muscles is present in the bodywall. New circular muscles either branch off from present fibres or form adjacent to existing ones. The number of circular muscles is higher than that of the longitudinal muscles throughout all life cycle stages. Diagonal, circular and longitudinal muscles are initially rare but their number increases with time. The ventral side bears U-shaped muscles around the mouth, which in addition is surrounded by a sphincter muscle. With the exception of the region of the statocyst, dorsoventral muscles are present along the entire body of juveniles and adults, while adults additionally exhibit radially oriented internal muscles in the anterior tip. Outer diagonal muscles are present at the dorsal anterior tip of the adult. In adult animals, the male gonopore with its associated sexual organs expresses distinct muscles. No specific statocyst muscles were found. The muscle mantles of the needle-shaped sagittocysts are situated along the lateral edges of the animal and in the posterior end close to the male gonopore. In both juveniles and adults, non-muscular filaments, which stain positively for F-actin, are associated with certain sensory cells outside the bodywall musculature.

Conclusion

Compared to the myoanatomy of other acoel taxa, Symsagittifera roscoffensis shows a very complex musculature. Although data on presumably basal acoel clades are still scarce, the information currently available suggests an elaborated musculature with longitudinal, circular and U-shaped muscles as being part of the ancestral acoel bodyplan, thus increasing the possibility that Urbilateria likewise had a relatively complicated muscular ground pattern.     

The functional morphology of the feeding appendages and gut of Hippolyte varians (Crustacea: Natantia)

The musculature of the feeding appendages are described and compared with those few early accounts of other Decapoda, particularly those of Pandalus danae and Astacus fluviatilis . While the musculature is very similar to that of the latter, the relative importance of the various muscles may differ markedly and a number of previously undescribed muscles have been found, while others present in Pandulus and Astacus are not present in Hippolyte . The alimentary canal is also described, together with its associated musculature. The function of the various appendages and the parts of the gut are described from observations of living specimens.     

Morphohistochemical and electrophysiological characteristics of the transverse striated muscles of the rabbit esophagus

A specific histochemical profile of the muscular tunic of the stomach has been revealed; its myons demonstrate a high succinate dehydrogenase and myofibrillar ATPase activity. Electrical activity of the oesophageal musculature has common features with biopotentials of the skeletal muscles and the smooth musculature of the stomach. The similiarity with the skeletal muscle biopotentials is evident as a peculiar spike activity, especially at the time of feeding. In electrograms of the striated oesophageal muscles slow waves are seen; they change at deprivation and feeding. Therefore, it is possible to compare them with the smooth musculature capable to generate slow waves.     

The fine structure of the drum muscles of the Tigerfish,Therapon jarbua,as compared with the trunk musculature

Summary The fibers of drum and trunk muscles of the Tigerfish, Therapon jarbua, differ greatly in diameter. The myofibrils of the trunk muscles are irregularly oriented, while those of the drum muscles are rolled into spiral or concentric bands. Both muscle types possess the sarcomere structure typical of cross-striated musculature. However, the myofibrils of the drum muscles differ greatly in sarcomere length and width from those in the trunk musculature. The trunk muscles contain few mitochondria, whereas in the drum muscles mitochondria are abundant. The sarcoplasmic reticulum (SR) of the drum muscles takes the form of elongated tubes in both the A and the I region; that of the trunk musculature consists of small vesicles. Of the two muscle types, the drum muscle contains more SR. With respect to the form of the T system, the trunk musculature is of the Z type and the drum muscles of the A-I type. The drum muscle displays a considerably greater number of motor endplates; these lack typical junctional folds and have mitochondria with very few cristae. No fat could be demonstrated in either the drum or the trunk muscles. However, the concentration of glycogen is higher in the drum muscle than in the musculature of the trunk.This work was accomplished with support from the Deutsche Forschungsgemeinschaft and is gratefully dedicated to Prof. R. Danneel on the occasion of his 75th birthday.     

Spatial organization of musculature in the Himasthla elongata cercaria (Trematoda: Echinostomatidae)

Somatic muscles (body-wall and "parenchyma" musculature), muscles of suckers, alimentary tract and excretory bladder of Himasthla elongata cercaria were investigated using fluorescent phalloidin labelling and confocal microscopy. The arrangement of body-wall muscles differs between the certain parts of cercarial body and appears to be the most complicated in the collar district. Among the body-wall musculature, we described U-shaped muscles, which have never been found previously in trematodes. Muscles of oral and ventral suckers are grouped into 6-7 independent layers. In some of those layers, they are arranged bilaterally, which contradicts the tradition to consider the sucker as radially symmetric.     

Mediolateral somitic origin of ribs and dermis determined by quail-chick chimeras

Somites are transient mesodermal structures giving rise to all skeletal muscles of the body, the axial skeleton and the dermis of the back. Somites arise from successive segmentation of the presomitic mesoderm (PSM). They appear first as epithelial spheres that rapidly differentiate into a ventral mesenchyme, the sclerotome, and a dorsal epithelial dermomyotome. The sclerotome gives rise to vertebrae and ribs while the dermomyotome is the source of all skeletal muscles and the dorsal dermis. Quail-chick fate mapping and diI-labeling experiments have demonstrated that the epithelial somite can be further subdivided into a medial and a lateral moiety. These two subdomains are derived from different regions of the primitive streak and give rise to different sets of muscles. The lateral somitic cells migrate to form the musculature of the limbs and body wall, known as the hypaxial muscles, while the medial somite gives rise to the vertebrae and the associated epaxial muscles. The respective contribution of the medial and lateral somitic compartments to the other somitic derivatives, namely the dermis and the ribs has not been addressed and therefore remains unknown. We have created quail-chick chimeras of either the medial or lateral part of the PSM to examine the origin of the dorsal dermis and the ribs. We demonstrate that the whole dorsal dermis and the proximal ribs exclusively originates from the medial somitic compartment, whereas the distal ribs derive from the lateral compartment.     

The role of mechanical forces on the patterning of the avian feather-bearing skin: A biomechanical analysis of the integumentary musculature in birds

The integumentary musculature of birds consists of three distinct components. The smooth musculature comprises feather and apterial muscles, which form a continuous musculo-elastic layer within the dermis. The feather muscles, which consistently include at least erectors and depressors, interconnect contour feathers within pterylae (i.e., feather tracts) along gridlines that are oriented diagonally to the longitudinal and transverse axes of the body. The apterial muscles interconnect pterylae by attaching to the contour feathers along their peripheries. The striated musculature is composed of individual subcutaneous muscles, most of which attach to contour feathers along the caudal periphery of pterylae A new integrative functional analysis of the integumentary musculature proposes how apterial muscles stabilize the pterylae and modulate the tension of the musculo-elastic layer, and how subcutaneous muscles provide the initial stimulus for erector muscles being able to ruffle the contour feathers within pterylae. It also shows how the arrangement of the contour feathers and integumentary muscles reflects the stresses and strains that act on the avian skin. These mechanical forces are in effect not only in the adult, especially during flight, but may also be active during feather morphogenesis. The avian integument with its complex structural organization may, therefore, represent an excellent model for analyzing the nature of interactions between the environment and genetic material. The predictions of our model are testable, and our study demonstrates the relevance of integrated analyses of complex organs as mechanically coherent systems for evolutionary and developmental biology.     

The fastest contracting muscles of nonmammalian vertebrates express only one isoform of the ryanodine receptor.

The skeletal muscles of chickens, frogs, and fish have been reported to express two isoforms (alpha and beta) of the sarcoplasmic reticulum calcium release channel (ryanodine receptor or RYR), while mammals express only one. We have studied patterns of RYR isoform expression in skeletal muscles from a variety of fish, reptiles, and birds with immunological techniques. Immunoblot analysis with a monoclonal antibody that recognizes both nonmammalian RYR isoforms and a polyclonal antibody specific to the alpha isoform show two key results: (a) two reptilian orders share with mammals the pattern of expressing only the alpha (skeletal) RYR isoform in skeletal muscle; and (b) certain functionally specialized muscles of fish and birds express only the alpha RYR isoforms. While both isoforms are expressed in the body musculature of fish and birds, the alpha isoform is expressed alone in extraocular muscles and swimbladder muscles. The appearance of the alpha RYR isoform alone in the extraocular muscles and a fast-contracting sonic muscle in fish (toadfish swimbladder muscle) provides evidence that this isoform is selectively expressed when rapid contraction is required. The functional and phylogenetic implications of expression of the alpha isoform alone are discussed in the context of the mechanism and evolution of excitation-contraction coupling.     

Ultrastructural localization of lectin receptors on the bone-marrow sinusoidal endothelium of the rat

The purpose of this study was to estimate the absolute and relative masses of the three types of skeletal muscle fibers in the total hindlimb of the male Sprague-Dawley rat (Rattus norvegicus). For six rats, total body mass was recorded and the following weights taken from dissection of one hindlimb: 32 individual major muscles or muscle parts, remaining skeletal musculature (small hip muscles and intrinsic foot muscles), bone, inguinal fat pad, and skin. The fibers from the 32 muscles or muscle parts (which constituted 98% of the hindlimb skeletal muscle mass) were classified from histochemistry as fast-twitch oxidative glycolytic (FOG), fast-twitch glycolytic (FG), or slow-twitch oxidative (SO), and their populations were determined. Fiber cross-sectional areas from the same muscles were measured with a digitizer. Mass of each of the fiber types within muscles and in the total hindlimb was then calculated from fiber-type population, fiber-type area, and muscle-mass data. Skeletal muscle made up 71% of the total hindlimb mass. Of this, 76% was occupied by FG fibers, 19% by FOG fibers, and 5% by SO fibers. Thus, the FG fiber type is clearly the predominant fiber type in the rat hindlimb in terms of muscle mass. Fiber-type mass data are compared with physiological (blood flow) and biochemical (succinate dehydrogenase activities) data for the muscles taken from previous studies, and it is demonstrated that these functional properties are closely related to the proportions of muscle mass composed of the various fiber types.     

The Musculature of <Emphasis Type="Italic">Testudinella patina</Emphasis> (Rotifera: Flosculariacea), Revealed with CLSM

The musculature of Testudinella patina was visualized using phalloidin-linked fluorescent dye by confocal laser scanning microscopy. The conspicuous broad retractors appear to be made up of five separate fibers, of which three anchor in the neck region whereas two extend into the corona. Besides the broad retractors, a total of five paired longitudinal retractors are present and all of them extend into the corona. Incomplete circular muscles are found in groups in the neck region and in the medial and posterior parts of the trunk. The foot musculature comprises eight thin ventral foot muscles and six thicker dorsal foot muscles that all extend from the foot basis to the distal part of the foot. At the basis of the foot, each of the dorsal foot muscles anchors on a smaller, S-shaped subterminal foot muscle. The foot musculature furthermore comprises one pair of paraterminal foot muscles that each anchors basally on a subterminal foot muscle, extends into the most proximal part of the foot and attaches on one of the dorsal foot muscles. The visceral musculature is composed of extremely delicate fibers and is restricted to an area around and posterior to the foot opening. The presence of incomplete circular muscles supports that these muscles are a basal trait for Rotifera, whereas the morphology of the broad retractors and foot muscles is much more specialized and may be autapomorphic for Testudinella or alternatively for this genus and its closest relatives. The present results stress that revealing muscles by staining may produce new information from even well-investigated species, and that this information may contribute to a better understanding of functional as well as phylogenetic aspects of rotifer biology.     

Myosin light chains of skeletal and cardiac muscles of ground squirrel Citillus undulatus in different periods of hibernation

The isoform composition of myosin light chains and the extent of their phosphorylation in skeletal and cardiac muscles of ground squirrel Citellus undulatus in different periods of hibernation were studied. Regulatory myosin light chains of skeletal muscles of hibernating ground squirrels were completely dephosphorylated, while 25% of these light chains in active animals were phosphorylated. During hibernation, a shift of isoform composition of essential and regulatory skeletal muscle myosin light chains toward slower isoforms was observed, which is evidenced by the data obtained on m. psoas and on the totality of all skeletal muscles. In the atrial myocardium of hibernating ground squirrels, ventricular myosin light chains 1 (up to 60%) were registered. In contrast, during arousal of ground squirrels, in ventricular myocardium the appearance of atrial myosin light chains 1 (up to 30%) was revealed. A possible role of posttranslation changes in myosin light chains and their isoform shifts in the hibernation scenario is discussed.     

Use of Drosophila mutants to investigate the effect of disuse on the maintenance of muscle

The effect of continued muscular inactivity and prolonged paralysis on the structure and function of muscles was investigated in Drosophila melanogaster. A number of flightless mutants was examined to see whether their flight muscles degenerated as a result of disuse. No sign of progressive deterioration was observed in any of these mutants. Further, by producing mosaic flies in which part of the body expressed the temperature-sensitive paralytic mutation shibire^ST139, reversible local paralysis was obtained, and maintained for prolonged periods. Flies in which parts of the leg or flight musculature had been paralysed for several days were examined; no effect of such inactivity on the structure and function of the muscles was observed in any of the flies. These results indicate that in Drosophila continued muscular inactivity does not result in extensive degeneration of the musculature.     

Musculature in sipunculan worms: ontogeny and ancestral states

SUMMARY Molecular phylogenetics suggests that the Sipuncula fall into the Annelida, although they are morphologically very distinct and lack segmentation. To understand the evolutionary transformations from the annelid to the sipunculan body plan, it is important to reconstruct the ancestral states within the respective clades at all life history stages. Here we reconstruct the ancestral states for the head/introvert retractor muscles and the body wall musculature in the Sipuncula using Bayesian statistics. In addition, we describe the ontogenetic transformations of the two muscle systems in four sipunculan species with different developmental modes, using F-actin staining with fluorescent-labeled phalloidin in conjunction with confocal laser scanning microscopy. All four species, which have smooth body wall musculature and less than the full set of four introvert retractor muscles as adults, go through developmental stages with four retractor muscles that are eventually reduced to a lower number in the adult. The circular and sometimes the longitudinal body wall musculature are split into bands that later transform into a smooth sheath. Our ancestral state reconstructions suggest with nearly 100% probability that the ancestral sipunculan had four introvert retractor muscles, longitudinal body wall musculature in bands and circular body wall musculature arranged as a smooth sheath. Species with crawling larvae have more strongly developed body wall musculature than those with swimming larvae. To interpret our findings in the context of annelid evolution, a more solid phylogenetic framework is needed for the entire group and more data on ontogenetic transformations of annelid musculature are desirable.     

Kinetics of smimming in some smooth-bodied polychaetes

The opheliids Amniotrypane and Armundiu have very small parapodia bearing few chaetae, and these are pressed back against the body when the animals swim; the archiannelid Polygordius lacks parapodia and chaetae. All three worms have smooth bodies and swim by retrograde sinusoidal movements in the same way as other long, narrow, smooth-bodied animals, unlike nereidiform polychaetes in which the parapodial beat provides the driving force and the body undulations travelin the same direction as that of locomotion.
The wavelength of the undulations is comparable to the body length of these smooth polychaetes and this generally results in pronounced yaw. The kinetics of swimming are similar to those observed in nematodes and the amphioxus, and these polychaetes have comparable structural and mechanical features. A thick cuticle containing a spiral fibre system and lacking circular body-wall muscles is comparable to the situation in some nematodes, but in these polychaetes transverse muscles antagonize the longitudinal muscles and may allow adjustment of the internal hydrostatic pressure-and hence the stiffness of the body-as in the notochord of amphioxus which has similar swimming characteristics.
Like amphioxus, these polychaetes leave and re-enter the substratum in which they live. The small archiannelid Protodrilus has a similar muscular anatomy to that in Polygordius , but has a thin cuticle without spiral fibres. Prorodrilus has not with certainty been observed to swim.     

Effect of insulin on anabolic processes and growth in hypothyroid rats at various age periods

Studies have been made on a possibility of compensation of growth retardation in hypothyroid rats by insulin. In 30-day rats, compensation is not complete, although hypothyroidism is less significant as compared to that in animals which received merkazolil together with insulin. Further administration of insulin to rats up to the 90th day, resulted in a significant increase in the growth rate of skeletal muscles, body mass, protein content of skeletal muscles, as well as glycogen content of the liver and skeletal muscles. Thyroid insufficiency may be compensated by insulin alone, i.e. without simultaneous administration of thyroid hormones.     

Mechanical energy costs of human movement: an approach to evaluating the transfer possibilities of two-joint muscles

Different methods of calculating the mechanical energy cost of a movement presented in the literature can give results differing by an order of magnitude. The assumptions made concerning the transfer of energy between different parts of the body are part of the problem. This investigation assesses the role of transfer in energy saving and specifically, the possibility of two-joint muscles reducing the mechanical energy cost of a movement compared to a system having one-joint muscles only. An algorithm was developed which recruited one-joint or both one- and two-joint muscles to supply the net joint moments. The work performed under these two conditions was then compared. It was found that activation of both one- and two-joint musculature reduced the mechanical work cost during walking by between 7 and 29% over that required by single-joint musculature alone. This investigation supports suggestions in the literature that one of the functions of two-joint musculature is to reduce the mechanical energy cost and probably the metabolic cost of movement.     

Lipid peroxidation and oxidative phosphorylation in the heart and skeletal muscles of chickens developing under conditions of short-term cooling

Studies have been made of the effects of short-term cooling of eggs at the second part of the incubation period on the intensity of oxidative phosphorylation and peroxidative oxidation of lipids in the mitochondria of skeletal muscles and heart from the developing chicks. It was shown that the intensity of respiration and phosphorylation increases in both tissues, being more significant in skeletal muscles. It is suggested that activation of peroxidative oxidation of lipids at the background of the increasing oxygen consumption and phosphate esterification during adaptation of animals to changes in the environment is one of the mechanisms accounting for the compensatory changes in fatty acid composition of lipids.