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Malformed mdx myofibers have normal cytoskeletal architecture yet altered EC coupling and stress-induced [Ca.sup.2+] signaling
- Source :
- The American Journal of Physiology. Sept, 2009, Vol. 297 Issue 3, pC571, 10 p.
- Publication Year :
- 2009
-
Abstract
- Skeletal muscle function is dependent on its highly regular structure. In studies of dystrophic (dy/dy) mice, the proportion of malformed myofibers decreases after prolonged whole muscle stimulation, suggesting that the malformed myofibers are more prone to injury. The aim of this study was to assess morphology and to measure excitation-contraction (EC) coupling ([Ca.sup.2+] transients) and susceptibility to osmotic stress ([Ca.sup.2+] sparks) of enzymatically isolated muscle fibers of the extensor digitorum longus (EDL) and flexor digitorum brevis (FDB) muscles from young (2-3 mo) and old (8-9 mo) mdx and age-matched control mice (C57BL10). In young mdx EDL, 6% of the myofibers had visible malformations (i.e., interfiber splitting, branched ends, midfiber appendages). In contrast, 65% of myofibers in old mdx EDL contained visible malformations. In the mdx FDB, malformation occurred in only 5% of young myofibers and 11% of old myofibers. Age-matched control mice did not display the altered morphology of mdx muscles. The membrane-associated and cytoplasmic cytoskeletal structures appeared normal in the malformed mdx myofibers. In mdx FDBs with significantly branched ends, an assessment of global, electrically evoked [Ca.sup.2+] signals (indo-1PE-AM) revealed an EC coupling deficit in myofibers with significant branching. Interestingly, peak amplitude of electrically evoked [Ca.sup.2+] release in the branch of the bifurcated mdx myofiber was significantly decreased compared with the trunk of the same myofiber. No alteration in the basal myoplasmic [Ca.sup.2+] concentration (i.e., indo ratio) was seen in malformed vs. normal mdx myofibers. Finally, osmotic stress induced the occurrence of [Ca.sup.2+] sparks to a greater extent in the malformed portions of myofibers, which is consistent with deficits in EC coupling control. In summary, our data show that aging mdx myofibers develop morphological malformations. These malformations are not associated with gross disruptions in cytoskeletal or t-tubule structure; however, alterations in myofiber [Ca.sup.2+] signaling are evident. calcium; muscular dystrophy; skeletal muscle
- Subjects :
- Animal experimentation -- Usage
Animal experimentation -- Methods
Calcium channels -- Physiological aspects
Calcium channels -- Research
Muscular dystrophy -- Care and treatment
Muscular dystrophy -- Research
Muscles -- Physiological aspects
Muscles -- Structure
Muscles -- Research
Biological sciences
Subjects
Details
- Language :
- English
- ISSN :
- 00029513
- Volume :
- 297
- Issue :
- 3
- Database :
- Gale General OneFile
- Journal :
- The American Journal of Physiology
- Publication Type :
- Academic Journal
- Accession number :
- edsgcl.208640506