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 dig itorum longus muscle: sciatic nerve transection (group A) and sciatic nerve crush allowing further reinnervation (group B). Contractile resp onses were then studied at different times after the denervation (7, 1 4, 30, and 60 days) and compared with control. Sixty days after the in tervention, twitch and tetanic tensions remained dependent upon the ex tracellular Ca2+ concentration ([Ca](o)) both in groups A and B. Howev er, the depression of tensions following Ca2+ withdrawal was more impo rtant in group A. Sixty days after birth, in the presence of a Ca2+ ch annel blocker, Cd2+ (2 mmol L(-1)), a depression of the twitch tension was observed in group A (similarly to control 1-7 days postnatal musc les), whereas Cd2+ potentiated twitch tension in group B (similarly to control 14-60 days postnatal muscles). After glycerol treatment (detu bulating procedure) performed in 60-day-old muscles, twitch tension wa s abolished in group B and control, whereas twitch tension was potenti ated in group A. Thus, in developing muscles, neural control could be involved in the dependence of contractility toward [Ca](o). These resu lts may be relevant for the understanding of the contractile propertie s of neuromuscular disorders with early onset, (C) 1996 John Wiley & S ons, Inc.