Synthesis of neuromuscular cholinesterases in innervated and denervated rat diaphragm

Abstract

Quantitative measurements of cholinesterase activity using either acetylcholine (3 m m) in combination with tetramonoisopropylpyrophosphortetramide (10 μ m) or butyrylcholine (3 m m) as substrates have been made in junctional and extrajunctional regions of innervated and denervated rat diaphragm preparations. Acetylcholinesterase activity was highly concentrated in the junctional region and a significant portion was present in the extrajunctional region of the muscle fibers. Butyrylcholinesterase was found evenly distributed in junctional and extrajunctional regions. A significant decrease in the specific activities of acetyl- and butyrylcholinesterase was observed in the junctional and extrajunctional regions 3 days after denervation. After in vivo irreversible inhibition of cholinesterase activity with phospholine (0.2 mg/kg subcutaneously), and organophosphorus compound, acetyl- and butyrylcholinesterase activities were nearly restored in innervated muscle within 7 days after the initial inhibition. In denervated muscle both enzymes recovered to the activities seen in denervated control muscle. The results are discussed in terms of intrinsic muscular control of a part of the junotional cholinesterase activity and the possibility of transsynaptic transport of acetylcholinesterase from the nerve terminal to the postsynaptic membrane.