Nerve regulation of class I and Class II‐asymmetric forms of acetylcholinesterase in rat skeletal muscles

Two classes of collagen‐tailed, asymmetric forms (A‐forms) of acetylcholinesterase (AChE) have been described in skeletal muscles of vertebrates. They are distinguished by their different solubilization requirements: class I A‐forms are solubilized in the presence of high salt, whereas class II A‐forms require in addition a chelating agent for solubilization. We report here that class II A‐forms are less sensitive to nerve section than are class I A‐forms. The latter form decreases faster and to a lower level of activity after denervation. The decay of both AChE classes is more rapidly in short‐stump nerves than in long ones. The effect of nerve section on class II A‐forms appears to be dependent on the particular muscle group being studied. Both classes of A‐forms reappear after muscle reinnervation, but the class I A‐forms recovered earlier. More interestingly, both classes of A‐forms increase in normally innervated skeletal muscles after contralateral nerve injury. In this case, however, the class II A‐forms change first. Muscular disuse induced by contralateral tenotomy is also followed by a rise in class II A‐forms. Our results, showing differences in response and flexibility in the changes of the two classes of A‐forms in several experimental conditions, represent a relevant contribution to the understanding of the regulation and functional role of the asymmetric forms of AChE in vertebrate skeletal muscles.