Troponin activity of different types of muscle fibers

Abstract

The troponin activity of myosin B from fast-twitch red (R), fast-twitch white (W), and slow-twitch intermediate (I) fibers of guinea pig skeletal muscle was determined, using soleus, semimembranosus proprius, the red part of the vastus lateralis, flexor digitorum longus, medial gastrocnemius, flexor hallucis longus and the white part of the vastus lateralis. The activity is expressed as moles of trypsin-sensitive calcium-binding capacity per gram of myosin B protein. The troponin activity of different skeletal muscles of the same animal differs greatly. The soleus shows the lowest value, and the white part of the vastus lateralis, the highest. A relationship of troponin activity to histochemical fiber type was demonstrated. Intermediate and red fibers have lower troponin activities than white fibers. The discrepancy noted between troponin activities in different fiber types and % ECTA inhibition of Mg-activated ATPase activities may indicate varying proportions of different types of troponin in the different fiber types.