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Regulation of acetylcholine release by muscarinic receptors at the mouse neuromuscular junction depends on the activity of acetylcholinesterase
Author(s) -
Minic Jasmina,
Molgó Jordi,
Karlsson Evert,
Krejci Eric
Publication year - 2002
Publication title -
european journal of neuroscience
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.346
H-Index - 206
eISSN - 1460-9568
pISSN - 0953-816X
DOI - 10.1046/j.0953-816x.2001.01875.x
Subject(s) - muscarine , muscarinic acetylcholine receptor , acetylcholine , methoctramine , pertussis toxin , acetylcholinesterase , muscarinic acetylcholine receptor m2 , muscarinic acetylcholine receptor m3 , chemistry , neuromuscular junction , acetylcholine receptor , muscarinic acetylcholine receptor m1 , muscarinic acetylcholine receptor m5 , endocrinology , biophysics , receptor , medicine , neuroscience , biology , g protein , biochemistry , enzyme
Muscarinic acetylcholine receptors (mAChRs) play an important role in regulating the release of acetylcholine (ACh) in various tissues. We used subtype‐specific antibodies and a fluorescent‐labelled muscarinic toxin to demonstrate that mammalian neuromuscular junction expresses mAChR subtypes M 1 to M 4 , and that localization of all subtypes is highly restricted to the innervated part of the muscle. To elucidate the roles of the mAChR subtypes regulating ACh release, we measured the mean quantal content of endplate potentials in isolated mouse phrenic–hemidiaphragm preparations in which release was reduced by a low Ca 2+ /high Mg 2+ medium. Muscarine decreased evoked ACh release in normal junctions but, depending on the concentration, reduced or increased transmitter release in collagen Q‐deficient junctions completely lacking acetylcholinesterase (AChE). Both effects were also seen in normal junctions when AChE was inhibited by various doses of fasciculin‐2. Block of mAChRs by atropine had no effect on evoked release at normal junctions, but decreased release at junctions lacking AChE. The muscarine‐elicited depression of ACh release in normal junctions was completely abolished by pertussis toxin or methoctramine pretreatment, but was not affected by muscarinic toxin MT‐3, thus indicating the involvement of the M 2 mAChR. The muscarine‐induced increase of ACh release in AChE‐deficient junctions was not affected by pertussis toxin, but was completely blocked by MT‐7, a specific M 1 mAChR antagonist. Our results show that the M 1 and M 2 mAChRs have opposite presynaptic functions in modulating quantal ACh release, and that regulation of release by the two receptor subtypes depends on the functional state of AChE at the neuromuscular junction.