title: Calcium-dependent synaptic vesicle trafficking underlies indefatigable release at the hair cell afferent fiber synapse.
abstract: Sensory hair cell ribbon synapses respond to graded stimulation in a linear, indefatigable manner, requiring that vesicle trafficking to synapses be rapid and nonrate-limiting. Real-time monitoring of vesicle fusion identified two release components. The first was saturable with both release rate and magnitude varying linearly with Ca(2+), however the magnitude was too small to account for sustained afferent firing rates. A second superlinear release component required recruitment, in a Ca(2+)-dependent manner, of vesicles not in the immediate vicinity of the synapse. The superlinear component had a constant rate with its onset varying with Ca(2+) load. High-speed Ca(2+) imaging revealed a nonlinear increase in internal Ca(2+) correlating with the superlinear capacitance change, implicating release of stored Ca(2+) in driving vesicle recruitment. These data, supported by a mass action model, suggest sustained release at hair cell afferent fiber synapse is dictated by Ca(2+)-dependent vesicle recruitment from a reserve pool.
authors.affiliation: Department of Otolaryngology, Stanford University School of Medicine, Stanford, CA 94304, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Schnee
authors.forename: Joseph
authors.initials: J
authors.lastname: Santos-Sacchi
authors.forename: Manuel
authors.initials: M
authors.lastname: Castellano-Muñoz
authors.forename: Jee-Hyun
authors.initials: JH
authors.lastname: Kong
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Ricci
mesh_terms: D000818:Animals; D001703:Biophysics; D002118:Calcium / Q000378:metabolism*; D025802:Electric Capacitance; D004558:Electric Stimulation; D005089:Exocytosis; D006198:Hair Cells, Auditory / Q000166:cytology*; D008954:Models, Biological; D017711:Nonlinear Dynamics; D018408:Patch-Clamp Techniques; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology*; D013572:Synaptic Vesicles / Q000502:physiology*; D014426:Turtles
chemical_list: D002118:Calcium