title: Single-pixel optical fluctuation analysis of calcium channel function in active zones of motor nerve terminals.
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.
authors.affiliation: Department of Neuroscience, Center for Neuroscience, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
authors.forename: Fujun
authors.initials: F
authors.lastname: Luo
authors.forename: Markus
authors.initials: M
authors.lastname: Dittrich
authors.forename: Joel R
authors.initials: JR
authors.lastname: Stiles
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Meriney
mesh_terms: D015761:4-Aminopyridine / Q000031:analogs & derivatives / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000077770:Amifampridine; D000818:Animals; D002038:Bungarotoxins / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism*; D003198:Computer Simulation; D004558:Electric Stimulation / Q000379:methods; D005614:Freeze Fracturing; D066298:In Vitro Techniques; D008959:Models, Neurological; D009010:Monte Carlo Method; D018482:Muscle, Skeletal / Q000294:innervation / Q000648:ultrastructure; D009469:Neuromuscular Junction / Q000166:cytology* / Q000187:drug effects; D055095:Optics and Photonics; D026902:Potassium Channel Blockers / Q000494:pharmacology; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism*; D011894:Rana pipiens; D011978:Receptors, Nicotinic / Q000378:metabolism; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism
chemical_list: D002038:Bungarotoxins; D015220:Calcium Channels; D026902:Potassium Channel Blockers; D011978:Receptors, Nicotinic; D015761:4-Aminopyridine; D000077770:Amifampridine; D002118:Calcium