Abstract
We recorded miniature endplate currents (mEPCs) using simultaneous
voltage clamp and extracellular methods, allowing correction for
time course measurement errors. We obtained a 20-80\% rise time (tr)
of approximately 80 micros at 22 degrees C, shorter than any previously
reported values, and tr variability (SD) with an upper limit of
25-30 micros. Extracellular electrode pressure can increase tr and
its variability by 2- to 3-fold. Using Monte Carlo simulations, we
modeled passive acetylcholine diffusion through a vesicle fusion
pore expanding radially at 25 nm x ms(-1) (rapid, from endplate omega
figure appearance) or 0.275 nm x ms(-1) (slow, from mast cell exocytosis).
Simulated mEPCs obtained with rapid expansion reproduced tr and
the overall shape of our experimental mEPCs, and were similar to
simulated mEPCs obtained with instant acetylcholine release. We
conclude that passive transmitter diffusion, coupled with rapid expansion
of the fusion pore, is sufficient to explain the time course of experimentally
measured synaptic currents with trs of less than 100 micros.
- 8650164
- acetylcholine,
- animals,
- computer
- endplate,
- gov't,
- lizards,
- motor
- n,
- p.h.s.,
- research
- simulatio,
- support,
- synaptic
- u.s.
- vesicles,
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