Pre-clinical study of 21 approved drugs in the mdx mouse.

Duchenne muscular dystrophy, a genetic disease caused by the absence of functional dystrophin, remains without adequate treatment. Although great hopes are attached to gene and cell therapies, identification of active small molecules remains a valid option for new treatments. We have studied the effect of 20 approved pharmaceutical compounds on the muscles of dystrophin-deficient mdx5Cv mice.

Diaphragm tension reduced in dystrophic mice by an oxidant, hypochlorous acid.

In dystrophin-deficient skeletal muscle cells, in which Ca2+ homeostasis is disrupted and reactive oxygen species production is increased, we hypothesized that hypochlorous acid (HOCl), a strong H2O2-related free radical, damages contractile proteins and the sarcoplasmic reticulum. The aim of the present study was to investigate the effects of exposure to oxidative stress, generated by applying HOCl (100 micromol/L and 1 mmol/L), on the contractile function and sarcoplasmic reticulum properties of dystrophic mice. Experiments were performed on diaphragm muscle, which is severely affected in the mdx mouse, and the results were compared with those obtained in healthy (non-dystrophic) mice.

Increased Ca2+ storage capacity of the skeletal muscle sarcoplasmic reticulum of transgenic mice over-expressing membrane bound calcium binding protein junctate.

Junctate is an integral sarco(endo)plasmic reticulum protein expressed in many tissues including heart and skeletal muscle. Because of its localization and biochemical characteristics, junctate is deemed to participate in the regulation of the intracellular Ca2+ concentration. However, its physiological function in muscle cells has not been investigated yet.

Greater susceptibility of the sarcoplasmic reticulum to H2O2 injuries in diaphragm muscle from mdx mice.

The aim of the present study was to investigate the direct effects of a reactive oxygen species, H(2)O(2), on the contractile function and sarcoplasmic reticulum properties of dystrophin-deficient diaphragm using chemically skinned fibers and sarcoplasmic reticulum vesicle preparations. The results obtained using Triton X-100-skinned fibers demonstrate that exposure to 1 mM H(2)O(2) had similar effects on the maximal Ca(2+)-activated tension and on the Ca(2+) sensitivity of the contractile apparatus of diaphragm fibers in Bl10 and mdx mice. The effects of H(2)O(2) were also assessed on sarcoplasmic reticulum function using saponin-skinned fibers and sarcoplasmic reticulum vesicle preparations.

Adenosine affects the release of Ca2+ from the sarcoplasmic reticulum via A2A receptors in ferret skinned cardiac fibres.

In this study, it was shown that adenosine potentiates caffeine-induced Ca2+ release. It was then proposed that the enhancement of the caffeine-induced Ca2+ release might occur by a direct effect on the ryanodine Ca2+ release channel or on other Ca2+ regulation mechanisms. Furthermore, A2A receptors may be functional on the ferret cardiac sarcoplasmic reticulum.

Novel sarco(endo)plasmic reticulum proteins and calcium homeostasis in striated muscles.

The impact of calcium signaling on many cellular functions is reflected by the tight regulation of the intracellular Ca(2+) concentration that is ensured by diverse pumps, channels, transporters and Ca(2+) binding proteins. In this review, we present recently identified novel sarco(endo)plasmic reticulum proteins that may have a potential involvement in the regulation of Ca(2+) homeostasis in striated muscles.

Ryanodine receptor 1 mutations, dysregulation of calcium homeostasis and neuromuscular disorders.

The skeletal muscle ryanodine receptor is an intracellular calcium release channel which plays a central role in excitation contraction coupling. At least 80 mutations have been identified in the gene encoding the skeletal muscle ryanodine receptor and linked to several neuromuscular disorders, whose common feature appears to be a dysregulation of calcium homeostasis. A decade of research into the functional consequences of how these mutations affect the functional properties of the ryanodine receptor and their impact on disease, have significantly advanced our understanding of Malignant Hyperthermia, Central Core Disease and Multiminicore Disease.

Effect of cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum Ca-ATPase, on skeletal muscles from normal and mdx mice.

Aim: In this study, we investigated Ca2+ loading by the sarcoplasmic reticulum in skeletal muscle from mdx mice, an animal model of human Duchenne's muscular dystrophy, at two stages of development: 4 and 11 weeks.

Method: Experiments were conducted on fast- (extensor digitorum longus, EDL) and slow- (soleus) twitch muscles expressing different isoforms of Ca2+-ATPase, which is responsible for the uptake of Ca2+ by the sarcoplasmic reticulum.

Results: In sarcoplasmic reticulum vesicles, the ATP-dependent activity and sensitivity to cyclopiazonic acid (CPA), an inhibitor of the sarcoplasmic reticulum Ca2+-ATPase, were similar in mdx and normal EDL muscle.

Sarcoplasmic reticulum function in slow- and fast-twitch skeletal muscles from mdx mice.

The aim of the present study was to establish whether alterations in sarcoplasmic reticulum function are involved in the abnormal Ca(2+) homeostasis of skeletal muscle in mice with muscular dystrophy ( mdx). The properties of the sarcoplasmic reticulum and contractile proteins of fast- and slow-twitch muscles were therefore investigated in chemically skinned fibres isolated from the extensor digitorum longus (EDL) and soleus muscles of normal (C57BL/10) and mdx mice at 4 and 11 weeks of development. Sarcoplasmic reticulum Ca(2+) uptake, estimated by the Ca(2+) release following exposure to caffeine, was significantly slower in mdx mice, while the maximal Ca(2+) quantity did not differ in either type of skeletal muscle at either stage of development.

Sarcoplasmic reticulum Ca(2+) content affects 4-CmC and caffeine contractures of rat skinned skeletal muscle fibers.

This study investigated whether the sarcoplasmic reticulum Ca(2+) content of rat skeletal muscle fibers affected contractile responses obtained by an application of 4-chloro-m-cresol (4-CmC) and caffeine. Contractures were elicited on saponin-skinned fibers under different Ca(2+) loading conditions. The amplitude of 4-CmC and caffeine contractures of fast-twitch muscle fibers (edl, extensor digitorum longus) differed between the different loading conditions, and this is associated with a greater change in sensitivity to 4-CmC.