Coexistence of fast and slow types of myosin light chains in a single fiber of rat soleus muscle

Single muscle fibers were isolated from soleus and extensor digitorum Iongus muscle of adult rats. The muscle fiber type of single fibers was determined physiologically by the skinned fiber method according to the sensitivity to strontium (Sr) ions. The fiber type of single fibers was contrasted to the pattern of myosin light chains ana-lyzed by one and two dimensional gel-electrophoreses. All the type 2 fibers isolated from soleus muscle contained both fast and slow types of myosin light chains. We have been studying the physiological and biochemical properties of single fibers prepared from normal and pathological muscles. During the course of the study, we found that type 2 fibers of soleus muscle in normal adult rats con-tained a hybrid form of myosin light chains. The biological significance of this observation is dis-cussed. Extensor digitorum Iongus (EDL) and soleus muscle were excised in toto from 10-week-old male Wistar rats after decapitation. Muscles were placed and chemically skinned in ice-cold relaxing solution containing 5 IDM EGTA, 4 mM disodiu