SPECIFIC IMPULSE PATTERNS REGULATE ACETYLCHOLINESTERASE ACTIVITY IN SKELETAL-MUSCLES OF RATS AND RABBITS

In rats, acetylcholinesterase (AChE) activity in the fast muscles is s everal times higher than in the slow soleus muscle, The hypothesis tha t specific neural impulse patterns in fast or slow muscles are respons ible for different AChE activities was tested by altering the neural a ctivation pattern in the fast extensor digitorum longus (EDL) muscle b y chronic low-frequency stimulation of its nerve, In addition, the sol eus muscle was examined after hind limb immobilization, which changed its neural activation pattern from tonic to phasic, Myosin heavy-chain (MHC) isoforms were analyzed by gel electrophoresis. Activity of the molecular forms of AChE was determined by velocity sedimentation, Low- frequency stimulation of the rat EDL for 35 days shifted the profile o f MHC II isoforms toward a slower MHCIIa isoform, Activity of the glob ular G(1) and G(4) molecular forms of AChE decreased by a factor of 4 and 10, respectively, and became comparable with those in the soleus m uscle, After hind limb immobilization, the fast MHCIId isoform, which is not normally present, appeared in the soleus muscle, Activity of th e globular G(1) form of AChE increased approximately three times and a pproached the levels in the fast EDL muscle, In the rabbit, on the con trary to the rat, activity of the globular forms of AChE in a fast mus cle increased after low-frequency stimulation, The results demonstrate that specific neural activation patterns regulate AChE activity in mu scles, Great differences, however, exist among different mammalian spe cies in regard to muscle AChE regulation. (C) 1997 Wiley-Liss, Inc.