RELEVANCE OF GENETIC ANIMAL MODELS OF MUSCULAR DYSTROPHY TO HUMAN MUSCULAR DYSTROPHIES

Age-related changes and tissue distribution of parvalbumin in normal and dystrophic mice of strain 129 ReJ

In murine muscular dystrophy, hindlimb muscle contains a functionally defective thiol protease inhibitor (TPI) which has been implicated in the onset and progression of the disease in mice. More recently, this protease inhibitor has been identified as parvalbumin, a calcium binding protein. In this study, a polyclonal antibody against mouse muscle parvalbumin was used to study the concentration and distribution of this protein in normal and dystrophic male mice at various ages. Immunodetection assays were used to screen extracts of hindlimb, forelimb, brain, heart, lung, liver, and kidney in 60-day-old normal and dystrophic male mice for parvalbumin content. Parvalbumin was detected in relatively high amounts in both hindlimb and forelimb muscle extracts, while much lower concentrations were detected in brains of normal and dystrophic animals. No parvalbumin was detected in the lung, liver, heart, or kidney extracts using the immunoassay. With aging, the parvalbumin concentration in hindlimb muscle of normal mice remained fairly constant for 90 days, whereupon the level increased at 120 days. In contrast, the parvalbumin concentration in hindlimb muscle of dystrophic mice decreased steadily with age to about 22%% of normal animals at 120 days. The parvalbumin content was also reduced in dystrophic brain.

In vivo T1 characterization of genetically induced muscle atrophy

In vivo spin-lattice relaxation times, T1, of water and lipid protons of normal and atrophic muscles were measured, using the spatially resolved spectroscopy (SPARS) sequence, in a genetic avian model of myopathy. These T1 values were compared with those of the hypertrophic muscles. Although the water T1 values of muscles were elevated in both types of lesions, the atrophic muscles showed a greater increase (54%) than the hypertrophic muscles (22%). The water T1 differentiation between the atrophic and hypertrophic muscles appeared to depend upon their bound water fractions that were calculated on the basis of the Fast Proton Diffusion model. The lipid T1 values of muscles were higher in the atrophic line of chickens compared to their genetic controls. In contrast, the lipid T1 values of muscles of the hypertrophic chickens and their controls were essentially identical. This suggests that the lipid T1 values may potentially complement the water T1 values in the differential diagnosis of muscle disorders.

Intracellular calcium in canine muscle biopsies

Intracellular staining for calcium was studied in muscle biopsies from 15 dogs by the alizarin red S (ARS) stain. Rare positive fibres were present in normal muscle and in denervation atrophy. The percentage of positive fibres was slightly increased in polymyositis, dermatomyositis and canine temporal/masseter myositis and markedly increased in progressive muscular dystrophy. Calcium-positive fibres were usually so-called large-dark (hypercontracted) fibres or necrotic fibres, although there was occasional staining of normal and atrophied fibres. These results indicate the probable involvement of calcium in muscle injury in canine inflammatory myopathies and in canine muscular dystrophy. In addition, use of the ARS stain appears to be useful for detecting the earliest lesions of acute muscle fibre injury.

Oxidative stress and muscular dystrophy

Oxidative stress may be the fundamental basis of many of the structural, functional and biochemical changes characteristic of the inherited muscular dystrophies in animals and humans. The presence of by-products of oxidative damage, and the compensatory increases in cellular antioxidants, both indicate oxidative stress may be occurring in dystrophic muscle. Changes in the proportions and metabolism of cellular lipids, abnormal functions of cellular membranes, altered activity of membrane-bound enzymes such as the SR Ca2+-ATPase, disturbances in cellular protein turnover and energy production and a variety of other changes all indicate that these inherited muscular dystrophies appear more like the results of oxidative stress to muscle than any other type of underlying muscle disturbance. Particular details of these altered characteristics of dystrophic muscle, in combination with current knowledge on the processes of oxidative damage to cells, may provide some insight into the underlying biochemical defect responsible for the disease, as well as direct research towards the ultimate goal of an effective treatment.

Ca-dependent slow action potentials in human skeletal muscle

Slow Ca-action potentials (CaAP) were studied in normal human skeletal muscle fibers obtained during surgery (fibers with both ends cut). Control studies also were carried out with intact as well as cut rat skeletal muscle fibers. Experiments were performed in hypertonic Cl-free saline with 10 or 84 mM Ca and K-channel blockers; muscles were preincubated in a saline containing Cs and tetraethylammonium. A current-clamp technique with two intracellular microelectrodes was used. In human muscle, 14.5% of the fibers showed fully developed CaAPs, 21% displayed nonregenerative Ca responses, and 64.5% showed only passive responses; CaAPs were never observed in 10 mM Ca. In rat muscle, nearly 90% of the fibers showed CaAPs, which were not affected by the cut-end condition. Human and rat muscle fibers had similar membrane potential and conductance in the resting state. In human muscle (22-32 degrees C, 84 mM Ca), the threshold and peak potential during a CaAP were +26 +/- 6 mV and +70 +/- 3 mV, respectively, and the duration measured at threshold level was 1.7 +/- 0.5 sec. In rat muscle, the duration was four times longer. During a CaAP, membrane conductance was assumed to be a leak conductance in parallel with a Ca and a K conductance. In human muscle (22-32 degrees C, 84 mM Ca, 40 micron fiber diameter), values were 0.4 +/- 0.1 microS, 1.1 +/- 0.7 microS, and 0.9 +/- 0.4 microS, respectively. Rat muscle (22-24 degrees C, 84 mM Ca) showed leak and K conductances similar to those found in human fibers. Ca-conductance in rat muscle was double the values obtained in human muscle fibers.

In vivo phosphorus nuclear magnetic resonance (31P-NMR) study of dystrophic hamster muscle

Skeletal muscle bioenergetics of dystrophic hamsters (DH) were studied by in vivo 31P-NMR in order to evaluate possible metabolic impairment. 31P-NMR data were obtained during rest, during muscle work that was induced by nerve stimulation at 3 frequencies (0.2, 0.4 and 1.0 Hz) and during postexercise recovery. At rest, phosphocreatine-to-inorganic phosphate ratio (PCr/Pi) was significantly (P less than 0.02) lower in adult DH (5.3 +/- 1.1; +/- 2 SD) compared with control hamsters (6.55 +/- 0.5). An increased PCr depletion was found in DH muscle during nerve stimulation and the steady-state PCr/Pi was significantly (P less than 0.05) lower at 0.4 and 1.0 Hz. Slow PCr/Pi recovery was observed in DH (0.5 +/- 0.2 units per min compared with 1.42 +/- 0.28 for control, +/- 2 SD, P less than 0.02). These findings suggest a significant in vivo mitochondrial malfunction in DH muscle that may result from either mitochondrial abnormalities or cardiac insufficiency or a combination of both.

Electron microscopic and autoradiographic characterization of hindlimb muscle regeneration in the mdx mouse

The pattern of postnatal growth and development of skeletal muscle in mdx mice was studied by light and transmission electron microscopy and by autoradiography and was compared with that in their normal age-matched controls at 4 and 32 weeks of age. The muscle weights of both the extensor digitorum longus (EDL) and soleus muscles of mdx mice were significantly greater than those in control mice at both ages. Body weights of male and female mdx mice were also increased over controls up to 12 weeks of age. At 4 weeks, both the EDL and soleus muscles exhibited focal areas of degeneration, necrosis, and regeneration of centrally nucleated extrafusal fibers resulting in a wide range of fiber sizes. By 32 weeks, the majority of fibers in both muscles were centrally nucleated, and focal areas of recent regeneration were observed. By electron microscopy, the course of macrophage infiltration into areas of degenerating fibers and the ongoing regeneration of myofibers within redundant cylinders of external lamina were noted. This pattern was frequent in 4-week-old mdx muscles and was present to a lesser degree at 32 weeks. A notable lack of both adipose tissue infiltration and fibrotic change in the endomysium were observed in muscles at both ages. Autoradiograms of muscles from 4-week-old mdx mice injected with tritiated thymidine showed an increased proportion of labeled sublaminal nuclei at 24 and 48 hours after injection compared to controls. At 32 weeks of age, labeling of nuclei in muscles of mdx mice was also greater than in controls, but was reduced compared to muscle labeling in 4-week-old mdx mice. The observed features of mdx muscle tissue suggest that this animal model is more applicable to the study of regeneration dynamics than to Duchenne-type human muscular dystrophy.

Beta-adrenergic ([3H] CGP-12177) receptors are elevated in slices of soleus muscle from CHE 147 dystrophic hamsters

We have utilized a muscle slice technique to compare the ontogeny of cell surface beta-adrenergic receptor binding in soleus and extensor digitorum longus (EDL) muscles of male Golden Syrian (GS) and Canadian Hybrid Farms 147 (CHF 147) dystrophic hamsters. Binding of the beta-adrenergic antagonist, [3H] CGP-12177 (CGP), to GS muscle slices was reversible, saturable, stereospecific and of high affinity. Bmax was higher in the soleus (2.57 +/- .12 fmol/mg wet wt) than in the EDL (1.6 +/- .17 fmol/mg wet wt) of adult animals while affinities were similar (0.35 +/- .06 and 0.24 +/- .04 nM respectively). No differences in binding characteristics were seen in EDL of GS compared to CHF 147 animals. In soleus slices frm GS hamsters, Bmax was highest at 16 days of age (5.72 +/- 0.26 fmol/mg), decreased between 16 and 29 days and remained constant until 300 days (2.51 +/- 0.52 fmol/mg). In dystrophic soleus slices, Bmax was also higher at 16 days than at any other age but receptor number decreased gradually, remaining higher than in GS until 90 days of age (p less than 0.05). The failure of beta-adrenergic receptor number to decrease at a normal rate may be implicated in the pathogenesis of hamster polymyopathy.

Progressive muscular dystrophy in a golden retriever dog: light microscope and ultrastructural features at 4 and 8 months

The clinical and morphological features of a congenital myopathy in a young male golden retriever dog were studied. Muscle biopsies at 4 and 8 months of age were examined with light and electron microscopy. Clinical features included early onset of generalized muscle weakness with selective muscle atrophy and hypertrophy, splaying of the limbs, stiff gait, and marked elevation of serum creatine kinase (CK). An electromyograph revealed spontaneous electrical activity characterized by sustained high-frequency activity, which was not abolished by neuromuscular blockade. Morphologically there was marked hypercontraction and segmental necrosis of muscle fibers with phagocytosis and regeneration. Ultrastructurally, dilatation of sarcoplasmic reticulum was the most consistent feature associated with early fiber degeneration. No abnormalities were noted in the central or peripheral nervous system. Progression of the disease was evident at 8 months. It was concluded that the findings are consistent with a dystrophic process of primary muscle origin. The probable genetics and comparison to other animal models of muscular dystrophy and to Duchenne dystrophy are discussed.

Elevation of calmodulin in avian muscular dystrophy

In an attempt to understand the mechanism of calcium accumulation in myopathies, changes in the major calcium-binding protein, calmodulin, was studied in genetically dystrophic chickens. Measurements by radioimmunoassay revealed an increase in the calmodulin concentration of dystrophic chicken muscles. Poly A-containing RNA(s) of fast and slow muscles from the normal and dystrophic chicks were hybridized with [32P]-labeled calmodulin cDNA probe by the dot-hybridization technique. Densitometric scan of the autoradiogram showed that the calmodulin mRNA levels of dystrophic fast muscles (pectoralis and posterior latissimus dorsi) were approximately two-fold higher than those of the corresponding normal muscles. No significant change in calmodulin and calmodulin messenger RNA of slow muscle (ALD) was found in dystrophic chickens. Our results suggest that increased calcium flux within the dystrophic muscle may be modulated by calmodulin.

Protein degradation in cultured skeletal muscle from Duchenne muscular dystrophy patients

The loss of contractile protein in Duchenne muscular dystrophy could result from low rates of synthesis, abnormally high rates of protein degradation, or a combination of both. We measured overall protein degradation rates in cultured human muscle cells obtained at biopsy from patients with Duchenne dystrophy or various muscle diseases and normal subjects. Measurements were performed on confluent cultures exhibiting no growth and containing a mixed cell population of myoblasts, fibroblasts, and multinucleated myotubes. Using a new double-isotope labeling protocol, we found protein degradation rates in all three groups to be similar (KD = 0.0171-0.0176 hr-1), suggesting no detectable abnormality of overall protein degradation in cells derived from Duchenne dystrophy patients.

Phospholipid composition of dystrophic chicken erythrocyte plasmalemmae. I. Isolation of a unique lipid in dystrophic erythrocyte membranes

Several structural and functional properties are characterized in nucleated erythrocyte plasmalemmae of age- and sex-matched dystrophic (line 413) and normal (line 412) chickens obtained from the University of California at Davis. Plasmalemma purity is assessed through marker enzymes. Significant differences are observed in the phospholipid content between dystrophic and normal chickens. The dystrophic chicken erythrocyte plasmalemma has an increased concentration of phosphatidylserine and a decreased concentration of phosphatidylethanolamine compared with control birds. Also, a measurable and distinct polar lipid, observed only on thin-layer chromatography (TLC) plates spotted with dystrophic preparations, is visualized adjacent to phosphatidylethanolamine. These abnormalities in the dystrophic chicken erythrocyte may signal a general defect in membrane structure for chicken dystrophy.

Myofibrillar M-line structure in normal and dystrophic hamster muscle

The presence of the specific myofibrillar M-line marker, myomesin , in isolated myofibrils and cryosections of skeletal and heart muscle as well as its appearance during differentiation in skeletal and heart muscle cell cultures of normal and dystrophic hamsters were evaluated. By means of the indirect immunofluorescence technique employing antibodies against chicken M-line proteins, the appearance of antigen localized in the M-line was investigated. No difference could be found between the M-line structure of normal and dystrophic animals. The results suggest that the M-line proteins, apparently relatively stable, are not primarily affected by the disease.

Post-ischemic calcification in skeletal muscle. A light microscopic study in the rat

The extent of post-ischemic calcification in skeletal muscle was studied in rats subjected to 5.5 h of ischemia followed by periods of reperfusion ranging from 30 min to 16 h. Sections from the tibialis posterior and soleus muscle were stained with alizarin red S (ARS) and were inspected with light microscopy. The number of ARS-positive cells increased during the first 5 h of reperfusion. The extent of calcification varied between fibers and the pattern of calcification appeared to be dependent on fiber type. In some fast glycogenolytic fibers (FG) central calcifications, probably representing mitochondria, were observed. In fast oxidative glycogenolytic (FOG) and slow oxidative (SO) fibers the most common pattern was an ARS-positive granulation, probably representing calcification of sarcoplasmic reticulum and/or mitochondria. The granulation was more extensive in FOG than in SO fibers. In some areas extracellular ARS-positive material was observed. In such areas, which probably represent areas of no-reflow, no calcification of muscle fibers was observed.

An elevated content of a unique lipid in dystrophic chicken embryonic myoblast membranes

A unique lipid, ethanolamine plasmalogen, is not only present abnormally in the plasmalemmae of erythrocytes from ex ovo dystrophic chickens but is also present abnormally in the membranes from embryonic myoblasts of in ovo dystrophic chickens.

Ca2+-dependent slow action potentials in normal and dystrophic mouse skeletal muscle

Slowly rising action potentials (APs), previously described in amphibian skeletal muscle, were examined in skeletal muscle of normal and dystrophic mice (129/ReJ strain). A standard two-microelectrode recording technique was used. Muscles were bathed in a solution that was Cl- free (methanesulfonate substituted), high in K+ (20 mM), and contained 15 mM tetraethylammonium. The slow APs were elicited under conditions in which the fast Na+ channels were voltage inactivated (by partial depolarization) and in which the external Na+ concentration was only 10 mM. Increases in external Ca2+ concentration produced increases in slow AP amplitude and duration. Mn2+ (4 mM), La3+ (4 mM), and detubulation with osmotic shock blocked the slow APs. When slow APs were generated at 30-s intervals, their amplitude stayed constant. When they were generated at 15-s intervals, their amplitude decreased progressively and then fell to zero by the 11th stimulus. The Ca antagonists verapamil (10(-5) M) and bepridil (10(-5) M) caused this decrease in amplitude to occur more quickly. Voltage inactivation of the slow APs occurred between -45 and -10 mV. Slow APs recorded from dystrophic muscle fibers were decreased in amplitude and duration compared with those in normal fibers, and there was a reduced incidence of occurrence; 96% of the fibers in normal muscle exhibited slow APs compared with only 46% of dystrophic muscle fibers. In summary, slow Ca2+ APs in mammalian muscle are similar to those in cardiac and amphibian skeletal muscle, and these slow APs are depressed in dystrophic skeletal muscle.

Intracellular elemental content of cardiac and skeletal muscle of normal and dystrophic hamsters

To test the hypothesis that the genetic lesion causing muscular dystrophy might be reflected in an abnormal intracellular elemental content, the elemental content of individual cardiac and skeletal muscle fibers in 50-day-old male control and cardiomyopathic BIO 53.58 hamsters was determined. The technique of electron probe x-ray microanalysis of freeze-dried tissue was employed. No electrolyte content differences were found between control and diseased animals for nuclei, myofibrillar cytoplasm, or mitochondrially-enriched cytoplasm of cardiac myocytes. Sulfur was elevated in dystrophic cardiac myocytes and was the only element significantly different in heart tissue of control and cardiomyopathic animals. Sulfur was also elevated in dystrophic soleus muscle fibers. The pattern of electrolyte content of these cells reflected a mixture of normal cells and damaged cells with altered electrolyte content. In this hamster model, alteration of electrolyte content of myocytes appears to be a result of the disease process and not an inherent characteristic of muscular dystrophy. The elevated sulfur in dystrophic hamster myocytes reflects a biochemical lesion which deserves further study.

Paradoxical effect of isoproterenol on hamster hereditary polymyopathy

Isoproterenol (ISO), a potent beta-adrenoreceptor agonist, was found to interfere with the development and progression of hamster hereditary polymyopathy. Cytoprotection involved both skeletal and heart muscles with reduced myofibrillar degeneration, phagocytosis, and an unusual scarring process rarely seen at this stage of the disease. A decrease in the Ca content of heart and hemidiaphragm homogenates corroborated these findings. The significant drop of serum creatine kinase with restoration of alkaline phosphatase activity towards normal values provided additional support to the therapeutic effect of ISO. Except for an increase in magnesium, there were no changes in serum electrolytes. The modifications in plasma membrane permeability together with improvement in microcirculation are some of the features whereby ISO can ameliorate muscle cell energy metabolism. It is inferred that the alleged primary role of calcium in the development of this inherited myopathy should be further scrutinized.

Mitochondrial calcium content and oxidative phosphorylation in heart and skeletal muscle of dystrophic mice

Mitochondrial calcium overloading was investigated in the genetically dystrophic mouse (strains 129/ReJ dy/dy) as a possible contributing factor to the development of muscle fiber necrosis. Mitochondrial calcium concentrations were significantly elevated in both skeletal muscle and heart organelles. Because mitochondria were isolated in the presence of ruthenium red this finding was not the result of an artefact of isolation. State 3 respiration rates and concomitantly the respiratory control ratios were slightly decreased in skeletal muscle, but not in heart mitochondria. This abnormality could result from calcium overloading in a small fraction of the mitochondria. Fractionation of skeletal muscle mitochondria on sucrose gradients gave two distinct populations of dystrophic organelles, one with high calcium, whereas normal skeletal muscle mitochondria and heart organelles showed only one broad band on the gradient. The results support the idea that both skeletal muscle and heart are affected in dystrophic mice, strain 129/ReJ dy/dy and also that in the dystrophic mouse the process of cell necrosis is associated with cellular calcium overloading.

The permissive role of catecholamines in the pathogenesis of hamster cardiomyopathy

It was previously shown that beta-adrenergic blockers exert a protective action on the development of heart necrotic changes in cardiomyopathic hamsters. To further investigate the possible role of catecholamines in the pathogenesis of the hamster hereditary cardiomyopathy, the ventricular adrenergic nerve terminals were visualized by fluorescence histochemistry, and NE uptake and turnover were determined after i.v. injection of labeled NE. It was found that the fluorescent nerve endings strongly proliferate with the occurrence of heart necrotic changes. With healing of the myocardial lesions, the difference between control and myopathic hearts is less apparent, and NE nerve endings are literally absent in the terminal stage of the disease. There was a marked increase in NE uptake during the necrotic stage and, at the same time, a considerable rise in elimination rate constant with a maximum level at terminal state, suggesting that the NE turnover is related to the progression of the disease. In light of the present findings, it can be surmised that NE plays a permissive role in the genesis of the hamster disease by promoting the heart necrotic changes.

Membrane alterations in skeletal muscle fibers of dystrophic mice

Skeletal muscle fibers from dystrophic mice and littermate controls (ReJ-129) were characterized electrically and then injected with an intracellular marker. In this way they could be identified for examination with an electron microscope to correlate the relative time course of electrical and ultrastructural alterations resulting from the dystrophic process. On the average, dystrophic muscle fibers displayed decreased membrane potentials (-59 +/- 1.2 vs -79 +/- 0.7 mV for normals), decreased specific membrane resistivity (517 +/- 27 vs 642 +/- 34 omega-cm2 for normals), and depressed action potential (AP) maximum rates of rise (+Vmax) (352 +/- 9 vs 417 +/- 9 V/s for normals) and amplitudes (92 +/- 1.2 vs 102 +/- 1.0 mV for normals) at an experimentally polarized membrane potential of -90 mV. Membrane resistivity and AP +Vmax were decreased even in those fibers from dystrophic muscles that displayed normal ultrastructure (classified visually and by ratio of sarcoplasmic reticulum to total cell volume). These findings support the membrane hypothesis of muscular dystrophy that membrane lesions are the primary lesion in the disease process.

Muscle glycolipids in inherited muscular dystrophy of chickens

Gangliosides and neutral glycolipids of muscles from normal and dystrophic chickens were studied. Total glycolipid content of the degenerating muscles was higher than the normal muscles. In addition, the myopathic muscles contained a ganglioside which was absent in the unaffected muscles from normal and dystrophic chickens. Based on the thin-layer chromatographic mobility, treatment with neuraminidases from Vibrio cholerae and Arthrobacter ureafaciens, and reactivity of the asialo-derivative towards anti-ganglio-N-triaosylceramide antibody, the dystrophic-specific ganglioside was tentatively identified as GM2. Data obtained from young and old dystrophic chickens suggested a direct relationship of this ganglioside to muscular dystrophy.

T system abnormalities in differentiating skeletal fibers of dystrophic chickens

Ultrastructural T system abnormalities are common in mature skeletal fibers from dystrophic chickens, but little is known of their development. Muscle strips from dystrophic and normal chickens aged 1 day through 4 weeks were examined in ultrathin plastic sections. At hatching, triads were sparse, with no apparent abnormalities. At 1 week, triads were more common; in some dystrophic fibers the T tubules were swollen, ballooned beyond the triad, or assembled asymmetrically, with or without supernumerary (greater than 2) junctional sarcoplasmic reticulum components. At 12 weeks, many dystrophic fibers also displayed degenerative changes, i.e., myofibrillar disintegration and cytoplasmic dispersion. At 4 weeks normal triad assembly was complete, T system abnormalities were widespread in dystrophic fibers. Fiber degeneration had progressed to breakdown and replacement. Thus, derangement of the T system (which parallels onset of muscle dysfunction) superimposed on triad assembly suggests that compromised excitation-contraction coupling is an early event in the chicken dystrophy.

Parenteral branched-chain amino acid treatment and avian dystrophy

Genetically homozygous line 413 dystrophic chickens were given twice-daily intraperitoneal injections of solutions containing branched-chain amino acids (BCCA-leucine, valine, isoleucine) either alone or in combination; and their alpha-ketoacid analogs (alpha-ketoisocaproic and alpha-ketoisovaleric acids). Another trial consisted of an amino acid mixture containing BCAA. Amino acid supplementation in each case significantly prolonged righting ability measured regularly by a standardized flip-test procedure. Enhanced functional ability was not generally accompanied by a decrease in plasma creatine kinase activity. However, a measurable increase in the affected pectoralis major muscle mass and protein content (female chickens in particular) was found with BCAA therapy. Moreover, the increase in muscle bulk was attended in some cases by a reduction in the relative number of degenerating fibers quantitated microscopically. Contrariwise, the amino acid mixture caused a reduction in pectoralis muscle mass. It is concluded that parenteral BCAA therapy offers limited benefit in retarding dystrophic symptoms in the chickens.

Fragmentation analysis of normal and dystrophic avian muscle

A difference between normal and dystrophic avian muscle was demonstrated by comparing the patterns of fragmentation of muscle during homogenization. Fragmentation was monitored by morphological methods and by viscometry. This method of fragmentation analysis depends on the principle that the viscosity of a suspension is an exponential function of the partial volume fraction occupied by the suspended particles; the more a tissue is fragmented into smaller pieces, the greater the viscosity of the resulting homogenate. Increasing the duration of homogenization of either fresh muscle in buffer or glycerinated muscle in relaxing solution gradually increased the viscosity of the homogenate of normal muscle, whereas the viscosity of the homogenate of dystrophic muscle remained approximately constant. This difference in viscosity indicated that dystrophic muscle was sheared into larger pieces which were resistant to further fragmentation. Electron microscopic examination showed that the homogenate of dystrophic muscle contained rows of sarcomeres, whereas normal muscle was sheared into amorphous masses of myofilaments.

Membrane myopathy: morphological similarities to Duchenne muscular dystrophy

Focal lesions in the plasma membrane overlying wedge-shaped defects in muscle fibers ("delta lesions") are an early pathological change in Duchenne muscular dystrophy (DMD). Abnormalities in the plasma membrane have been suggested as a cause of these lesions and of the degeneration of muscle fibers in DMD. We investigated the role of plasma membrane defects in the production of delta lesions by examining the effects of a series of membrane-active agents--lysolecithin, deoxycholate, Triton X-100, and melittin--on the muscles of rats in vivo. Within minutes after treatment with these agents, the muscle fibers developed typical delta lesions. Identical morphological changes were produced by the calcium ionophore A23187, suggesting that calcium entry may play an important role in this process. We conclude that damage to the plasma membrane or calcium entry can reproduce characteristic features of the muscle pathology seen in DMD. This model should prove useful in elucidating the mechanisms of muscle fiber damage and degeneration in DMD.

Hereditary polymyopathy and cardiomyopathy in the Syrian hamster. I. Progression of heart and skeletal muscle lesions in the UM-X7.1 line

The Syrian hamster polymyopathy is a hereditary disease, transmitted by an autosomal recessive gene, involving the heart and the entire musculature. The chronology of the pathologic events in the myocardium and skeletal muscle has been investigated in UM-X7.1 myopathic hamsters aged 0-250 days. A phasic pattern in the progression of the disease process was evident. Microscopic necrotic changes in the heart were visible prior to or at 50 days of age with increasing severity until 100 days of age and subsidence thereafter. More than 50% of the animals died before 250 days of age with signs of cardiac failure. The intensity and extent of myocardial calcific changes together with scar formation were determinant factors in curtailing the survival of animals. Changes in serum creatine kinase (CK) activity followed a phasic pattern similar to the progression of the myopathic disease. Because of the disparity of disease manifestations between the different myopathic hamster lines, it is essential to consider the time course of the heart and skeletal muscle microscopic changes when evaluating the severity of the hamster polymyopathy.

Evaluation of muscle degeneration in inherited muscular dystrophy by nuclear magnetic resonance techniques

Nuclear magnetic resonance (NMR) techniques were applied to study the muscular dystrophy in chicks. The water proton spin-lattice relaxation times (T1) of fast, slow, and mixed muscles and plasma were measured. The T1 values of dystrophic pectoralis major and posterior latissimus dorsi (PLD) were significantly higher than those of the normal pectoralis and PLD muscles. The present results establish a direct relationship between the differences in T1 values and the severity of muscle degeneration. Consistent with this conclusion, it was also found that the T1 values of muscles unaffected in muscular dystrophy, namely, the gastrocnemius, and anterior latissimus dorsi (ALD), were not different between the normal and dystrophic chicks. Although the affected muscles of dystrophic chicks contained higher percent water and fat than those of normal chicks, the results show that the higher T1 values in dystrophic muscles were not solely due to variations in their water content. The increase in the T1 values is principally a result of altered interaction between cellular water and macromolecules in the diseased muscles. These data also point out the potential use of NMR imaging in evaluating muscle degeneration.

Hereditary polymyopathy and cardiomyopathy in the Syrian hamster. II. Development of heart necrotic changes in relation to defective mitochondrial function

The mitochondrial oxidative phosphorylation, calcium and magnesium contents, and swelling-contraction activity were investigated in relation to the progression of the hereditary hamster cardiomyopathy. The assessment was made in animals between 22 and 232 days of age, which were divided into 7 groups according to stage of disease. In 24-day-old hamsters prior to development of heart necrotic changes, the membrane permeability of isolated mitochondria was altered. In 50-day-old animals, at a stage of disease when myocardial cells undergo degeneration, a defect of oxidative phosphorylation resulting from an increase in mitochondrial calcium was demonstrated. With culmination of the heart necrotic changes, at close to 100 days of age, mitochondrial dysfunction and calcium overload were maximal. There was a transient improvement during the healing stage, but the situation deteriorated with the occurrence of circulatory failure. Since the mitochondrial respiratory pattern and calcium overload parallel the cardiac degeneration, it is inferred that the cell energy depletion is a functional consequence of an abnormal calcium influx.

Therapeutic trial with protease inhibitor (leupeptin) in chicken muscular dystrophy. A histologic and histochemical study

For the purpose of observing the therapeutic benefit of protease inhibitors for progressive muscular dystrophy, a large quantity of doses of leupeptin of 10 mg/kg/day and 50 mg/kg/day were administered i.p. to male chickens afflicted with hereditary muscular dystrophy (line 413) for 4 months starting on the 7th day ex ovo. No clinical improvement was identified in physical ability as a result of the examination by flip test, and creatine kinase (CK) values. The number of necrotic fibers in the pectoralis superficialis (PS) muscle which is known to be preferentially damaged in dystrophic chicken, did not decrease significantly in the birds treated with 10 mg leupeptin/kg/day (number of necrotic fibers; 47.7/mm2) and 50 mg/kg/day (46.4/mm2) as compared to that of the untreated ones (43.2/mm2). A morphometric analysis of fiber diameter distribution also showed no statistical difference between the treated and untreated birds. In the second group, 10 mg leupeptin/kg and a combination of leupeptin and bestatin of 10 mg/kg each were injected directly into the left lower half of the PS muscle three times a week for 4 months. Necrotic fibers were still present in the injected site, remote area of the left upper PS muscle treated with leupeptin (52.7/mm2), leupeptin and bestatin (52.2/mm2), and contralateral right upper PS muscle (41.6 and 53.5/mm2, respectively). The number of necrotic fibers in treated muscles was again not significantly different from that in untreated dystrophic ones (39.6/mm2). In fiber diameter analysis, no statistical difference was recognized between the treated and untreated dystrophic muscles.

Nuclear magnetic resonance study of muscle water protons in muscular dystrophy of chickens

Using the pulsed nuclear magnetic resonance (NMR) spectroscopy, the spin-lattice (T1) and the spin-spin (T2) relaxations times of water protons from samples of pectoralis major muscles of normal (line 412) and homozygous dystrophic (line 413) chickens were measured. Both the T1 and T2 were significantly increased (P less than 0.05) in the dystrophic muscles. The mean values of the relaxation times are given +/- S.D. The T1 values were 654 +/- 22 msec in normal and 692 +/- 41 msec in dystrophic muscles. The T2 values for normal and dystrophic muscles were 39 +/- 4 msec and 52 +/- 7 msec, respectively. Although the water content of dystrophic muscles (78.9 +/- 0.6%) determined by gravimetric methods was significantly higher than normal muscles (74.9 +/- 1.1%), this difference in tissue hydration could not explain quantitatively the increase of T1 and T2 values in the dystrophic muscles. The results of the measurements of the relaxation times seem to suggest that there are changes in the composition and/or conformational state of the proteins.

Intracytoplasmic vacuoles in alpha W fibers of dystrophic chicken muscle--probable early pathologic event initiates massive fiber necrosis

An electron-microscopic study on dystrophic chicken white muscle, posterior latissimus dorsi (PLD), was performed with histochemical identification of three fiber types of beta R (red), alpha R and alpha W (white) fibers to evaluate the pathophysiology in fiber necrosis. As seen in histochemically stained sections, vacuolar formation in the cytoplasm, an outstanding pathologic feature in chicken dystrophy, was recognized in the alpha W fibers by electron microscopy. The vacuole was membrane-bound and thought to originate from coalescence or dilatation of extensively proliferated sarcotubular system. There was evidence of a delay in fiber type transformation from alpha R to alpha W in dystrophic white muscle, while the initial pathologic event of sarcotubular system proliferation might be expressed only after muscle fibers had attained histochemical characteristics of alpha W fibers. Localized myofibrillar degeneration was encountered in the vicinity of the vacuole with focal membrane defect. An influx of extracellular fluid through the vacuolated sarcotubular system into the sarcoplasm may activate certain proteases, such as calcium-dependent protease because the extracellular fluid contains high concentration of calcium ion. The activated protease then degrades structural protein, especially Z-line protein, followed by fiber necrosis with phagocytosis.