Active state of normal and dystrophic mouse muscle.

Computer-controlled quick releases were used to determine the kinetics of active state tension decay in normal and dystrophic EDL muscles of the mouse (129/Re-J). Also included are measurements of the duration of the active state plateau, isometric twitch and tetanus parameters, and the stress-strain properties of the elastic elements. Alterations in the isometric tension characteristics of dystrophic muscles confirm previous investigations and indicate that dystrophic sarcomeres have a diminished ability to shorten and produce tension. The compliance of the series-elastic elements is not changed, whereas a 50% reduction in the interanl extension of the series elements is noted for dystrophic muscle. The rate of decay and maximum intensity (Po) of active state decay is reduced 60-70% in dystrophic muscles. The first-order rate constant and the total duration of the active state are not altered. These results are discussed in terms of the possible involvement of the contractile proteins and the sarcoplasmic reticulum in determining active state deficits.