Cholinesterases of neuromuscular junction

The ultrastructural localization of AChE and BuChE was studied in motor endplates of the rat and mouse diaphragms, using the CNS(?) modification of the one-step Cu-thiocholine procedure. AChE activity was observed on pre- and postsynaptic membranes, in the basal lamina and in the Schwann cell-nerve terminal interspace. The localization of BuChE was similar but much less pronounced in the adult muscle, while for the developing muscle, the reverse was true. In developing motor endplates and in endplates of rats after irreversible inhibition of AChE where synthesis de novo is enhanced, AChE activity in the endoplasmic reticulum and perinuclear membrane of the Schwann cell and in the sarcoplasmic reticulum was pronounced, indicating that junctional AChE may be synthesized at these sites. AChE and BuChE have a similar localization, mode of attachment and molecular forms. A possible mechanism underlying these similarities is discussed.