In:
Annals of the New York Academy of Sciences, Wiley, Vol. 1152, No. 1 ( 2009-01), p. 100-112
Abstract:
In rapid synapses, neurotransmitter quanta are emitted in less than 100 μs, often at a high frequency. Using fast cryofixation of synapses, we found a very brief (2–3 ms) change affecting intramembrane particles in presynaptic membrane. Vesicle openings also occurred but after a significant delay. The particle change is most probably linked to mediatophore, a proteolipid of 220 kDa. Mediatophore aggregates were demonstrated in active zones of the presynaptic membrane. Reconstituted in liposomes, Xenopus oocytes, and neuroblastoma cells, mediatophore releases acetylcholine in a Ca 2+ ‐dependent and quantal manner, mimicking physiological release. In restricted presynaptic “nanodomains,” Ca 2+ concentration explosively reaches a high level and then vanishes with a time constant of 300–400 μs. Among the processes contributing to the fast phase of Ca 2+ buffering, a vesicular Ca 2+ /H + antiport plays a major role. Energized by the Vesicular‐ATPase‐dependent proton gradient, the antiport has a low affinity for Ca 2+ . We inactivated the Ca 2+ /H + antiport using bafilomycin A1, which annihilates the proton gradient. As a result, the postsynaptic potential was increased in duration for about 3 ms, an effect caused by persistence of transmitter release. A similar change was obtained by replacing extracellular Ca 2+ by strontium, which inhibits the antiport. The antiport function, therefore, is to abbreviate the presynaptic Ca 2+ signal, making transmitter release briefer. This allows transmission to operate at high frequency. Following a brief period of stimulation, calcium transiently accumulates in synaptic vesicles where it is exchanged against transmitter. Calcium is subsequently cleared from the terminal, most probably by exocytosis.
Type of Medium:
Online Resource
ISSN:
0077-8923
,
1749-6632
DOI:
10.1111/nyas.2009.1152.issue-1
DOI:
10.1111/j.1749-6632.2008.04000.x
Language:
English
Publisher:
Wiley
Publication Date:
2009
detail.hit.zdb_id:
2834079-6
detail.hit.zdb_id:
211003-9
detail.hit.zdb_id:
2071584-5
SSG:
11
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