Acetylcholinesterase in cocultures of rat myotubes and spinal cord neurons: effects of collagenase and cis-hydroxyproline on molecular forms, intra- and extracellular distribution, and formation of patches at neuromuscular contacts.

Cultures of rat myotubes from 18-day-old embryos produce both globular (G) and asymmetric (A) forms of acetylcholinesterase (AChE; EC 3.1.1.7), mostly G1, G4, and A12 and a small proportion of A8. We show that all forms are partly intracellular and partly exposed to the extracellular medium; the A forms and their intra- and extracellular distribution are not modified when myotubes are grown in the presence of spinal cord neurons. In these cocultures, however, AChE patches may be detected immunohistochemically at sites of neuromuscular contacts. These patches represent a very minor proportion of AChE activity. We found that collagenase removes AChE patches but not the acetylcholine receptor clusters with which they coincide. This digestion specifically decreases the level of the A12 form. cis-Hydroxyproline, an inhibitor of collagen synthesis, reduces the level of G1 and blocks the synthesis of A forms.