Biomechanics of the sarcolemma and costameres in single skeletal muscle fibers from normal and dystrophin-null mice
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We studied the biomechanical properties of the sarcolemma and its links through costameres to the contractile apparatus in single mammalian myofibers of Extensor digitorum longus muscles isolated from wild (WT) and dystrophin-null (mdx) mice. Suction pressures (P) applied through a pipette to the sarcolemma generated a bleb, the height of which increased with increasing P. Larger increases in P broke the connections between the sarcolemma and myofibrils and eventually caused the sarcolemma to burst. We used the values of P at which these changes occurred to estimate the tensions and stiffness of the system and its individual elements. Tensions of the whole system and the sarcolemma, as well as the maximal tension sustained by the costameres, were all significantly lower (1.8–3.3 fold) in muscles of mdx mice compared to WT. Values of P at which separation and bursting occurred, as well as the stiffness of the whole system and of the isolated sarcolemma, were ~2-fold lower in mdx than in WT. Our results indicate that the absence of dystrophin reduces muscle stiffness, increases sarcolemmal deformability, and compromises the mechanical stability of costameres and their connections to nearby myofibrils.
KeywordsMuscle mechanics Costamere mdx Superficial tension Dystrophic muscle Muscular dystrophy
This research was partially supported by grants to R. J. Bloch from the National Institute of Heath (5R01AR055928) and the Muscular Dystrophy Association. K. P. García-Pelagio was supported during the Ph. D. program (Doctorado en Ciencias Biomédicas, Universidad Nacional Autónoma de México) by a scholarship from Consejo Nacional de Ciencia y Tecnología.
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