Reduced release probability prevents vesicle depletion and transmission failure at dynamin mutant synapses.
Endocytic recycling of synaptic vesicles after exocytosis is critical for nervous system function. At synapses of cultured neurons that lack the two "neuronal" dynamins, dynamin 1 and 3, smaller excitatory postsynaptic currents are observed due to an impairment of the fission reaction of endocytosis that results in an accumulation of arrested clathrin-coated pits and a greatly reduced synaptic vesicle number. Surprisingly, despite a smaller readily releasable vesicle pool and fewer docked vesicles, a strong facilitation, which correlated with lower vesicle release probability, was observed upon action potential stimulation at such synapses. Furthermore, although network activity in mutant cultures was lower, Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) activity was unexpectedly increased, consistent with the previous report of an enhanced state of synapsin 1 phosphorylation at CaMKII-dependent sites in such neurons. These changes were partially reversed by overnight silencing of synaptic activity with tetrodotoxin, a treatment that allows progression of arrested endocytic pits to synaptic vesicles. Facilitation was also counteracted by CaMKII inhibition. These findings reveal a mechanism aimed at preventing synaptic transmission failure due to vesicle depletion when recycling vesicle traffic is backed up by a defect in dynamin-dependent endocytosis and provide new insight into the coupling between endocytosis and exocytosis.
Department of Cell Biology, Howard Hughes Medical Institute, Program in Cellular Neuroscience, Neurodegeneration and Repair, Kavli Institute for Neuroscience, Yale University School of Medicine, New Haven, CT 06510, USA. xlou3@wisc.edu
Xuelin
X
Lou
Fan
F
Fan
Mirko
M
Messa
Andrea
A
Raimondi
Yumei
Y
Wu
Loren L
LL
Looger
Shawn M
SM
Ferguson
Pietro
P
De Camilli
D000818:Animals; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000378:metabolism; D002540:Cerebral Cortex / Q000473:pathology; D034281:Dynamins / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation / Q000235:genetics*; D009474:Neurons / Q000378:metabolism; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000201:enzymology / Q000378:metabolism* / Q000648:ultrastructure; D015854:Up-Regulation
D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D034281:Dynamins