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Erik Jorgensen Biology Department, University of Utah Wednesday Nov. 25, 2009 3:05pm in LCB 225 Synaptic vesicle acidification is a checkpoint for vesicle fusion. Abstract: When a synaptic vesicle fuses with the plasma membrane it releases a fixed amount of neurotransmitter. Why? One possibility is that only vesicles that are filled with neurotransmitter are substrates for release. However, mutations in the transporters or biosynthetic enzymes lead to decreases in neurotransmitter release. These data suggest that there is no neurotransmitter checkpoint for vesicle fusion.
Transmitter is loaded into vesicles using secondary active transport,
that is, the vacuolar H+-ATPase pumps protons into the vesicle and
protons are then exchanged for neurotransmitter. Surprisingly,
mutations in the V-ATPase did not decrease the amount of
neurotransmitter. Rather, the frequency of the vesicle fusions was
reduced. Our results are consistent with an acidification checkpoint
whereby only fully acidified synaptic vesicles are competent to
fuse. The uniform neurotransmitter content may be controlled not by a
direct mechanism that monitors neurotransmitter content in a vesicle,
but instead by an indirect mechanism affected by the acidification
state of the vesicle.
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