Contraction enhancement in skeletal muscles of normal and dystrophic mice

¹ Department of Rehabilitation Medicine, State University of New York, Downstate Medical Center, Brooklyn, New York

Effects of NO₃^–, 1 mm caffeine, and 0.1 mm Zn⁺⁺ on tension output of excised, curarized normal and dystrophic mouse gastrocnemius muscles have been studied. NO₃^– increased twitch tension in normal muscles to 133% of control values and in dystrophic muscles to 177%. It also increased tetanus tension in dystrophic muscles to 126% of control values without affecting tetanus tension of normal muscles. Twitch duration shortened and twitch speed increased in both muscle groups. Caffeine increased twitch and tetanus tensions to 120 and 114% of control values, respectively, in normal muscles, and to 129 and 113% in dystrophic muscles. Twitch durations increased slightly. Both agents reduced tetanus fusion frequency. Zn⁺⁺ did not affect either muscle group. Thus, NO₃^– and caffeine extend the duration of the active state plateau in normal and dystrophic muscles. NO₃^– also intensifies the active state but only in dystrophic muscles, while caffeine does so in both groups. The pronounced effect of NO₃^– on dystrophic muscles suggests a derangement of Ca⁺⁺ sites in the diseased membrane.

Key Words: NO₃^– • caffeine • Zn⁺⁺ • active state properties • membrane properties

Submitted on July 6, 1964

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