Effect of dystrophin loss of myofiber function and organization. (A) Normal myofiber and (B) dystrophin-deficient mdx myofiber. Dystrophin and associated proteins are normally found at the rib-like costameres linking sarcomeric Z bands with the plasma membrane. Loss of dystrophin results in disorganized costameres and enhanced membrane leak. Increased edema and inappropriate cytosolic Ca2+ and ROS generation (filled circles and diamonds) contribute further to muscle dysfunction. Increased extracellular matrix deposition surrounding myofibers also occurs and perturbs membrane integrity. This interaction is particularly important during muscle contraction.