Endplates after esterase inactivation in vivo: correlation between esterase concentration, functional response and...

Area of Science:

• Neuroscience
• Muscle Physiology
• Biochemistry

Background:

• Diisopropylfluorophosphate (DFP) is an irreversible inhibitor of esterases, including acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE).
• Neuromuscular junction function relies on the precise regulation of acetylcholine (ACh) by esterases.
• Inhibition of these esterases can lead to prolonged ACh action and potential muscle dysfunction.

Purpose of the Study:

• To investigate the time course of muscle recovery after DFP-induced esterase inactivation.
• To correlate the recovery of neuromuscular function with the regeneration of AChE and BuChE.
• To elucidate the underlying mechanisms of DFP-induced myopathy.

Main Methods:

• In vivo incubation of mouse sternomastoid muscles with DFP.
• Histochemistry, EM autoradiography, and physiological recordings to assess muscle function and enzyme recovery.
• Assessment of structural changes in muscle fibers.

Main Results:

• DFP-induced esterase saturation eliminated the muscle's ability to sustain tetanus.
• Partial recovery of muscle function was observed with less than 10% AChE recovery.
• A positive correlation was found between AChE recovery extent and the stimulation frequency for sustained tetanic response.
• Myopathy, characterized by Z band dissolution and sarcoplasmic reticulum breakdown, peaked at 3 days and recovered by 2 weeks.
• Myopathy was prevented by nerve cutting or alpha-bungarotoxin inactivation of acetylcholine receptors.

Conclusions:

• DFP-induced myopathy is mediated by prolonged acetylcholine action due to esterase inhibition.
• Calcium (Ca2+) fluxes resulting from sustained ACh activity likely contribute to the observed myopathy.
• AChE recovery is critical for restoring normal neuromuscular function and preventing myopathy.