Localization of the pool of G4 acetylcholinesterase characterizing fast muscles and its alteration in murine muscular dystrophy

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Abstract
The distributions of acetylcholinesterase and its molecular forms within muscles of normal and dystrophic 129/ReJ mice were established by a concomitant cytochemical and biochemical study performed on 1‐mm serial sections of three predominantly fas muscles, i.e., anterior tibialis, extensor digitorum longus, and sternomastoid, as well as the slow‐twitch soleus. This comparative study showed the following main finding.(1)In every muscle of bothe normal and dystrophic mice (a) the three asymmetric forms were confined to the motor zone where they systematically codistributed with the endplates, and (b) all globular forms, including G4, were concentrated at the motro zone from which they extended over the entrie muscle length along a concentration gradient. (2) In the normal muscles, the perijunctional sarcoplasmic cytochemical reaction exhibited by individual fibers was grouped into a well‐defined conjunctional acetylcholinesterase compartment in which the endplates were embedded. The overall intensity of the cojunctinal cytochemical reaction was either high or low according to whether the muscle was predominantly fast or slow. (3) This conjuncitonal acetylcholinesterase compartment varied in close parallelism with G4 and thus appeared as the cytochemical correlate of the G4 molecules concentrated around the endplates. In particular, as the shape of the motor zone progressively increased in complexity along with the intricacy of the muscle fiber organization, from sternomastoid to extensor digitorum longus to anterior tibialis, so did both the relative volume occupied by the cojunctional acetylcholinesterase compartment and the proportion of G4. (4) The motor zone of the normal fast‐twitch muscles characteristically differed from that of the soleus by the presence of a G4‐rich enviornment around the endplates, which was cooperatively provided by the the surrounding fibers. (5) In dystrophic muscles, this cojunctinal G4‐rich compartment was lost: the cytochemical compartment was no longer discernable, while G4 was reduced to a minimal low level similar to that characteristic of the normal soleus.

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