Acetylcholinesterase in the neuromuscular junction.

New findings regarding acetylcholinesterase (AChE) in the neuromuscular junction (NMJ), obtained in the last decade, are briefly reviewed. AChE is highly concentrated in the NMJs of vertebrates. Its location remains stable after denervation in mature rat muscles but not in early postnatal muscles. Agrin in the synaptic basal lamina is able to induce sarcolemmal differentiations accumulating AChE even in the absence of a nerve ending. Asymmetric A12 AChE form is the major molecular form of AChE in vertebrate NMJs. Extrajunctional suppression of this form is a developmental phenomenon. Motor nerve is able to reinduce expression of the A12 AChE form in the ectopic NMJs even in muscles with complete extrajunctional suppression of this form. The 'tail' of the A12 AChE form is made of collagen Q. It contains domains for binding AChE to basal lamina with ionic and covalent interactions. Muscle activity is required for normal AChE expression in muscles and its accumulation in the NMJs. In addition, the pattern of muscle activation also regulates AChE activity in the NMJs, demonstrating that the pattern of synaptic transmission is able to modulate one of the key synaptic components.