Effects of external calcium on contractile responses in rat extensor digitorum longus muscles after sciatic nerve injury at birth.

Two types of nerve lesions were performed at birth in rat extensor digitorum longus muscle: sciatic nerve transection (group A) and sciatic nerve crush allowing further reinnervation (group B). Contractile responses were then studied at different times after the denervation (7, 14, 30, and 60 days) and compared with control. Sixty days after the intervention, twitch and tetanic tensions remained dependent upon the extracellular Ca2+ concentration ([Ca]o) both in groups A and B. However, the depression of tensions following Ca2+ withdrawal was more important in group A. Sixty days after birth, in the presence of a Ca2+ channel blocker, Cd2+ (2 mmol L-1), a depression of the twitch tension was observed in group A (similarly to control 1-7 days postnatal muscles), whereas Cd2+ potentiated twitch tension in group B (similarly to control 14-60 days postnatal muscles). After glycerol treatment (detubulating procedure) performed in 60-day-old muscles, twitch tension was abolished in group B and control, whereas twitch tension was potentiated in group A. Thus, in developing muscles, neural control could be involved in the dependence of contractility toward [Ca]o. These results may be relevant for the understanding of the contractile properties of neuromuscular disorders with early onset.