Contraction enhancement in skeletal muscles of normal and dystrophic mice

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Abstract
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.

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