Activity-dependent presynaptic regulation of quantal size at the mammalian neuromuscular junction in vivo.
Changes in synaptic activity alter quantal size, but the relative roles of presynaptic and postsynaptic cells in these changes are only beginning to be understood. We examined the mechanism underlying increased quantal size after block of synaptic activity at the mammalian neuromuscular junction in vivo. We found that changes in neither acetylcholinesterase activity nor acetylcholine receptor density could account for the increase. By elimination, it appears likely that the site of increased quantal size after chronic block of activity is presynaptic and involves increased release of acetylcholine. We used mice with muscle hyperexcitability caused by mutation of the ClC-1 muscle chloride channel to examine the role of postsynaptic activity in controlling quantal size. Surprisingly, quantal size was increased in ClC mice before block of synaptic activity. We examined the mechanism underlying increased quantal size in ClC mice and found that it also appeared to be located presynaptically. When presynaptic activity was completely blocked in both control and ClC mice, quantal size was large in both groups despite the higher level of postsynaptic activity in ClC mice. This suggests that postsynaptic activity does not regulate quantal size at the neuromuscular junction. We propose that presynaptic activity modulates quantal size at the neuromuscular junction by modulating the amount of acetylcholine released from vesicles.
Wang
Xueyong
X
Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Li
Yingjie
Y
Engisch
Kathrin L
KL
Nakanishi
Stan T
ST
Dodson
Sara E
SE
Miller
Gary W
GW
Cope
Timothy C
TC
Pinter
Martin J
MJ
Rich
Mark M
MM
D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D018118:Chloride Channels / Q000235:genetics / Q000502:physiology; D004576:Electromyography; D004594:Electrophysiology; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D009043:Motor Activity / Q000502:physiology; D009045:Motor Endplate / Q000502:physiology; D009124:Muscle Proteins / Q000235:genetics / Q000502:physiology; D009469:Neuromuscular Junction / Q000502:physiology*; D018408:Patch-Clamp Techniques; D017729:Presynaptic Terminals / Q000502:physiology*; D011950:Receptors, Cholinergic / Q000378:metabolism; D013572:Synaptic Vesicles / Q000502:physiology*
C086321:CLC-1 channel; D018118:Chloride Channels; D009124:Muscle Proteins; D011950:Receptors, Cholinergic; D000110:Acetylcholinesterase