Recovery of acetylcholinesterase and of its multiple molecular forms in motor end‐plate‐free and motor end‐plate‐rich regions of mouse striated muscle, after irreversible inactivation by an organophosphorus compound (methyl‐phosphorothiolate derivative)

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Abstract
Most of mouse diaphragm muscle acetylcholinesterase (AChE) was irreversibly inhibited after a single i.p. injection of a methylphosphorothiolate derivative (MPT), an organophosphorus compound which phosphorylate the active site. The muscle recovered its AChE (de novo synthesis) and the time course of reappearance of AChE and its multiple active molecular forms was studied. After inhibition, there was an initial (3-15 h) rapid recovery of total AChE (which evolved from 20-28% to 50-60% of the control values), followed by a slow phase of AChE return. After 3 days, the recovery was still incomplete (reaching 70-80% of control values). Among the main molecular forms present in diaphragm muscle (16 S, 10 S and 4 S, accompanied by minor components), the 16 S and 10 S forms were the most sensitive to MPT treatment. During the rapid initial phase of AChE recovery, the absolute rate of recovery of the 4 S form was faster than for the other forms with a correspondingly higher relative proportion to total AChE. These observations were consistent with the hypothesized precursor role of the 4 S. form. The 16 S form, found concentrated in the motor end-plate (MEP)-rich regions and in low amounts in MEP-free regions, was similarly partially recovered in both regions, suggesing that there was 16 S biosynthesis in the MEP-rich regions and in the MEP-free regions.