Diaphragm Of Mice Research Articles

Developmental induction of DHPR alpha 1s and RYR1 gene expression does not require neural or mechanical signals.

This study compares dihydropyridine receptor (DHPR) and ryanodine receptor (RyR1) gene expression in the diaphragm and hindlimb skeletal muscles of neonatal mice, and examines the contribution of neural and mechanical signals to their developmental induction in vivo. DHPR alpha 1s subunit and RyR1 protein are expressed concurrently, while their respective mRNAs are induced sequentially, with DHPR mRNA ahead of RyR1 mRNA. Both DHPR and RyR1 are more abundant in the diaphragm at birth, and become more abundant in the hindlimb at maturity. These patterns are consistent across different muscles and species. A critical period for DHPR alpha 1s and RyR1 gene expression in the hindlimb occurs between days 5 and 19 postnatal. Their mRNA expression during this period is unchanged by denervation or tenotomy, but DHPR protein decreases after tenotomy. These results demonstrate that both transcriptional and post-transcriptional mechanisms contribute to the muscle-specific and coordinated assembly of the functional DHPR-RyR1 complex, and that the developmental induction of DHPR and RyR1 gene transcription does not require neural or mechanical signals.

Molecular structure-function relationship in the slit diaphragm

The past 5 years have witnessed an exponential increase in our understanding of the structure and function of the glomerular slit diaphragm. The identification of nephrin as the first transmembrane slit diaphragm protein was a watershed event in slit diaphragm biology. This article correlates some of the observations of the prenephrin era with more recent studies, and elaborates on the individual characteristics of each slit diaphragm protein. Recent studies on protein-protein interactions related to slit diaphragm permeability and cell signaling are elaborated, along with observations on their expression in human disease and experimental models of proteinuria. Developmental expression of components of the slit diaphragm in normal and knockout mice also is discussed. Finally, some areas of future investigation are proposed.

Development of the peritoneal lymphatic stomata and lymphatic vessels of the diaphragm in mice

The generation and development of the peritoneal lymphatic stomata (PLS) and lymphatic vessels of the diaphragm were studied in mice at gestational ages from the embryonic to the postnatal period with TEM, SEM and enzyme histochemistry and the PLS data were quantitatively analyzed with computer-assisted image processing technology (Elescope image analysis software). The results showed that the diaphragmatic mesothelium was covered only by flattened mesothelial cells (FMC) at the 13th embryonic day (ED 13). At ED 15, some cuboidal mesothelial cells (CMC) and immature lymphatic stomata (NLS) were found scattered on the diaphragmatic mesothelium. The sub-peritoneal lymphatic capillaries did not appear until ED 18. However, no absorptive function was observed in NLS when trypan blue granules were injected into the peritoneal cavity. At postnatal day 1 (PND 1), the endothelial cytoplasm processes of the diaphragm lymphatic capillaries span the connective tissue fibers and the basal membrane of CMC to form the subperitoneal channels. These channels were connected with NLS and serve as the absorptive route between the peritoneal cavity and the sub-peritoneal lymphatic vessels. The trypan blue absorption test demonstrated that postnatal PLS possessed an absorptive function and had transformed to mature lymphatic stomata (MLS) by PND 1. Thus, NLS were renamed of MLS. At PND 5, the cuboidal mesothelial cell ridge (CMCR) appeared with increased CMC areas. At PND 10, CMCR were fused to form the band-like CMC area with much more MLS distributed in the muscular portion of the diaphragm. With distribution area and density of PLS increasing and growth of lymphatic vessels, an increased absorptive function from the peritoneal cavity was observed in the experiment.

Altered muscle force and stiffness of skeletal muscles in alpha-sarcoglycan-deficient mice.

Alpha-sarcoglycan (ASG) is a transmembrane protein of the dystrophin-associated complex, and absence of ASG causes limb-girdle muscular dystrophy. We hypothesize that disruption of the sarcoglycan complex may alter muscle extensibility and disrupt the coupling between passive transverse and axial contractile elements in the diaphragm. We determined the length-tension relationships of the diaphragm of young ASG-deficient mice and their controls during uniaxial and biaxial loading. We also determined the isometric contractile properties of the diaphragm muscles from mutant and normal mice in the absence and presence of passive transverse stress. We found that the diaphragm muscles of the null mutants for the protein ASG show 1) significant decrease in muscle extensibility in the directions of the muscle fibers and transverse to fibers, 2) significant reductions in force-generating capacity, and 3) significant reductions in coupling between longitudinal and transverse properties. Thus these findings suggest that the sarcoglycan complex serves a mechanical function in the diaphragm by contributing to muscle passive stiffness and to the modulation of the contractile properties of the muscle.

Ca2+ Release Induced by Cyclic ADP Ribose in Mice Lacking Type 3 Ryanodine Receptor

The action of cyclic-ADP-ribose was studied on calcium release from sarcoplasmic reticulum of skeletal muscles of neonatal and adult wild-type and RyR3-deficient mice. cADPR increased calcium efflux from microsomes, enhanced caffeine-induced calcium release, and, in 20% of the tests, triggered calcium release in single muscle fibers. These responses occurred only in the diaphragm of adult RyR3-deficient mice. cADPR action was abolished by ryanodine, ruthenium red, and 8-brome-cADPR. These results strongly favor a specific action of cADPR on RyR1. The responsiveness of RyR1 appears in adult muscles when RyR3 is lacking.

Most apoptotic cells in mdx diaphragm muscle contain accumulated lipofuscin.

An age-related pigment, lipofuscin (LF), which accumulates in postmitotic, long-lived cells, is formed by the oxidative degradation of cellular macromolecules by oxygen-derived free radicals. In the present study we show that LF is accumulated in some myofibres, myosatellite cells and interstitial cells in the diaphragm muscles of the X chromosome-linked muscular dystrophic (mdx) mice at the age of 10 weeks when repetitive cycles of de- and regeneration of myofibres occur. In contrast, LF is virtually absent in diaphragm muscles of age-matched C57BL/10 (C57) normal control mice. Therefore, mdx muscle is more susceptible to oxidative stress than normal muscle. We hypothesise that gene-regulated cell death (apoptosis) occurs in dystrophic muscle cells that accumulate LF as a consequence of either oxidative stress or injury. We found that 74-79% of apoptotic myosatellite cells, interstitial cells and myofibres in mdx diaphragm contain accumulated or dotted LF granules, but only 12-20% of non-apoptotic cells contain LF. Apoptotic cells are very rare in the diaphragm of age-matched C57 control mice. This suggests that the regeneration of mdx diaphragm muscle initiated from myosatellite cells is impaired by their apoptosis as the result of either oxidative stress or a product of oxidative injury.

Spontaneous Activity of Murine Neuromuscular Junctions in the Presence of Dantrolene

By recording miniature end-plate potentials (mEPP), the effects of dantrolene (10-100 μM), a blocker of ryanodine receptors, were studied on the isolated diaphragm of mice. The effects to be studied were as follows: on spontaneous secretion of acetylcholine quanta and on the pattern of interaction with ryanodine effects. Two-hour-long application of dantrolene to the muscle caused no significant changes in the amplitude and dispersion (σ2) of mEPP, nor on its time course. In the presence of 100 μM dantrolene, the mean frequency of mEPP increased, on average, by 58.3 ± 5.9% (P < 0.05). Dantrolene suppressed in a dose-dependent manner a number of ryanodine effects (this agent was used in a concentration of 0.5 μM as an intensifier of intracellular Ca2+ mobilization): it completely prevented the appearance of the population of high-amplitude (the so-called giant) mEPP, reduced by 50-80% the increment of the mEPP amplitude dispersion, and increased by 25-45% the mEPP mean amplitude; the above effects were induced by ryanodine application for 120 min. After preliminary application of dantrolene (10-100 μM), ryanodine caused an effect not observable in the absence of dantrolene: mEPP became more frequent (140-210%). Thus, when acting on motor synapses, dantrolene behaves as a nontoxic agent, inducing only a presynaptic effect – a moderate increase in the mEPP frequency. The dual character of interaction between dantrolene and ryanodine in motor synapses was observed: on the one hand, dantrolene acts as a physiological antagonist of ryanodine by reducing the ryanodine-induced increase of dispersion and mEPP amplitude; on the other hand, dantrolene unmasks the ability of ryanodine to increase the mEPP frequency.

Cardiac-specific overexpression of tumor necrosis factor-alpha causes oxidative stress and contractile dysfunction in mouse diaphragm.

We have developed a transgenic mouse with cardiac-restricted overexpression of tumor necrosis factor-alpha (TNF-alpha). These mice develop a heart failure phenotype characterized by left ventricular dysfunction and remodeling, pulmonary edema, and elevated levels of TNF-alpha in the peripheral circulation from cardiac spillover. Given that TNF-alpha causes atrophy and loss of function in respiratory muscle, we asked whether transgenic mice developed diaphragm dysfunction and whether contractile losses were caused by oxidative stress or tissue remodeling. muscles excised from transgenic mice and littermate controls were studied in vitro with direct electrical stimulation. Cytosolic oxidant levels were measured with 2', 7'-dichlorofluorescin diacetate; emissions of the oxidized product were detected by fluorescence microscopy. Force generation by the diaphragm of transgenic animals was 47% less than control (13.2+/-0. 8 [+/-SEM] versus 25.1+/-0.6 N/cm(2); P:<0.001); this weakness was associated with greater intracellular oxidant levels (P:<0.025) and was partially reversed by 30-minute incubation with the antioxidant N:-acetylcysteine 10 mmol/L (P:<0.01). Exogenous TNF-alpha 500 micromol/L increased oxidant production in diaphragm of wild-type mice and caused weakness that was inhibited by N:-acetylcysteine, suggesting that changes observed in the diaphragm of transgenic animals were mediated by TNF-alpha. There were no differences in body or diaphragm weights between transgenic and control animals, nor was there evidence of muscle injury or apoptosis. Elevated circulating levels of TNF-alpha provoke contractile dysfunction in the diaphragm through an endocrine mechanism thought to be mediated by oxidative stress.

Morphological effects of an anabolic steroid on muscle fibres of the diaphragm in mice.

Until recently, rats have been used for studies on the effects of anabolic steroids (AS) for improving physical performance. However, no consistent results on the changes in muscle fibre volume have ever been obtained. In this study we investigated the morphological effects of nandrolone phenylpropionate, an AS, on the muscle fibres of the diaphragm in adult male mice. AS (5 mg kg(-1) week(-1)) was injected intramuscularly in the experimental group (AS-administration group), and peanut oil (0.08 ml week(-1)) was injected in the control group. The cross-sectional areas of Type I (red) and Type II (white and intermediate) muscle fibres after 4 weeks of AS administration were 135% and 139% larger than those in the control group, respectively. The mean cross-sectional areas of mitochondria in the subsarcolemmal (SS) region and interfibrillar (IF) region in Type I fibres and the SS region of the Type II muscle fibres in the AS-administration group were 139%, 135% and 124% larger than those in the control group, respectively. No significant differences in the cross-sectional area of mitochondria were noted between the group of mice administered with AS for 8 weeks and the control group, showing that the effect of the AS administration attained a peak at 4 weeks, but that the effect of the 8 weeks of AS administration declined. We concluded from these results that the response of Type I muscle fibres to AS is stronger than that of Type II muscle fibres, as is the response of SS mitochondria compared to IF mitochondria. We also suggested that the two types of mitochondria may have different roles and that administration of AS may cause a different response in the two types of mitochondria.

Vitamin B6-deficient diet plus 4-deoxypyridoxine (4-DPD) reduces the inflammatory response induced by T. spiralis in diaphragm, masseter and heart muscle tissue of mice.

Animals fed diets deficient in vitamin B6 develop microcytic anemia, alterations of growth, and other pathologies. 4-deoxypirydoxine is a potent antagonist of vitamin B6 coenzyme which depresses IL-1, TNF and IL-6 and has anti-inflammatory properties. The aim of this study was to show the anti-inflammatory effects of 4-DPD on chronic inflammation caused by the nematode parasite T. spiralis, specifically on the recruitment and the activation of inflammatory cells. Two groups of mice, 6 weeks of age, were used: one was maintained on a vitamin B6-deficient synthetic pellet diet for 15 days before injection of the nematode, and administered an intraperitoneal injection (i.p.) of 4-DPD (250 microg/mouse) for 15 days (the first, 5 days before infection), and the second group was maintained on a normal diet for the total duration of the experiment. These two groups were then injected with 150 larvae (L1-T7 spiralis) per os. Chronic inflammation was caused by infection of treated or untreated mice with T7 spiralis parasite. After 14 days post-infection all mice developed a chronic inflammatory response. Mice fed with a B6-deficient diet showed a significant decrease in the number of cysts found in the diaphragm when compared to mice treated with normal diet. In addition, in all mice treated with vitamin B6-deficient diet plus 4-DPD the average body weight was significantly lower, compared to the mice on normal diet in all weeks examined. Moreover, in sections of the diaphragm, masseter and myocardium muscles, the infiltration of inflammatory cells, such as macrophages, lymphocytes, and eosinophils were more intense in untreated mice compared to those fed a vitamin B6-deficient diet. These results show that BALB/c mice infected with T. spiralis and fed a vitamin B6-deficient diet plus the vitamin B6 antagonist, 4-DPD, prolong the time of invasion of the larvae in the muscle cells, influence the recruitment of inflammatory cells and the intensity of the inflammatory reaction compared to infected untreated mice (control).

Metastatic sublines of an SV40 large T antigen immortalized human prostate epithelial cell line.

The available human prostate cancer cell lines that are metastatic in athymic nude mice all have complex, highly aneuploid karyotypes. Other prostatic cells immortalized by transforming genes of SV40 or HPV and converted to tumorigenicity by additional genetic manipulation are not reported to be metastatic. Tumorigenic sublines of human prostate epithelial cells previously immortalized by transfection with the SV40T antigen gene were obtained by sequential passage in male athymic nude mice. These sublines were evaluated histopathologically for tumorigenicity and metastasis in athymic nude mice after subcutaneous, intraperitoneal, and intraprostatic injection. Each subline was characterized by standard (GTG-banding) cytogenetic and FISH analysis, and RNase protection assays for androgen receptor expression. Two sublines produced metastases in lungs and the diaphragm of most mice after either intraprostatic or intraperitoneal injection. The M2205 subline formed large local tumors after intraprostatic injection. Cytogenetic aberrations present in the metastatic sublines, but not in the tumorigenic, nonmetastatic lines or the parental P69SV40T line, included dup(11)(q14q22), der(16) t (16;19) (q24;q13.1), which resulted in the loss of the short arm and proximal long arm of chromosome 19 (19q13.1-->19pter), and loss of the Y chromosome. None of the sublines expressed the androgen receptor. These cytogenetically defined, SV40T-immortalized human prostate epithelial cell lines, with distinct biological behaviors in vivo, provide additional tools for the genetic analysis of the emergence of metastatic capacity.

Respiratory muscles as a target for adenovirus-mediated gene therapy.

The protein dystrophin is absent in the muscles of patients with Duchenne muscular dystrophy (DMD) as well as dystrophin-deficient mice with muscular dystrophy (mdx mice). The mdx mouse diaphragm closely resembles the human DMD phenotype and thus provides a useful model for studies of dystrophin gene replacement. Recombinant adenovirus vectors (AdVs) hold promise as a means for delivering a functional dystrophin gene to muscle. As an initial step toward this goal, we have determined the efficiency and functional consequences of AdV-mediated reporter gene transfer to the diaphragm in both normal and mdx adult mice. At 1 week after AdV administration, there was a high level of transgene expression in the diaphragm. One month later, however, elimination of transgene expression was observed along with a significant decrease in force production by both normal and mdx diaphragms. Immunosuppression with cyclosporine did not augment the level of transgene expression, but a beneficial effect on diaphragm force-generating capacity was observed in both groups of animals. In order to further elucidate the cellular mechanisms underlying these findings, the effects of AdV gene inactivation (by ultraviolet (UV) irradiation) and interference with host T-lymphocyte subsets were examined. Both UV-inactivation of AdV and CD8+ T-cell deficiency were found to significantly alleviate AdV-induced reductions in diaphragm force-generating capacity. Brief (2 day) administration of a neutralizing antibody against host CD4+ T-cells also produced a trend towards mitigation of AdV-induced contractile dysfunction. In addition, transgene expression one month after AdV delivery was significantly enhanced with inhibition of either CD4+ or CD8+ T-cell function. The data suggest two major sources of reduced force generation after recombinant adenovirus vector-mediated gene transfer to muscle: 1) a cytotoxic component associated with recombinant adenovirus vector transcriptional activity; and 2) an immune-based component of more delayed onset that is primarily dependent upon CD8+ T-cell activity. These results have important implications for the design of future generation vectors and the potential need for immunosuppressive therapy after recombinant adenovirus vector mediated dystrophin gene transfer to Duchenne muscular dystrophy patients.

Involvement of nitric oxide in the in vivo effects of lipopolysaccharide on the contractile and electrical properties of mouse diaphragm.

The contractile and electrical properties of the mouse diaphragm during endotoxemia were studied, and the possible role of nitric oxide (NO) on these changes was investigated. The mice were injected intraperitoneally with E. coli. lipopolysaccharide (endotoxin, LPS) at various times before isolation of the diaphragm to induce endotoxemia. It was observed that direct twitch tension was slightly increased, and that there was a significant increase in tetanic tension when compared with controls. The potentiation of direct twitch tension induced by a Cl--channel blocker (9-anthracene carboxylic acid), but not the potentiation by a Na+-channel activator (veratridine) or by K+-channel blockers (uranyl ion, 4-aminopyridine and tetraethylammonium ion), was attenuated in the diaphragm of LPS-treated mice. Moreover, the resting membrane potential was significantly reduced and the membrane input resistance was significantly increased, largely due to a decrease in Cl--conductance. However, the membrane K+-conductance remained unaltered. These results imply that the sarcolemmal Cl--channel is markedly affected in the mouse diaphragm during endotoxemia. These changes of contractile and electrical characteristics of the mouse diaphragm during endotoxemia could be reversed by treatment with dexamethasone and N(G)-nitro-L-arginine (NO synthase inhibitors). On the other hand, in in vitro studies, LPS (20 microg/ml), by itself, applied directly to the diaphragm, did not alter the muscle contractions or the membrane potentials. A NO donor, added to the diaphragm bath, increased the tetanus/twitch ratio and induced a transient depolarization. All of these findings suggest that LPS may, at least in part, affect the sarcolemmal electrical properties and muscle contractions during endotoxemia through the L-arginine:NO pathway.

The in vivo effect of lipopolysaccharide on neuromuscular transmission in the mouse

The in vivo effect of lipopolysaccharide (endotoxin) on nerve-evoked muscle contractions and neuromuscular transmission was studied in the mouse phrenic nerve-diaphragm preparations. In lipopolysaccharide-treated mouse diaphragms it was observed that indirectly induced twitch tension was unchanged while tetanic tension significantly decreased. Neostigmine (50 nM) increased the amplitude of nerve evoked muscle contractions, while it caused partial fade of tetanic contractions (Wedensky inhibition) and accelerated the run-down of end-plate potentials (e.p.ps.) evoked by repetitive nerve stimulation, in the diaphragm of saline-control mice, but not of lipopolysaccharide-treated mice. These effects of neostigmine could be abolished by ouabain (5 μM). Measurement of the quantal contents of e.p.ps. revealed that ouabain (5 μM) significantly increased it in the diaphragm of saline-control mice to an extent similar to that in diaphragm of lipopolysaccharide-treated mice. Moreover, ouabain-sensitive Na +, K +-ATPase activity in the sciatic nerve of lipopolysaccharide-treated mice was markedly decreased. The alterations in neuromuscular transmission of the diaphragm during endotoxemia could be reversed by the administration of polymyxin B (a lipopolysaccharide neutralizer) and N G-nitro- l-arginine (a nitric oxide (NO) synthase inhibitor), suggesting that NO is involved in these lipopolysaccharide-induced alterations of neuromuscular transmission mediated by an impairment of ouabain-sensitive Na +, K +-ATPase activity in mouse motor nerves.

Electrical properties of diaphragm and EDL muscles during the life of dystrophic mice.

The membrane electrical properties of diaphragm and extensor digitorum longus (EDL) muscle fibers of dystrophic mdx and control mice from 4 wk to 14-19 mo of age were recorded with the intracellular microelectrode technique. Up to 8 wk of age, the diaphragm and EDL muscles did not differ between the two strains. From 8 up to 20 wk, the mdx diaphragm fibers showed a higher membrane resistance (Rm), which was due to significantly lower values of resting chloride conductance (GCl) and an overexcitability with respect to age-matched controls. Oppositely, the mdx EDL muscle fibers had significantly lower Rm and higher GCl values than age-related controls at 8, 10, and 13 wk, along with a decreased membrane excitability. These differences were no longer detectable at 20 wk. The diaphragm and EDL muscles from 14- to 19-mo-old controls showed a decrease of GCl and an increase of potassium conductance with respect to adult animals. In aged mdx animals, these changes were very dramatic in diaphragm fibers, whereas no differences, with respect to adults, were found in the EDL muscle. Thus GCl is an index of the dystrophic condition of mdx muscles. In the degenerating diaphragm, the impairment of GCl can account for some of the pathological features of the muscle. In the EDL muscle, the changes of GCl can follow the high regenerative potential of the hindlimb muscles of the mdx phenotype.

Expression of the inducible nitric oxide synthase gene in diaphragm and skeletal muscle.

Nitric oxide (NO) is a pluripotent molecule that can be secreted by skeletal muscle through the activity of the neuronal constitutive isoform of NO synthase. To determine whether skeletal muscle and diaphragm might also express the macrophage-inducible form of NO synthase (iNOS) during provocative states, we examined tissue from mice at serial times after intravenous administration of Escherichia coli endotoxin. In these studies, iNOS mRNA was strongly expressed in the diaphragm and skeletal muscle of mice 4 h after intravenous endotoxin and was significantly diminished by 8 h after challenge. Induction of iNOS mRNA was followed by expression of iNOS immunoreactive protein on Western immunoblots. Increased iNOS activity was demonstrated by conversion of arginine to citrulline. Immunochemical analysis of diaphragmatic explants exposed to endotoxin in vitro revealed specific iNOS staining in myocytes, in addition to macrophages and endothelium. These results may be important in understanding the pathogenesis of respiratory pump failure during septic shock, as well as skeletal muscle injury during inflammation or metabolic stress.

Elevated levels of albumin in soleus and diaphragm muscles of mdx mice.

Muscle damage is often associated with an influx of extracellular fluid containing albumin into the muscle. Muscles affected by muscular dystrophy undergo severe muscle damage; therefore, the hypothesis was tested that muscles of dystrophic (mdx) mice contain elevated levels of albumin. Albumin levels in diaphragm (DIA) and soleus (SOL) muscles of control and mdx mice were measured at 3 months and 1 year of age. Albumin in mdx DIA at 1 year of age was twice that of control. In mdx SOL at 1 year of age albumin was increased 25% compared with control. The increase in albumin correlates well with the decline in function in mdx DIA and SOL muscles. Electron microscopy of muscles suggests that albumin is co-localized with transverse tubules of muscle fibers and thus may be mainly located in extracellular fluid. We conclude that albumin is elevated in muscles affected by muscular dystrophy and suggest that this may be of clinical importance in view of substances bound to albumin under physiological conditions.

Effects of aging and/or training on antioxidant enzyme system in diaphragm of mice

We investigated the effects of aging and/or swimming training on the antioxidant enzyme system in diaphragm of mice. Young (2 months old) and old (26 months old) male mice were swimming-trained for 6 weeks (1 h/day, 5 days/week). Cu,Zn-Superoxide dismutase (Cu,Zn-SOD) activity was significantly upregulated with aging, and swimming training definitely enhanced the activity only in young mice. Neither aging nor swimming training had overt effect on Mn-SOD activity. Glutathione peroxidase activity in young mice was significantly increased after training, but not in old mice. Both of immunoreactive Cu,Zn-SOD and Mn-SOD were significantly increased with aging but were unaffected by swimming training. Consequently, physical training significantly enhanced the specific activity of Cu,Zn-SOD in young mice, but not in old mice. Meanwhile, swimming training significantly increased xanthine oxidase activity in both age groups, the extent of the increase being greater in old mice than in young mice. We concluded that the antioxidant enzyme system in mouse diaphragm trends to be upregulated with aging, but that swimming training improved the system only in young mouse diaphragm.

Extraocular, limb and diaphragm muscle group-specific antioxidant enzyme activity patterns in control and mdx mice

The mechanisms primarily responsible for the degenerative processes occurring in dystrophic skeletal muscle remain unresolved. The identification of the mechanisms that lead to the complete sparing of extraocular muscle in dystrophinopathies is of particular interest. A number of studies have provided evidence to suggest that the muscle pathology that characterizes muscular dystrophy may be, in part, free radical mediated. In the present study, we examined the antioxidant enzyme status of extraocular, diaphragm and gastrocnemius muscles in control strain and mdx mice. Our results revealed that in the control strain, both extraocular and diaphragm muscles had higher copper/zinc superoxide dismutase, manganese superoxide dismutase and selenium dependent glutathione peroxidase activities as compared to the gastrocnemius. Furthermore, the diaphragm had higher glutathione reductase activity as compared to the gastrocnemius. These findings indicate that the highly aerobic extraocular and diaphragm muscles have higher antioxidant enzyme capacity than the gastrocnemius, a muscle more dependent on anaerobic energy metabolism. Changes in the antioxidant enzyme status of the mdx mouse correlated, in part, with the degree of histopathological involvement of the three muscle groups assessed.

Extraocular, limb and diaphragm muscle group-specific antioxidant enzyme activity patterns in control and mdx mice

The mechanisms primarily responsible for the degenerative processes occurring in dystrophic skeletal muscle remain unresolved. The identification of the mechanisms that lead to the complete sparing of extraocular muscle in dystrophinopathies is of particular interest. A number of studies have provided evidence to suggest that the muscle pathology that characterizes muscular dystrophy may be, in part, free radical mediated. In the present study, we examined the antioxidant enzyme status of extraocular, diaphragm and gastrocnemius muscles in control strain and mdx mice. Our results revealed that in the control strain, both extraocular and diaphragm muscles had higher copper/zinc superoxide dismutase, manganese superoxide dismutase and selenium dependent glutathione peroxidase activities as compared to the gastrocnemius. Furthermore, the diaphragm had higher glutathione reductase activity as compared to the gastrocnemius. These findings indicate that the highly aerobic extraocular and diaphragm muscles have higher antioxidant enzyme capacity than the gastrocnemius, a muscle more dependent on anaerobic energy metabolism. Changes in the antioxidant enzyme status of the mdx mouse correlated, in part, with the degree of histopathological involvement of the three muscle groups assessed.