title: The entry and clearance of Ca2+ at individual presynaptic active zones of hair cells from the bullfrog's sacculus.
abstract: Neurotransmitter is released when Ca2+ triggers the fusion of synaptic vesicles with the plasmalemma. To study factors that regulate Ca2+ concentration at the presynaptic active zones of hair cells, we used laser-scanning confocal microscopy with the fluorescent Ca2+ indicator fluo 3. The experimental results were compared with the predictions of a model of presynaptic Ca2+ concentration in which Ca2+ enters a cell through a point source, diffuses from the entry site, and binds to fixed or mobile Ca2+ buffers. The observed time course and magnitude of fluorescence changes under a variety of conditions were well fit when the model included mobile molecules as the only Ca2+ buffer. The results confirm the localized entry of Ca2+ underlying neurotransmitter release and suggest that Ca2+ is cleared from an active zone almost exclusively by mobile buffer.
authors.affiliation: Howard Hughes Medical Institute, Rockefeller University, New York, NY 10021-6399, USA.
authors.forename: N P
authors.initials: NP
authors.lastname: Issa
authors.forename: A J
authors.initials: AJ
authors.lastname: Hudspeth
mesh_terms: D000814:Aniline Compounds / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D005453:Fluorescence; D018069:Hair Cells, Vestibular / Q000378:metabolism*; D008564:Membrane Potentials; D017729:Presynaptic Terminals / Q000378:metabolism*; D011892:Rana catesbeiana; D012444:Saccule and Utricle / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors; D014966:Xanthenes / Q000378:metabolism
chemical_list: D000814:Aniline Compounds; D014966:Xanthenes; C059715:Fluo-3; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium