RAPID RECOVERY FOLLOWING CONTRACTION-INDUCED INJURY TO IN-SITU SKELETAL-MUSCLES IN MDX MICE

The muscles of mdx mice lack the subsarcolemmal protein dystrophin, an d as a consequence may be more susceptible to damage induced by contra ctions. The purpose of this study was to characterize the response of muscles in mdx mice to contraction-induced injury in The hypothesis te sted was that following a protocol of repeated stretches of maximally situ. activated muscles, the magnitude of the injury is greater for mu scles in mdx mice than for muscles in C57BL/10 control mice, and conse quently, the muscles in mdx mice recover more slowly. Each stretch was of 20% strain relative to muscle fibre length (L-f) at 0.5 L-f s(-1) and was initiated from the force plateau of an isometric contraction. The protocol consisted of a total of ten contractions, with one contra ction occurring every ten seconds. The time-course of injury and recov ery was determined through measurements of in situ force production at 10, 30, 45 and 60 minutes, and either 12, 24, 48 or 72 hours after th e contraction protocol. The initial injury, as assessed by the decreas e in force production both immediately and 60 minutes after the contra ction protocol, was significantly greater for the muscles in mdx mice compared with those in control mice. Over the next three days, a value for maximum isometric force of similar to 80% of the pre-injury value was maintained for muscles in control mice, whereas within three days muscles in mdx mice showed complete recovery of force. For muscles in mice, the mdx greater decrease in force during the contraction protoc ol and the more rapid recovery indicates an increased susceptibility t o contraction-induced injury but an enhanced rate of recovery. (C) Cha pman & Hall Ltd.