Extrajunctional resting Ca2+ influx is not increased in a severely dystrophic expiratory muscle (triangularis sterni) of the mdx mouse.

Freshly isolated adult mdx and nondystrophic (C57B110SnJ) muscle fibers were used to examine the potential role of resting Ca2+ influx in the pathogenesis of Duchenne and related dystrophies. Microfluorimetric determinations of resting divalent cation influx were obtained from undissociated intact muscle fibers in the triangularis sterni (TS), a thin expiratory muscle. Morphological evidence indicated severe dystrophic alterations in the mdx TS at 5 months, and a pronounced loss of fibers with connective tissue infiltration in older animals.