THE EFFECTS OF TEMPERATURE AND pH ON THE CONTRACTILE PROPERTIES OF SKINNED MUSCLE

1. Fibre types in the iliofibularis muscle of the freshwater terrapin Pseudemys scripta elegans have been characterized on the basis of their histochemical characteristics, nerve endings and contractile properties. Three types of focally innervated fibres are present, corresponding to the fast glycolytic (Fg), fast oxidative glycolytic (FOG) and slow oxidative (SO) fibre types of other vertebrates. 2. Single fibres or small bundles of fibres representing each histochemical type were identified on the basis of their light scattering properties under dark-field illumination. Fibres were detergent-skinned using Brij 58, and their maximum isometric tension (Po) and unloaded contraction velocity (Vo) were determined by the slack test method. At 15 °C, fast glycolytic fibres generated maximum isometric tensions of 184±5kNm~2 and Vo values of 5-5 ± 0-3 muscle lengths per second (Los~'). Slow oxidative fibres produced tensions of 70-6±3kNm~2 and had Vo values of 1-3 Los~'. Tensions and Vo values of fast oxidative glycolytic fibres were between those of Fg and SO fibres. 3. The force-velocity (P—V) characteristics of slow oxidative fibres were studie