Decreased synaptic activity shifts the calcium dependence of release at the mammalian neuromuscular junction in vivo.
We examined the mechanism underlying increased quantal content after block of activity at the mouse neuromuscular junction in vivo. We found that, when quantal content was measured in solution containing normal extracellular calcium, block of activity had no effect on either quantal content or the response to repetitive stimulation. However, when quantal content was measured in low extracellular calcium, there was a large increase in quantal content after block of activity. The increase in quantal content was accompanied by increased depression during repetitive stimulation. The explanation for these findings was that there was a shift in the calcium dependence of release after block of activity that manifested as an increase in probability of release in low extracellular calcium. Block of presynaptic P/Q channels eliminated the increase in probability of release. We propose that activity-dependent regulation of presynaptic calcium entry may contribute to homeostatic regulation of quantal content.
Wang
Xueyong
X
Center for Neurodegenerative Disease, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Engisch
Kathrin L
KL
Li
Yingjie
Y
Pinter
Martin J
MJ
Cope
Timothy C
TC
Rich
Mark M
MM
D000818:Animals; D002118:Calcium / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology; D004594:Electrophysiology; D006706:Homeostasis / Q000502:physiology; D051379:Mice; D009045:Motor Endplate / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation; D009473:Neuronal Plasticity / Q000502:physiology; D009498:Neurotoxins / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D020867:omega-Agatoxin IVA / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015220:Calcium Channels; D009498:Neurotoxins; D018377:Neurotransmitter Agents; D020867:omega-Agatoxin IVA; D013779:Tetrodotoxin; D002118:Calcium