1. Active Zones and the Readily Releasable Pool of Synaptic Vesicles at the Neuromuscular Junction of the Mouse
- Author
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William J. Betz, Raquel Cano, Michael A. Gaffield, Rocío Ruiz, Lucia Tabares, Juan José Casañas, Universidad de Sevilla. Departamento de Bioquímica y Biología Molecular, and Universidad de Sevilla. Departamento de Fisiología Médica y Biofísica
- Subjects
Male ,Biophysics ,Neuromuscular Junction ,Presynaptic Terminals ,Motor nerve ,Nerve Tissue Proteins ,Stimulation ,In Vitro Techniques ,Biology ,Synaptic vesicle ,Biophysical Phenomena ,Exocytosis ,Neuromuscular junction ,Mice ,chemistry.chemical_compound ,medicine ,Animals ,Neurotransmitter ,Neurotransmitter Agents ,General Neuroscience ,Vesicle ,Miniature Postsynaptic Potentials ,Neuropeptides ,Articles ,Anatomy ,Electric Stimulation ,Cytoskeletal Proteins ,Electrophysiology ,medicine.anatomical_structure ,chemistry ,Female ,Synaptic Vesicles - Abstract
Synchronous neurotransmitter release is a highly regulated process that takes place at specializations at the presynaptic membrane called active zones (AZs). The relationships between AZs, quantal release, and vesicle replenishment are not well understood in a mature synapse. We have measured the number, distribution, and other properties of AZs in mouse motor nerve terminals and combined these observations with electrophysiological estimates of the size of the readily releasable pool (RRP) of synaptic vesicles. On average, we counted 850 AZs per terminal. Assuming two primary docked vesicles per AZ, we predict a total of ∼1700 vesicles optimally positioned for exocytosis. Electrophysiological estimates of the size of the RRP, using a simple kinetic model that assumes exponential depletion of the initial pool and refilling by recruitment, gave an average value of 1730 quanta during 100 Hz stimulation, in satisfying agreement with the morphology. At lower stimulus frequencies, however, the model revealed that the estimated RRP size is smaller, suggesting that not all AZs participate in release at low stimulation frequencies.
- Published
- 2011