Tetanic Force and Shortening in Locust Flight Muscle

Abstract

1. The maximum tetanic force and shortening was studied in the isolated, dorsal-longitudinal muscle of the hindwings of the desert locust (Schistocerca gregaria). 2. The muscle tended to die when isolated in artificial salines but after penicillin had been added it survived well for more than 8 hr. at 32° C. The cause is discussed. 3. The flight muscle is very sensitive to lack of oxygen and, at room temperature and above, it is necessary to perfuse the main tracheae with air. No difference was observed between indirect and direct stimulation. 4. The natural activity consists of repetitive twitches. Tetanic contractions always caused rapid fatigue and tended to injure the muscle, partly because of excessive shortening (‘delta state’) and partly because the muscle ‘gave’ at the comparatively small total tension of 2-2.5 kg.cm.^-2. 5. The length-force diagram at 11°C. resembles that of ordinary skeletal muscle, but the maximum shortening (0.45L_b) and the maximum isometric tension (1.6 kg.cm.^-2) are smaller than in frog muscle at that temperature. As in mammalian muscle, the isometric tension increases much with temperature and was estimated indirectly as 3 kg.cm.^-2 at 25°C. and 4 kg.cm.^-2 at 35°C. The largest observed shortening was 0.55L_b. At ordinary body temperature, tension and work are of the same magnitude as in skeletal muscle of vertebrates. 6. The flight muscle is less extensible than frog muscle and the maximum isometric force is produced at a lower I-band/sarcomere ratio (0.2). 7. As in frog muscle, passive stretch only affects the I-bands, while the A-bands remain at constant length, at least in the fixed material used here. 8. It is probable that the mechanical specialization of the flight muscle mainly concerns the sarcolemma and the other passive-elastic elements; the contractile elements do not seem to differ from ordinary muscle.