Acetylcholinesterase of the motor endplate and its response to muscle denervation.

In innervated and denervated sternohyoid muscles of adult mice the AChE with a pH optimum at 7.2 was shown to occur in all three fiber types in two separate structural areas located: extrafibrillarly (synaptic cleft, postsynaptic folds, subsarcolemmal vesicles, T-tubules, interfibrillar space) and intrafibrillarly (perinuclear cisternae, SR including SR cisternae). There is not a stable connection between the two areas. The functional significance of the intrafibrillar AChE, in particular, is unknown. After muscle denervation, intrafibrillar AChE of the A and B fibers disappears more quickly than that of C fibers. This phenomenon not only suggests a general, but possibly also a fiber-specific neurotrophic effect.