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  • Single-pixel optical fluctuation analysis of calcium channel function in active zones of motor nerve terminals.

Single-pixel optical fluctuation analysis of calcium channel function in active zones of motor nerve terminals.

The Journal of neuroscience : the official journal of the Society for Neuroscience (2011-08-05)
Fujun Luo, Markus Dittrich, Joel R Stiles, Stephen D Meriney
ABSTRACT

We used high-resolution fluorescence imaging and single-pixel optical fluctuation analysis to estimate the opening probability of individual voltage-gated calcium (Ca(2+)) channels during an action potential and the number of such Ca(2+) channels within active zones of frog neuromuscular junctions. Analysis revealed ∼36 Ca(2+) channels within each active zone, similar to the number of docked synaptic vesicles but far less than the total number of transmembrane particles reported based on freeze-fracture analysis (∼200-250). The probability that each channel opened during an action potential was only ∼0.2. These results suggest why each active zone averages only one quantal release event during every other action potential, despite a substantial number of docked vesicles. With sparse Ca(2+) channels and low opening probability, triggering of fusion for each vesicle is primarily controlled by Ca(2+) influx through individual Ca(2+) channels. In contrast, the entire synapse is highly reliable because it contains hundreds of active zones.

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3,4-Diaminopyridine, ≥98%