Release of acetylcholinesterase from rat hemidiaphragm preparations stimulated through the phrenic nerve [21]

ACETYLCHOLINESTERASE (AChE; EC 3.1.1.7) is known to be transported rapidly within peripheral motor nerves, both towards and away from nerve cell bodies^1-3. Of the total amount of neural AChE, approximately 15% is mobile, with about 10% moving towards the nerve terminals and about 5% returning towards cell bodies, the remaining 85% of the enzyme being stationary. Since the mean velocity of orthograde transport is about twice that of the retrograde flow, the total flux of enzyme is 3-4 times greater in the distal than in the proximal direction. Although the fate of this transported AChE is not entirely clear, it has recently been shown that some of the distally transported enzyme may never arrive at the nerve terminals, being incorporated into the axolemma at sites all along the neurone^4,5. This axolemmal incorporation is slow, and it seems likely that AChE would accumulate in the terminals unless there were local mechanisms for its removal, such as proteolytic digestion or extrusion from the cell as has been demonstrated in non-neuronal tissue ^6,7. We now offer evidence that AChE is released from nerve terminals in response to nerve stimulation and suggest that this release may be parallel to, but separate from, release of neurotransmitter.