Cholinesterase is associated with the basal lamina at the neuromuscular junction

TLDR: Direct evidence is presented that junctional ChE is associated with the basal lamina of the synaptic cleft in skeletal muscle, a protein known to be a principal component of BLs.

Abstract: THE cholinesterase (ChE) of skeletal muscle is concentrated at the neuromuscular junction, where it hydrolyses acetylcholine released from the nerve terminal1–5. In frog muscle treated with a histochemical stain for ChE, enzyme activity is demonstrable at all terminal branches of the neuromuscular junction (Fig. 1a), with the reaction product occupying the synaptic cleft between nerve and muscle (Fig. 1d)1,6. A particulate enzyme, ChE was assumed to be integral to the postsynaptic plasma membrane2 until Hall and Kelly7 showed that mild protease treatment of intact muscles released active ChE into the medium without apparent damage to the plasma membrane. One possibility raised by this result is that ChE is associated with the basal lamina (BL; sometimes called basement membrane) that runs through the synaptic cleft8. This idea was supported by the finding that a subunit of ChE from electric organs of fishes and rays has several properties in common with collagen9–11, a protein known to be a principal component of BLs12. Here, we present direct evidence that junctional ChE is associated with the BL of the synaptic cleft in skeletal muscle.