Influence of Temperature on Isometric Contractions of Rat Skeletal Muscles

Abstract

THE influence of temperature on isometric contractions of rat skeletal muscles in vitro has been determined for fast extensor digitorum longus muscles (EDL) and slow soleus muscles (SOL) from 4 week old female Wistar rats. Isometric contractions were recorded with the long axis of the muscle vertical, with one tendon tied to the frame below and the other tendon tied to a short steel wire connexion which linked it with the tension transducer above. The compliance of the transducer (Statham, Gl-80-350) and the steel wire connexion to the muscle was 4.5 × 10⁻⁵ cm/g and the natural frequency of vibration was 2 kHz. The muscle was immersed in about 100 ml. of fluid (137 mM Nacl; 5 mM KCl; 2 mM CaCl₂; 1 mM MgCl₂; 1 mM NaH₂PO₄; 2 g/l. of NaHCO₃ and 2 g/l. of glucose) which was bubbled continuously with 95 per cent O₂ and 5 per cent CO₂. Neuromuscular transmission was blocked by adding 2.0 × 10⁻⁵ g of tubocurarine chloride/ml. of bath fluid. The muscles were stimulated directly by a transverse electrical field of 15 V/cm for 0.2 or 0.3 ms applied to the bath fluid by “massive” bright platinum electrodes set about 1 cm apart¹. All recordings were made with the muscle set at the optimal length determined for twitch contractions at 20° C.