ELECTRONMICROSCOPIC LOCALIZATION OF CHOLINESTERASE AT NEUROMUSCULAR JUNCTION BY A QUATERNARY CARBON ANALOGUE OF ACETYLTHIOCHOLINE AS SUBSTRATE

By means of a quaternary carbon analogue of acetylthiocholine (AThCh)' 3,3-dimethylbuthylthioacetate (DMBTA) as a substrate for cholinesterase (ChE), acethylcholinesterase (AChE) has been localized at the neuromuscular junctions of the rat diaphragm in an electron microscope histochemical investigation. AChE is associated with the pre- and postsynaptical membranes, with much greater activity at the latter. Enzymatic activity is not found within the junctional clefts, nor in association with the synaptic vesicles of the axonal end arborization. The lack of AChE in association with the vesicles is regarded as particularly important, since DMBTA due to its electroneutrality probably penetrate biological membranes more easily than charged substrates employed so far. © 1969 Springer-Verlag.