Comparison of the mode of action of succinylcholine and succinylmonocholine on rat skeletal muscle after denervation

The effects of equimolar concentrations (3.0 × 10 −5 M) of succinylcholine (SCh) and succinylmonocholine (SMC) were studied in‐vitro at 20°C in rat extensor digitorum longus muscle (EDL) 0–147 days after common peroneal nerve section. Analysis of simultaneous measurements of K+ efflux (mmolL −1 g −1 ) and contracture tension (mN) to SCh showed that there was a rapid increase in the mean values of both parameters up to 22–28 days after denervation (7.7 mmolL −1 g −1 , 36 mN). At the end of the period studied, the contracture response declined to 4.0 mN whilst the capacity for K+ efflux remained relatively high (4.8 mmolL −1 g −1 ) in comparison with normal contralateral EDL muscle (n = 82) K+ efflux measurements (0.62 mmolL −1 g −1 ). A significant correlation (r = 0.86, P ≤ 0.001) was found between SCh‐induced K+ efflux and contracture tension 1–56 days following nerve section which indicated that the development of the contracture response and K+ efflux were concomitant during the period specified. The ratios of maximum contracture tension/K+ efflux in response to SCh and SMC, 18–22 days after denervation were similar, 4.9 and 5.0, respectively. Results indicated that the mode of action of each agent was similar in denervated rat skeletal muscle, and that they were equally potent in their hyperkalaemic potential. Results of comparative measurements of membrane depolarization and contracture tension in response to SCh and SMC showed that both agents produced quantitatively similar responses at 7 and 14 days after denervation; 23 mN c.f. 20 mN/17 mV c.f. 15 mV, and 32 mN c.f. 33 mN/20 mV c.f. 19 mV, respectively. It is proposed that SMC would not be a suitable substitute for SCh for use with either normal or denervated skeletal muscle.