Potentiation of contraction in some insect skeletal muscles—The effect of uranyl acetate

Abstract

1. 1. Twitch and tetanus responses of locust and stick insect leg muscles were recorded isometrically during perfusion with salines containing 0·5 mM/l uranyl acetate. 2. 2. Uranyl acetate ions caused a potentiation of twitch tension of the order of 200 per cent. Peak tetanus tension was also potentiated, but to a lesser degree. 3. 3. Uranyl acetate ions induced a prolongation of the twitch time course particularly in locust muscle, and the muscles entered a slight contracture which lasted the duration of the uranyl acetate treatment. 4. 4. Uranyl acetate ions caused an increase in the rate of tension development in both insect muscles, but there was no observable effect on tetanus fusion frequency. 5. 5. Removal of calcium ions during uranyl acetate treatment resulted in a reversal of potentiation. From this evidence it is concluded that uranyl acetate ions exert their potentiating effects via the muscle calcium release mechanism. 6. 6. It is argued that uranyl acetate ions may well act by inhibiting or delaying the reactivation of the calcium pump of the sarcoplasmic reticulum.