Cholinesterases and the resistance of the mouse diaphragm to the effect of tubocurarine.
BACKGROUND
The diaphragm is resistant to competitive neuromuscular blocking agents. Because of the competitive mechanism of action of tubocurarine, the rate of hydrolysis of acetylcholine at the neuromuscular junction may modulate its neuromuscular blocking effect. The authors compared the neuromuscular blocking effect of tubocurarine on isolated diaphragm and extensor digitorum longus (EDL) muscles and quantified the acetylcholinesterase activity in hetero-oligomers.


METHODS
Adult Swiss-Webster and collagen Q-deficient (ColQ) mice were used. The blocking effect of tubocurarine on nerve-evoked muscle twitches was determined in isolated diaphragm and EDL muscles, after inhibition of acetylcholinesterase by fasciculin-1, butyrylcholinesterase by tetraisopropylpyro-phosphoramide, or both acetylcholinesterase and butyrylcholinesterase by neostigmine, and in acetylcholinesterase-deficient ColQ muscles. The different acetylcholinesterase oligomers extracted from diaphragm and EDL muscles were quantified in sucrose gradient.


RESULTS
The EC50 for tubocurarine to decrease the nerve-evoked twitch response was four times higher in the diaphragm than in the EDL. The activity of the different acetylcholinesterase oligomers was lower in the diaphragm as compared with the EDL. Inhibition of acetylcholinesterase by antagonists resulted in an increased dose of tubocurarine but an unchanged resistance ratio between the diaphragm and the EDL. A similar diaphragmatic resistance was found in ColQ muscles.


CONCLUSIONS
The current study indicates that, despite differences in acetylcholinesterase activity between the diaphragm and EDL, the diaphragmatic resistance to tubocurarine cannot be explained by the different rate of acetylcholine hydrolysis in the synaptic cleft.
Nguyen-Huu
Tu
T
Laboratoire de Neurobiologie Cellulaire et Moléculaire, Unité Propre de Recherche 9040, Centre National de la Recherche Scientifique, Gif-sur-Yvette cedex, France.
Dobbertin
Alexandre
A
Barbier
Julien
J
Minic
Jasmina
J
Krejci
Eric
E
Duvaldestin
Philippe
P
Molgó
Jordi
J
D000110:Acetylcholinesterase / Q000502:physiology*; D000818:Animals; D003094:Collagen / Q000502:physiology*; D003964:Diaphragm / Q000187:drug effects* / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D066298:In Vitro Techniques; D051379:Mice; D009124:Muscle Proteins / Q000502:physiology*; D009469:Neuromuscular Junction / Q000187:drug effects; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology*; D011978:Receptors, Nicotinic / Q000032:analysis; D014403:Tubocurarine / Q000494:pharmacology*
D009124:Muscle Proteins; D003473:Neuromuscular Nondepolarizing Agents; D011978:Receptors, Nicotinic; D003094:Collagen; D000110:Acetylcholinesterase; D014403:Tubocurarine