Ischemia-induced increase of stiffness of αB-crystallin/HSPB2-deficient myocardium

The two small heat shock proteins (sHSPs), B-crystallin and HSPB2, have been shown to translocate within a few minutes of cardiac ischemia from the cytosol to myofibrils; and it has been suggested that their chaperone-like properties might protect myofibrillar proteins from unfolding or aggregation during stress conditions. Further evidence of an important role for HSPs in muscle function is provided by the fact that mutations of the B-crystallin gene cause myopathy and cardiomyopathy. In the present study, we subjected isolated papillary muscles of B-crystallin/HSPB2-deficient mice to simulated ischemia and reperfusion. During ischemia in B-crystallin/HSPB2-deficient muscles, the development of contracture started earlier and reached a higher value compared to the wildtype mice. The recovery of contracture of B-crystallin/HSPB2-deficient muscles was also attenuated during the simulated reperfusion period. However, twitch force was not significantly altered at any time of the experiment. This suggests that during ischemic insults, B-crystallin/HSPB2 may not be important for the contraction process itself, but rather serve to maintain muscular elasticity.     

Activation of the skeletal α-actin promoter during muscle regeneration

Little is known conerning promoter regulation of genes in regenerating skeletal muscles. In young rats, recovery of muscle mass and protein content is complete within 21 days. During the initial 5–10 days of regeneration, mRNA abundance for IGF-I, myogenin and MyoD have been shown to be dramatically increased. The skeletal -actin promoter contains E box and serum response element (SRE) regulatory regions which are directly or indirectly activated by myogenin (or MyoD) and IGF-I proteins, respectively. We hypothesized that the skeletal -actin promoter activity would increase during muscle regeneration, and that this induction would occur before muscle protein content returned to normal. Total protein content and the percentage content of skeletal -actin protein was diminished at 4 and 8 days and re-accumulation had largely occurred by 16 days post-bupivacaine injection. Skeletal - actin mRNA per whole muscle was decreased at day 8, and thereafter returned to control values. During regeneration at day 8, luciferase activity (a reporter of promoter activity) directed by –424 skeletal -actin and –99 skeletal -actin promoter constructs was increased by 700% and 250% respectively; however, at day 16, skeletal -actin promoter activities were similar to control values. Thus, initial activation of the skeletal - actin promoter is associated with regeneration of skeletal muscle, despite not being sustained during the later stages of regrowth. The proximal SRE of the skeletal -actin promoter was not sufficient to confer a regeneration-induced promoter activation, despite increased serum response factor protein binding to this regulatory element in electrophoretic mobility shift assays. Skeletal -actin promoter induction during regeneration is due to a combination of regulatory elements, at least including the SRE and E box. © Kluwer Academic Publishers.     

Activation of locomotor and grasping spine muscle fibres in chaetognaths: a curious paradox

Chaetognath muscle fibres resemble vertebrate muscle fibres in having an abundant sarcoplasmic reticulum (SR) and analogues of the transverse (T) tubular system, but contraction is regulated differently. In intact chaetognaths electrically-evoked contractions of the striated locomotor muscles were largely or totally blocked by d-tubocurarine, by surgical removal of the ventral ganglion and by Co²⁺. Contractions of single cells enzymatically dissociated from locomotor muscles were likewise blocked by Co²⁺, they twitched once only after calciseptine, showed neither contractures nor elevated intracellular Ca²⁺ with caffeine, and ryanodine did not block contractions. Whole cell voltage-clamped locomotor muscle cells displayed a typical inward rectified Ca²⁺ current that was sensitive to the Ca²⁺ channel blockers nifedipine and calciseptine and showed voltage-dependent activation with a threshold at –25 mV and a peak inward current at + 10 mV. In contrast, whole cell voltage-clamped cells from the muscles operating the grasping spines of the head showed an initial very rapid and rapidly-inactivating inward current abolished by tetrodotoxin (TTX), followed by a slower and slowly-inactivating inward current blocked by calciseptine. The relation between these observations and the unusual vertebrate-like structure of the muscle cells is discussed.     

Anticipatory postural changes induced by active unloading and comparison with passive unloading in man

Normal human subjects, sitting in a chair, were required to maintain stable elbow flexion against loads of 0.5 kg or 1.0 kg. Unloading was affected either passively by the experimenter, or actively with the subject's own contralateral arm. Elbow angle, force exerted by the load, and electromyographic activity (EMG) of biceps and triceps muscles of both arms were recorded and averaged. Passive unloading was followed by a reduction of biceps EMG activity, starting 50–80 ms after weight lift, and by an upward deflection of the forearm. With active unloading, however, a reduction of the biceps EMG activity slightly preceded the onset of unloading (0–30 ms). This reduction of the actively unloaded arm occurred at about the same time as the activity of the contralateral unloading arm. In this experiment, the unloaded forearm maintained an almost stable position. Thus, the anticipatory adjustment of elbow posture, observed when unloading was performed by the subject, appears to optimize limb stability during the mechanical perturbation.     

α and β glucocorticoid receptor mRNA expressionin skeletal muscle

The aim of the present study was to investigate the occurrence and autoregulation of both glucocorticoid receptor mRNAs in rat gastrocnemius muscle. The expression of both receptor forms was studied 1, 4 or 12hours after intra-tracheal instillation of a high dose (100g) of budesonide; muscular expression was compared with glucocorticoid receptor expression in lung tissue. After Northern blot analysis, hybridization was performed with glucocorticoid receptor, glyceraldehyde-3-phosphate dehydrogenase and glutamine synthetase probes. In the gastrocnemius muscle, both the and glucocorticoid receptor mRNA forms were detected and found to be downregulated four hours after the budesonide instillation. / glucocorticoid receptor ratios were lower in the gastrocnemius (1.1±0.2) than in the lungs (2.6±0.6). In the lungs, at all time points, the average glucocorticoid receptor mRNA levels did not differ from controls, although glutamine synthetase mRNA levels were upregulated. The glucocorticoid receptor mRNA was slightly reduced at 1 and 4hours. In conclusion, after intra-tracheal instillation of budesonide, both and glucocorticoid receptor forms were downregulated in muscle tissue. The difference in / glucocorticoid receptor mRNA ratios and concentrations between lung and gastrocnemius muscle supports the hypothesis of differential gene regulation by glucocorticoids in different cell types. © Kluwer Academic Publishers.     

The ‘catch’ mechanism in molluscan muscle: an electron microscopy study of freeze-substituted anterior byssus retractor muscle ofMytilus edulis

Summary A method for quick-freezing muscles while observing their mechanical properties until the moment of freezing is described. This method was used to freeze the anterior byssus retractor muscle (ABRM) ofMytilus edulis. Intact muscle in the presence of sucrose as a cryoprotectant was freeze-substituted in acetone, fixed and embedded for electron microscopy. ABRM was frozen in a number of mechanical states including catch, the state of high passive tension particularly associated with some molluscan muscles. Transverse sections were examined to determine the distribution of filaments in the muscle cells. In the relaxed muscle thick and thin filaments are fairly randomly distributed. Groups of thin filaments and of thick filaments are often seen, and there is no obvious association between the two types of filaments. In contrast, in rigor muscles, both glycerol-extracted and intact, most of the thin filaments were found to lie in rings or rosettes around the thick filaments. In some places bridges between thick and thin filaments could be distinguished. In actively contracting muscle (phasic contraction) the appearance is intermediate between that of the relaxed and rigor muscles. Many thick filaments are surrounded by rosettes of thin filaments but many of the thin filaments are grouped and have no connections with thick filaments. The catch state, left after a period of tonic contraction, is similar in its distributrion of thick and thin filaments to the active state, many of the thin filaments lying between the thick. Frequently thick and thin filaments seem to be closer together than in other states of the muscle where a pronounced exclusion zone is present around the thick filaments. There is no evidence for association between the thick filaments.The different distribution of thin filaments in the different states is consistent with the previously described X-ray diffraction data if it is assumed that most of the contribution to the equatorial reflection at 12 nm comes from the groups of thin filaments. Our data support a model for catch in which there is a change in the association between thick and thin filaments, rather than one in which thick filaments are clumped.     

A comparative immunohistological study of cerebellar enolases

Summary A comparative immunohistological study of the neurone-specific enolase and enolase, demonstrates the exclusive neuronal localization of enolase and its absence from glial cells. In contrast, enolase is located in astroglial cells. The validity of enolase as a neuronal marker and enolase as an astrocytic marker, is confirmed both by a double labelling technique, using antibodies to and to revealed with fluorescence or peroxidase in the same tissue sections, and by immunoelectronmicroscopy.     

Antigenic similarity between the protein neurotoxin α-bungarotoxin and neuromuscular blocking drugs

The snake neurotoxins -bungarotoxin (-BGT) and -bungarotoxin (-BGT) which act at the neuromuscular junction, were found to bind to IgE antibodies directed against neuromuscular blocking (NMB) drugs in the sera of two patients who had experienced lifethreatening anaphylactic reactions to succinylcholine. -BGT inhibited IgE-binding to a choline-Sepharose solid support in one patient better than the NMB drug alcuronium, choline, triethylcholine and -BGT. IC₅₀s for -BGT and succinylcholine were 16 and 10 nmol respectively for one patient and 34 and 6.0 nmol for the other.Recognition of the NMB drugs and -BGT by the same antibody is the first demonstration of an antigenic similarity between these drugs and the protein toxin.     

Effect of muscle length on surface EMG wave forms in isometric contractions

Summary To elucidate the influence of muscle length on surface EMG wave form, comparisons were made of surface EMGs of the biceps and triceps brachii muscles during isometric contractions at different muscle lengths. Muscle lengths were altered by setting the elbow joint angle at several intervals between the limits of extension and flexion. The intensity of the isometric contractions was 25% of maximum voluntary contraction at the individual joint angles. Slowing was obvious in the EMG wave forms of biceps as muscle length increased. The so-called Piper rhythm appeared when the muscle was more than moderately lengthened. The slowing trend with muscle lengthening, though less marked, was also seen in triceps. Zero-cross analysis revealed quasi-linear relationships between muscle length and slowing. Frequency analysis confirmed the development of Piper rhythm. An attempt was made to interpret the slowing associated with muscle lengthening in terms of the propagation of myoelectric signals in muscle fibers. Given the effect of muscle length on EMG wave forms, a careful control of joint angle may be required in assessing local muscle fatigue when using EMG spectral indices.     

Lack of myoblasts migration between transplanted and host muscles of mdx and normal mice

Summary Extensor digitorum longus muscles of normal mice (C57BL/10ScSn hereafter called C57) were orthotopically transplanted into dystrophin-deficient mice (mdx) and reciprocally, mdx Extensor digitorum longus muscles were transplanted into C57 mice. After an initial phase of degeneration, transplanted muscles regenerate nearly completely, as evaluated from the maximum isometric force of muscles isolated 60 days after the surgery. In other similar experiments, instead of isolating the grafted muscles, we excised the antero-external muscles of the leg, including the grafted muscle. Cryostat cross-sections at three levels along the muscles were immunostained with an anti-dystrophin antibody. No muscle cells of dystrophin-deficient muscles grafted into normal mice took the antibody except a few revertant fibres, while all the muscle cells of the normal host were immunostained. Reciprocally, all the muscles cells of normal grafts were stained, whilst no antibody stained the cells of the surrounding muscles of the dystrophin-deficient host. These experiments show that very few if any of the myoblasts or muscle precursor cells, active during the regeneration of grafted muscle, migrate into the adjacent muscles. These results could be explained by the absence, in our work, of injuries of the grafted and adjacent host muscles epimysium and the absence of extensive inflammatory reactions. This lack of myoblast mobility suggest that when myoblast transfer is applied to muscle therapy, it will be necessary to inject myoblasts within each muscle to obtain an efficient treatment.     

Neural and Mechanical Contributions to the Stretch Reflex: A Model Synthesis

A model for the soleus stretch reflex in the decerebrate cat was synthesized from models of the neural and muscular components, including the two proprioceptors (the muscle spindle and Golgi tendon organ) and their associated afferents (Ia, II, and Ib), the motoneuron pool with its reflex pathways, the branches of the motoneurons to the intrafusal muscles ( innervation), and the extrafusal muscle. Parameters for the muscle and receptor models were chosen independently to match their responses in isolation. Reflex gains and inputs were estimated to fit the response to stretch measured by Nichols and Houk. The chosen reflex gains and inputs are not unique; many different combinations reproduced the characteristic stretch response. With a single set of fixed parameters, the model predicted many mechanical properties of the stretch reflex, including linearization effects (when the stretch magnitude and direction are varied), as well as the dependence on operating force and initial muscle length. The model did not accurately predict the responses at higher stretch velocities, due to failure of the extrafusal muscle model. © 2002 Biomedical Engineering Society. PAC02: 8719Ff, 8719Rr, 8719La     

Activity in torso muscles during relaxed standing

Summary Electromyographic activity of erector spinae, external oblique, and rectus abdominis muscles was studied during relaxed standing compared to lying down. Activity in the forearm extensors and forearm flexors was also studied. Surface electrodes were used.Each of the torso muscles exhibited 0.2 V of activity and the forearm muscles 0.1 V while subjects were relaxed and lying down. During quiet standing the erector spinae, external oblique, and rectus abdominis muscles showed a median activity of 1.0 V, 2.5 V, and 0.7 V respectively (for a minimum of ten 10-sec samples per subject). Examination of the integrated records during standing revealed no periods without increased muscle activity in the torso muscles. By contrast, activity in the forearm muscles did not increase during standing.The major superficial muscles of posture in the torso appear to act as guy wires, being continually active during standing. There is no support for hypotheses of passive support for the torso, nor do torso muscles act in either/or fashion; both anterior and posterior muscles are active at once. There is no sign of generally increased muscle tone in all muscles or in extensors; only the postural muscles are continuously active.     

Translation enhancer in the 3′-untranslated region of rotavirus gene 6 mRNA promotes expression of the major capsid protein VP6

Summary. The eleven rotavirus mRNAs contain 5-cap structures and most end with the 3-consensus sequence 5-UGACC-3. The UGACC functions as a common translation enhancer (3-TE-con) that upregulates viral protein expression through a process mediated by the nonstructural protein NSP3. To address the possibility that gene-specific enhancers are also contained in the untranslated regions (UTRs) of the rotavirus mRNAs, we used rabbit reticulocyte lysates to investigate the translation efficiencies of analog RNAs containing viral-specific 5-and 3-UTRs and the open reading frame for chloramphenicol acetyltransferase. These experiments combined with the analysis of full-length viral RNAs and RNAs containing 3-truncations showed that a highly active enhancer was present near the 5-end of the 139-nucleotide 3-UTR of the gene 6 mRNA (3-TEg6). The 3-TEg6 represents a functionally independent enhancer, as no other portion of the gene 6 mRNA was required for its activity. The 3-TEg6 differs significantly from the 3-TE-con in that the gene 6-specific enhancer does not require viral protein for activity and is formed by a sequence unique to only one of the eleven viral mRNAs. Together, our findings suggest that the 3-UTR of the gene 6 mRNA contains two TEs, one is gene-specific (3-TEg6) and the other is common to nearly all rotavirus genes (3-TE-con). The activity of the 3-TEg6 is likely important for directing the efficient translation of the gene 6 mRNA at levels sufficient to provide the 780 copies of VP6 necessary for the assembly of each progeny virion.     

Structurally differentDrosophila striated muscles utilize distinct variants of Z-band-associated proteins

Summary Monoclonal antibodies raised against four proteins from insect asynchronous flight muscle have been used to characterize the cross-reacting proteins in synchronous muscle ofDrosophila melanogaster. Two proteins,-actinin and Z(400/600), are found at the Z-band of every muscle examined. A larger variant of-actinin is specific for the perforated Z-bands of supercontractile muscle. A third Z-band protein, Z(210), has a very limited distribution. It is found only in the asynchronous muscle and in the large cells of the jump muscle (tergal depressor of the trochanter). The absence of Z(210) from the anterior four small cells of the jump muscle demonstrates that cells within the same muscle do not have identical Z-band composition. The fourth protein, projectin, > 600 kDa polypeptide component of the connecting filaments in asynchronous muscle, is also detected in all synchronous muscles studied. Surprisingly, projectin is detected in the region of the thick filaments in synchronous muscles, rather than between the thick filaments and the Z-band, as in asynchronous muscles. Despite their different locations, the projectins of synchronous and asynchronous muscles are very similar, but not identical, as judged by SDS-PAGE and by peptide mapping. Projectin shows immunological cross-reactivity with twitchin, a nematode giant protein that is a component of the body wall A-band and shares similarities with vertebrate titin.     

Postural adjustments due to external perturbations during sitting in 1-month-old infants: evidence for the innate origin of direction specificity

The aim of the study was to examine whether infants, at an age when they have no or little experience in sitting, can produce direction specific postural adjustments, i.e. synergies of muscle activity on the ventral side of the body during backward sway and on the dorsal side during forward sway. In addition, we addressed the question whether postural adjustments at this young age are restricted to single muscle responses or consist of a variable repertoire of muscle activation patterns including one during which all direction specific muscles participate (complete pattern). Postural adjustments due to external perturbations in a sitting position were studied in eight healthy infants aged 1 month. Multiple surface EMGs of neck, trunk and leg muscles and kinematics were recorded while the infants were exposed to horizontal forward (Fw) and backward (Bw) displacements of the surface of support. Direction specific postural adjustments, defined as adjustments during which agonist activation or antagonist inhibition preceded antagonist activation, were present in 85% of Bw and 72% of Fw translations. The direction specific adjustments showed a large variability with the repertoire of adjustments including the activation of one, two or all of the recorded direction specific muscles. The finding of direction specific adjustments at 1 month of age support the opinion that the basic level of organisation of postural adjustments has an innate origin. The finding of a variable repertoire of muscle response patterns, including the complete pattern, refutes the idea that the development of postural adjustments results from gradual addition of appropriate muscles to the synergies.Electronic Supplementary Material Electronic supplementary material is available in the online version of this article at The study was supported financially by Folke Bernadotte Stiftelsen, Linnéa och Josef Carlssons Stiftelse, Norrbacka-Eugeniastiftelsen, Riksförbundet för Rörelsehindrade Barn och Ungdomar and Sunnerdahls Handikappfond     

Fish muscle structure: fibre types in flatfish and mullet fin muscles using histochemistry and antimyosin antibody labelling

Summary In studies of the myosin crossbridge interaction with actin in vertebrate muscles, the muscles of bony fish have the unique advantage for ultrastructural work that the A-band has a simple crystalline lattice of myosin filaments. However, the anatomy and physiology of these fish muscles is relatively poorly understood compared with the rabbit, chicken or frog muscles conventionally used for crossbridge studies. Here the fibre types in fish fin muscles have been characterized to allow sensible selection of single fish fibres for ultrastructural studies. The fibre type compositions of the fin muscles of mullet, plaice, sole and turbot were examined by histochemistry and immunohistochemistry using polyclonal antibodies raised against various myosin isoforms: fish slow, fish fast, mammalian fast (type IIA) and chicken tonic myosins. In the mullet, fin muscles were composed of variable proportions of fast and slow fibres. In the three flatfish, the fin muscle showed a zonal arrangement with slow fibres, binding anti-slow myosin antibody, next to the skin ( region). The bulk of the muscle, distal to the skin, was a typical fast muscle both histochemically and in its reaction with antibodies ( region). Between these two regions there may be one (sole) or two (turbot, plaice) intermediate zones ( and regions) comparable to the pink/intermediate layer of myotomal muscle. In the plaice fin muscle, two kinds of slow fibre could be distinguished immunohistochemically.     

Use of girth measurements for estimating body volume and body density in Indian girls aged 10–19 years

Summary Mean values and standard deviations of total body volume, body density, height, weight, and a battery of 20 girth measurements of 200 Punjabi girls aged 10–19 years are presented. Selective stepwise multiple regression equations for predicting total body volume and body density from girth measurements are also given for different age groups.Hip girth was the most commonly selected measurement at the first step in most age groups and the values of r between hip girth and total body volume ranged between 0.86–0.96 in different age groups. The values of multiple R between total body volume and a combination of first four selected girth measurements varied from 0.96–0.99 in different age groups.The values of multiple R between body density and a combination of four girth measurements selected up to fourth step ranged between 0.73–0.92 in different age groups.     

α-cardiac-like myosin heavy chain MHCIα is not upregulated in transforming rat muscle

The expression of MHCI, an -cardiac-like myosin heavy chain isoform, was studied in extensor digitorum longus (EDL) and tibialis anterior (TA) rat muscles undergoing fast-to-slow transition by chronic low-frequency stimulation (CLFS), a condition inducing a transient upregulation of MHCI in rabbit muscle. In order to enhance the transformation process, CLFS was applied to hypothyroid rats. mRNA analyses were performed by RT-PCR, and studies at the protein level by immunoblotting and immunohistochemistry, using the F88 antibody (F88 12F8,1) demonstrated in the accompanying paper to be specific for MHCI. In total RNA preparations from slow- and fast-twitch muscles, MHCI mRNA was present at minute levels, at least three orders of magnitude lower than in cardiac atrium. As verified immunohistochemically, MHCI is present only in intrafusal fibres of rat muscle. Moreover, MHCI is not expressed in extrafusal fibres and, contrary to the rabbit, was not upregulated at both the mRNA and protein levels by CLFS. These results support our notion of species-specific responses to CLFS. Another antibody reported to be specific to MHCI, BA-G5, was also investigated by immunoblot and immunohistochemical analyses. Its specificity could not be validated for skeletal muscles of the rat. BG-A5 was shown to cross-react with MHCIIb and MHCI. These results question an upregulation of MHCI in transforming rat muscles as reported in studies based on the use of this antibody.     

Suppressive regions in the visual receptive fields of single cells of the pigeon's optic tectum

Summary Intracellularly HRP-labelled cat hindlimb -motoneurones were reconstructed light microscopically from a series of 1 m or 2 m thick consecutive sections. The volume and surface area of the soma as well as the size of the very proximal part of the dendritic and axonal processes were estimated morphometrically. Similar measurements were also made on adjacent unlabelled neurons in the same series of sections. A close relation was found between the soma volume and surface area on one hand the combined cross-sectional area of the proximal dendrites and axon on the other. The combined axonal and dendritic bases occupied on the average 16% of the soma surface. The accuracy in using the diameters and cross-sectional area of the cell body as indirect estimates of soma volume and surface area was analyzed. Combined measurements in both the transversal and sagittal planes were then found to yield more satisfactory estimates then when the measurements were confined only to the transversal plane. Several different formulas using the soma axes for indirect calculations of the soma volume and surface area were compared with respect to the accuracy of the results.     

Rhythmic Photostimulation and the Number of α-Rhythm Dipoles in the Human Brain

The numbers of -rhythm equivalent current dipoles (ECD) arising in the human brain before and during rhythmic photostimulation at the -rhythm frequency was studied in six healthy adult subjects. Dipoles were calculated using a single-dipole model for the whole of the -range and three subranges by solution of inverse equations in a three-layer model of the head obtained by simultaneous use of EEG data and MRI tomograms of the subjects' heads. The number of apparent ECD was significantly associated with rhythmic photostimulation and depended on the phase of the -rhythm wave at which stimulation started and on the type of visual illusion (circle, spiral, grid) appearing during this time. The relationship between these data and the hypothetical wave process scanning the human visual cortex at the frequency of the -rhythm is discussed.