Raising the antioxidant levels within mouse muscle fibres does not affect contraction‐induced injury

Abstract

A protocol of 75 lengthening contractions (LCP) administered to skeletal muscles of mice causes an initial force deficit owing to the mechanical disruption of sarcomeres and a reduction in calcium release from the sarcoplasmic reticulum. During the 3 days following the LCP, a 'sealing off process' and inflammatory response occurs. The reactive oxygen species (ROS) released by invading inflammatory cells produce a secondary force deficit that is more severe than the initial deficit. The timing of the infiltration of inflammatory cells and increase in force deficit relative to the sealing off process is not well documented. We tested the null hypothesis that following a lifetime of overexpression of the genes for the intracellular antioxidants manganese superoxide dismutase, copper zinc superoxide dismutase or catalase in transgenic mice, the force deficits 3 days following the administration of a 75 LCP to in situ extensor digitorum longus muscles are not different from those of wild-type mice. Following the LCP, the force deficits ranged from 39 to 59% for the muscles of transgenic mice that overexpressed the genes for intracellular antioxidants and were not different from the force deficit of 44% observed for muscles of wild-type mice. The results provide evidence that the ROS damage does not occur within the cytosol of the injured fibres. Apparently, the hypercontraction of sarcomeres and accumulation of vesicles seal off and protect the intact portions of damaged fibres, such that the ROS damage and repair occurs in the milieu of the necrotic segments that are continuous with the extracellular matrix.