Fibrillation potentials do not originate in type 1 muscle fibers?

Electrophysiological and muscle histochemical studies of denervated muscle were performed simultaneously in order to determine the relationship between fibrillation potentials and muscle fiber type. Fibrillation potentials recorded in the soleus muscle 2 weeks after resection of the sciatic nerve revealed a lower firing rate than in the extensor digitorum longus (EDL) muscle of the same rats. The majority of muscle fibers stained for adenosine triphosphatase (ATPase) activity after preincubation at pH 9.4, 4.6, and 4.3 in the soleus muscle were type 1 fibers, while most of those in the EDL were of type 2. Moreover, one of the rats, which demonstrated no fibrillation potentials in the soleus muscle, was found to have no type 2A or 2B fibers histochemically, in the same soleus muscle. These findings suggest that fibrillation potentials may not originate in type 1 fibers.